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One of the most common ways to produce low-cost, quick-turnaround parts out of thermoplastics.
The term "3D printing" is most often used to refer to fused deposition modeling, or FDM. There are other less common / more expensive methods of 3D printing (stereolithography and selective laser sintering), but those will not be covered in this guide. Generally, all of these processes fall under the umbrella of "additive manufacturing". Here is a description of the FDM process from Wikipedia:
Filament is fed from a large coil through a moving, heated printer extruder head, and is deposited on the growing work. The print head is moved under computer control to define the printed shape. Usually the head moves in two dimensions to deposit one horizontal plane, or layer, at a time; the work or the print head is then moved vertically by a small amount to begin a new layer.
To illustrate the basics, here are some graphics:
While 3D printers can attempt most kinds of geometry, you will achieve far more success by considering the printability of your part during the design process. In addition, some parts are simply infeasible to print.
We recommend adding 0.010" - 0.020" or 0.3 - 0.5 mm of clearance between parts that you would like to fit together. Some printers extrude more than others, making this often an iterative process.
Printed parts are anisotropic, meaning they have different properties along different directions. This is a direct consequence of the fact that they are built up layer-by-layer.
Printers generally have different resolutions in different axes. Usually, the x-y resolution is far greater than the z-resolution; after all, the z-resolution is limited by the height of each layer.
Do not attempt to use a standard FEA simulation for anything more than a broad evaluation of a printed part. Printed parts almost always fail along layer lines (i.e. one layer separates from the next one up) and not within a layer. As a result, printed parts are often much weaker than expected in in the z (normal to layers) axis and with respect to bending moments in all directions.
This step is highly machine-dependent.
Most parts require some sort of post-processing.
Removal of supports is an exceedingly common task, but also a frequent source of injury. Here are some tips.
We recommend using your hands or needle-nosed pliers for the removal of supports. Do not use any sort of blade if at all possible. However, if you need to remove a brim or clean up a burr, we highly recommend the use of a deburring tool. These are fairly safe and extremely effective; use by gently pulling the tool toward yourself.
If you cannot find a deburring tool (STAR generally has one, as does Jacobs), you may use a knife as a last resort. We recommend using a 2-3 in-long folding or fixed-blade (where legal) knife with a locking blade. In the absence of a locking blade, a swiss army-style knife is acceptable. We strongly advise against using an X-Acto knife for this purpose, even though they are commonly found in maker spaces.
When using a knife to clean up a part, always CUT AWAY FROM YOURSELF AND OTHERS.
Use long, smooth strokes and do not attempt to force the blade. If the blade becomes stuck, just back out and try again with a more gentle angle/less pressure. Try to limit the use of a knife as a prybar; use pliers when possible. Again, CUT AWAY FROM YOURSELF AND OTHERS.
The advantage of printed parts is that it is usually possible to rapidly iterate on them to fix fit issues. That being said, it is often useful to remove a small amount of material to allow two parts to fit together. We recomend the use of files, not sandpaper whenever possible. Files will remove material far more quickly, at the cost of some flexibility.
While it may seem possible to sand down printed parts to achieve a smooth finish, this is almost always a colossal waste of everyone's time. Only do so if absolutely critical. Be warned that the plastic will likely appear to whiten a bit as the sanding abrades the surface.
You may use a thin, clear epoxy to coat parts for protection and aesthetics. We recommend using a disposable foam brush and an epoxy with a long enough working time that it does not get sticky while being applied. This method may also work together with sanding (see above).
If you have an ABS part, it is possible to smooth the surface using acetone vapors. Here is a link to a reasonable tutorial. Do NOT follow a tutorial making use of a hot plate, stove, etc; this is unnecessary and dangerous, risking a safety incident to save an hour or two. Without heat, this is generally a safe process. Be warned that the acetone vapors may compromise the structural integrity of your part over time; watch for cracks and increased brittleness. There are no reasonably safe solvents that can smooth PLA parts; the only such chemicals are designed to attack organic matter and are thus highly toxic to humans. Do not attempt to acquire them.
Most people use it to mill PCBs but that's boring
The Othermill creates very dimensionally accurate parts, but may be slower and more complex than other prototyping processes. If your part significantly depends on being diemnsionally accurate (for example, low backlash gears), then the othermill may be a good choice. Laser cutters produce a noticeable and uneven kerf, and 3D printing (FDM) cannot produce very fine details well.
The smallest commonly available Othermill bit that can be used to mill out parts is the 1/32" bit. This bit can cut up to materials that are 0.125" thick. Be aware that machining speed can be significantly slowed down the smaller the bit size is. Refer to online resources on Computer-Aided Machining (CAM) best practices on what bit to choose.
In order of machinability, here are the materials the authors have used successfully on the Othermill:
Delrin (acetyl homopolymer resin)
Lexan (polycarbonate)
Aluminum
The Othermill should not be used to cut steel.
Download the Jacobs Hall tool library from the Jacobs Hall bcourses training for the Othermill. Do not download the tool library directly from Bantam Tools, as it contains some inaccuracies.
Measure the stock and CAD the part to be no greater than the thickness of the stock. If the part is mostly flat, have its thickness match the thickness of the stock unless facing is needed.
Set up the Work Coordinate System as follows. Other tutorials may recommend you set the origin at the top of the stock, but this can cause poor results and collisions with the spoilboard. While these toolpaths will be offset in the Z direction when we import them into the Bantam Tools software, we will correct this at a later time.
Input the accurate dimensions of your stock in the Stock tab. Then, adjust the position of your part relative to the edges of the stock. Items in red boxes should generally be changed for each part or stock piece, while the rest should match the image.
The term "feeds and speeds" refers to how quickly the tool rotates and how quickly it moves along the x, y, and z axis. Smaller tools should generally be used with slower feeds and speeds.
Aluminum is significantly tougher than plastics. most important is the stepdown on operations with multiple depths; use a stepdown of at most 0.004". For drilling, use a very conservative chip clearing toolpath, pecking in 0.001" increments at a speed of 0.5 in/min. Milling aluminum with the Othermill is somewhat of an acquired skill, so don't worry if you break a bit or two at first. Do not attempt to mill aluminum with anything smaller than a 1/16" endmill.
Climb milling will result in a better finish and longer tool life.
Check the "keep tool down" checkbox or cuts with multiple depths will lift the tool each time.
Always keep the Ramp checkbox checked and generally use a ramp angle of 3-5 degrees depending on the material (larger angle ok on softer materials).
Facing
Bore
2D Contour
Always simulate your toolpaths in Fusion before exporting them for use on the machine. This is the primary way to prevent damage to the machine, the tooling, and the part
Open the simulation settings and check the "Stock" box. You can change from the default green color by changing the material options, but this is not important. Watch the entire simulation; if it is long, speed it up as little as necessary to ensure you catch any unintended behavior.
Right click on each operation on the left dropdown and select "Post Process". Select the settings for the Othermill and give your toolpath a descriptive name and number: e.g. 1_facing, 2_bore, etc. Numbering will help you keep track of the order in which to run each operation.
This step will produce .gcode files; these are text files containing a list of instructions that will be fed to the Othermill during operation. Make sure you save the gcode files in an accessible location on your filesystem.
Turn on the Othermill using the power switch at the back left corner.
Ensure that the emergency stop (big red button) is not engaged.
Connect the machine to a computer that has Bantam Tools installed.
Open Bantam Tools, and home the machine.
If using the fixturing bracket, locate the bracket by pressing "locate".
Insert a 1/8" endmill upside down (with the cutting flute inside the collet).
Load the material (tbd)
Load the toolpaths. Click the "Open Files" button and select your .gcode files.
Offset the toolpaths. If you do not perform this step, nothing will be milled. For each toolpath, open the "Placement" dropdown and enter -[stock thickness] under the z-offset. For exampele, if I have a sheet of nominally 1/8" Delrin that I have measured to be 0.135" thick, I would put "-0.130 in". You may also add x and y offsets, but be sure to repeat the process for each individual operation / toolpath.
Load a tool by clicking "Change...". Mount the desired bit and select it from the drop down menu. Click "Locate" and ensure that the mill has moved the bit above a clear section of the spoilboard (metal bed). If not, manually adjust. Confirm the position, and the machine will begin to move the bit down to touch the bed. While this is happening, make sure you are ready to stop the machine (press "ESC" or the emergency stop to stop). Once the bit has made contact with the bed, the machine should immediately stop trying to move the bit down. If you head any sound of resistance STOP THE MILL and try again.
The FabLight is a laser cutter designed to safely cut both metal sheets and tubes.
For more information about the process of using the FabLight (e.g., preparing and loading a file/CAD drawing) and a full list of approved materials, please visit the Jacobs bCourses page. In a non-COVID year, both the online quiz and in-person training is required prior to being able to use the FabLight.
The FabLight is more precise than a water jet and has a less steep learning curve. In a non-COVID year, it is also more available due to being located in the general all-purpose makerspaces (studios 110 and 120) and not the metal shop with its more limited hours. For Jacobs Project Support during COVID, the FabLight similarly has a faster turnaround time and can produce parts more quickly once a request is received.
The disadvantage is that the FabLight of course cannot cut through as thick materials as a water jet. The maximum thickness that a STAR member has previously cut through on the FabLight without issue is 1/8" stainless steel.
November 2020: The Payload subteam successfully laser cut leaf springs for the Bear Force One payload structure out of 1/32" 6061 aluminum, available through the Jacobs Material store.
What good is MSE anyway?
Delrin is a low-friction plastic that is extremely machineable; Delrin parts can be made on a laser cutter or mill. For small, precise parts, the Othermill is a great way to machine Delrin. Delrin is fairly strong, although it will deform substantially under higher loads.
Acrylic (in the form that Jacobs Hall sells) is a fairly brittle material that we recommend avoiding for use in flight parts. Acrylic is occaisionally useful for enclosures or signs. Polycarbonate is recommended as a substitute for acrylic unless the material must be laser cut.
ABS is a common 3D-printing plastic. It is slightly more ductile than PLA, the other common printing plastic, but otherwise similar. While there is a common perception that ABS is "stronger" than PLA, this is somewhat inaccurate; for most uses, they are indistinguishable.
ABS
PLA
ABS printers at Jacobs have soluble supports
Usually not available with soluble supports at Jacobs
Much higher tendency to warp, especially without enclosed, heated build envelope
Doesn't warp nearly as much
ABS printers at Jacobs are much higher resolution than the Type A / Ultimaker
Type A prints are typically the worst quality achievable, Ultimakers are slightly better
Parts may bend instead of breaking, higher elongation at break
May crack if dropped, rather than bending, but higher tensile strength
Dimensions and Fortus are limited and often in use, may require joining a lengthy queue
Type A and Ultimakers are more plentiful and more frequently free, with low turnaround time
Free at Jacobs
Fumes may give you cancer, kills the planet
Food-safe, biodegradable (with 6 months in a specialized composting facility, don't worry)
Gets softer at slightly lower temperatures
Requires Jacobs hands-on training
On-line training only needed
Little ABS personally owned by team members
In-stock at homes of team members for printing
6061 aluminum is a fairly machinable material that can be processed with a waterjet cutter, bandsaw, fiber laser cutter, mill, lathe, and/or welding machine. Compared to most plastics and wood, aluminum is very strong; consider using aluminum for parts where strength is more important than weight. Aluminum is fairly soft, so do not design parts that require threads to be cut into aluminum; instead, use threaded inserts. We generally use the 6061 alloy, but others are acceptable; check with an expert before making the decision to use another alloy.
This is the material we are currently using for our thrust chamber. Otherwise, generally avoid brass as there are better and cheaper substitutes available (usually aluminum).
Jacobs Hall sells plywood in several sizes and thicknesses for laser cutting. Common thicknesses are 0.25 in and 0.125 in. It is important to note that wood is anisotropic; its material properties vary significantly according to the direction of the forces applied. Wood can be used for structural parts, but it may be better to consider Lexan and aluminum first. Jacobs plywood is often used to make non-structural jigs, holders, etc.
Lexan is extremely strong, although it will flex slightly under load. Most of our Lexan parts are produced with a waterjet cutter, although they can be milled, bored, etc. afterward if needed. We are unable to cut Lexan with lasers; if laser cutting is desired and strength is not a priority, consider using Delrin instead.
PLA is a bio-based plastic commonly used for 3D printing. It is slightly more brittle than ABS, but it can absorb more energy before failure. See the "Acrylonitrile Butadiene Styrene (ABS)" entry for a comparison of PLA with ABS. It is also more readily available than any other 3D printing materials in the Jacobs Hall Makerspace. PLA is a good candidate for parts with complex geometry that are non-structural in nature. It is important to note that printed parts, like wood, are anisotropic; they fail much more easily in some directions (along layer lines) than others.
ESRA guidelines say we pretty much can't use stainless steel for anything important. That being said, other projects or non-critical parts might be allowed to use stainless steel; check the regulations! Many low-strength fasteners are made out of 18-8 stainless.
This manufacturing guide takes you step-by-step from a SolidWorks model to a laser cut part.
Laser cutting is a fast manufacturing and prototyping method suitable for highly planar parts.
Start by opening the SolidWorks part you want to laser cut.
Select the surface that you want the laser cutter to follow by clicking on the surface, as shown in the image below.
In the top menu, go to "File">"Save As"
From the file type drop down box, you must select a DXF (.dxf) file
Click "Yes", and a properties box will appear on the left sidebar. The selected face should be automatically filled in the "Entities to Export" box. Click the check mark and then "Save" to proceed.
We are now done with SolidWorks, but before exiting the program please take note of the dimension units of the part. In the part above, it is in inches (IPS)
Now open Adobe Illustrator, click on "File">"Open" and select your .dxf file.
A very important window will pop up. Under "Artwork Scale" you must select "Scale By: 100%" the "Scale" box must be 1.
Now, remembering what your part dimension units were, you must select the correct units you used in SolidWorks in the "Unit(s)" box. For IPS, select "Inches" from the drop down and for MMGS select "Millimeters".
After selecting the unit, the value of the "Unit(s)" box may change. This value must be set to 1.
Have you ensured that your DXF scale options are correct? It is difficult to guess whether your part has been correctly scaled or not after these options have been set.
You are now ready to proceed with processing the illustrator file.
Delete any text that SolidWorks may have generated (ie. "SolidWorks Educational Product. For instructional use only)
Select all of the lines and set the stroke width to 0.001in and color to pure red. (These steps are detailed further on in this guide)
You have now successfully prepared a SolidWorks part to be laser cut. Follow the rest of this guide for further instructions.
Flip the lever on the wall next to the laser cutter before operation (You should hear air start blowing)
Make sure there is not something hidden in the background that doesn't immediately show up on illustrator
Ensure that everything in illustrator is a vector
Lift the hood and check where the laser is pointing to confirm where exactly you are cutting
Check the extremes of the shape being cut on the material you are cutting
Try to avoid using warped materials
Jacobs Hall;
Three Universal VLS 6.60 (left) Located in 110c. and one Universal ILS 12.75 (right) Located in 120.
Invention Lab;
One VLS2.30 Located at the Citris Invention Lab.
Cory Student Workshop;
One PLS4.75 Located at the CSW.
In this course you will learn how to use the Universal Laser cutters to cut, score, and/or engrave a variety of materials. Laser cutting works by directing a high-power laser through optics onto a material which either cuts through or etches, depending on settings used. It is useful for precisely cutting 2D geometries and engraving images onto materials. Completion of this class will allow you to sign up for the Hands-On check out at Jacobs Hall. Once that step is completed, you will have access to the Universal lasers in Jacobs Hall, the Invention Lab, and the Cory Student Workshop.
Laser cutters are only operable while Design Specialists, or Student Supervisors with training are present.
Remember the buddy system- there must be a second person within earshot of you while working on the laser. Buddy system requirement will be a superuser requirement for CSW.
Any operation of the laser system is a potential fire hazard.
Most, if not all, materials are combustible in certain circumstances. Acrylic is especially flammable when vector cutting. Wood, paper, and plastics can all combust. NEVER OPERATE THE LASER SYSTEM WITHOUT CONSTANT SUPERVISION OF THE CUTTING AND ENGRAVING PROCESS. Exposure to the laser beam may cause ignition of combustible materials which can lead to a fire.
Any fire lasting more than half a second must be controlled. This list of steps begins with the simplest and escalates. Follow as many steps as necessary to extinguish any fire:
Lift the top door. This often stops small flames.
Turn off the exhaust system.
Blow on the material.
Remove the material if it is safe to grab a corner.
Spray water with spray bottle. Blue spray bottles are kept near each laser system.
If the fire is unmanageable, use the nearest fire alarm to contact the local fire department and evacuate the building.
Notify a technician immediately, even if a fire is small and easily extinguished. It’s important to know why it occurred, assess any damage, and prevent it from repeating. Discontinue using the laser until a technician has assessed that it is okay to resume.
Circumstances that can cause fire:
Files with lots of dense geometry very close together. This can cause the laser to repeatedly cut the same area, build up heat in one area and ignite it
Similarly, power settings too high for the material being cut and/or speed settings too slow
The laser is not focused properly (focus carriage is too close or too far from material). The laser is usually set up to focus automatically based on the thickness entered by the user but it can be disabled manually. Ask a Design Specialist to assist with this.
Attempting to cut materials on top of each other
Always remove all material including scrap material from the machine after use. Cordless vacuums are kept near the laser system. It is required to remove the cutting table and vacuum out the interior. Scrap material left in the laser system including materials that collect in the removable cutting table can be a fire hazard.
Exposure to the laser beam may cause physical burns and can cause severe eye damage. Proper use and care of this system are essential to safe operation.
Properly using the installed fume exhaust system is mandatory when operating the laser system. Fumes and smoke from the engraving process must be extracted from the laser system and filtered or exhausted outside.
Some materials, when engraved or cut with a laser, can produce toxic and corrosive fumes. If you are not sure of a material is laser-safe, you can consult with shop staff. We recommend that you obtain the material’s Safety Data Sheet (SDS) from the manufacturer of every material you intend to process in the laser system. The SDS discloses all of the hazards when handling or processing a particular material. Do not process any material that causes chemical deterioration of the laser system such as rust, metal etching or pitting, peeling paint, etc.
The Invention Lab lasers are on a first-come basis. Please be kind to your fellow users and be accommodating if you have a very long job.
For the Jacobs Hall lasers, the reservation system can be found at http://reserve.jacobshall.org/ (Links to an external site.)Links to an external site.. Please prepare your cut file in advance and estimate the cutting time using the Universal Laser software. See the Laser Cutter Interface section below regarding estimating cutting time.
Reservations can be made up to 7 days in advance.
Late & no-shows: After 10 minutes a reservation is forfeited and the remainder of the time is given to the first drop-in user. If you cannot make it to an appointment, please cancel it before it begins.
Unreserved times are designated drop-in use by anyone until the next reservation.
For the CSW, access requires the presence of superuser on first come first serve basis by checking shop calendar for superuser availability. Limiting access for maker-pass users for fairness to non-maker-pass users.
If a laser system breaks or is damaged while you are using it, inform the shop staff. Equipment damage is a normal part of the shop environment; for safety reasons it is important to inform a shop staff member immediately.
Always clean up fully after yourself. No material scraps should remain in the shop or in the machines.
If a laser system is not cutting material, the lens may need to be cleaned. Do not increase the intensity as this can cause the lens to burst. Notify a shop staff member and the lens can be cleaned if needed.
For your health safety and others in the shop, processing any material that is not laser-safe is against shop policy. Always check with a technician before assuming any material NOT purchased at the Jacobs Online store is okay.
PVC (aka Polyvinyl chloride, vinyl, pleather) is not laser safe. Chlorinated materials ( are corrosive to the machine and toxic
Chlorinated rubbers also release chlorine. Some paints contain chlorinated rubber.
Nitrile rubber releases hydrogen cyanide when combusted
Polystyrene foam (aka Styrofoam) - Melts and catches fire. Very dangerous.
Almost any foam - Including Foam core, polypropylene foam, etc. Very dangerous.
Construction grade plywood - Most plywood sold in hardware stores is not bonded with modified adhesives making it prone to smoking, flaming, charring at the edges and producing toxic fumes (Best Plywood for Laser Cutting (Links to an external site.)Links to an external site.: No Knots, Thicker/Less Ply, Interior Grade, urea-formaldehyde(UF) or melamine-formaldehyde(off-gasses less formaldehyde) glue (Links to an external site.)Links to an external site.)
ABS off-gases hydrogen cyanide in fumes, a chemical known to be very toxic and has been used as a chemical warfare agent.
Polycarbonate (aka Lexan) - absorbs infrared radiation, causing it to melt and warp. Looks very similar to acrylic sheets.
Remember that all materials create fumes when laser cut. "Safe" materials are judged as such by not being overly combustible or releasing corrosive, mutagenic, or poisonous gases when laser cut.Always check with a technician before assuming any material NOT purchased at the Jacobs Online store is okay.
Paper / Cardstock - can be both etched and cut
Wood - can be both etched and cut
Cast Acrylic can be cut or rastered (has a frosted, translucent appearance)
Extruded Acrylic - can be cut (does not frost when etched)
Delrin - hard plastic, good for mechanical parts like gears (available in different hardnesses)
Cotton / Felt / Hemp - cuts well, engraves well
Polyester fabric - cuts okay, edges melt a bit, doesn’t engrave well
Leather - natural leather only, not synthetic “pleather”
Anodized Aluminum - can be etched (Black anodized aluminum provides best contrast out of all anodized aluminum)
Ceramic / Stone - Engraving is possible on porcelain, ceramic, terracotta slate, marble and stone
Brass - Uncoated brass can not be etched with a laser, it needs to have some kind of coating (such as paint).
Glass - Can be etched only. Must be flat. Etching colored glass has best visual results.
Rubber - Buna-N Rubber, Polyurethane rubber, natural rubber (no nitrile rubber or any chlorine-containing rubber)
Step 0 - File Setup
Files can be set up ahead of time to use time efficiently. Universal laser systems operate in one of two modes. A raster mode, in which images are marked or engraved into a material by etching a pattern of dots into the material at high resolutions up to 1000 dpi, and a vector mode in which the laser follows a two dimensional path to cut or mark a shape into a material. The printer driver determines whether an element in the graphic data being printed is a vector or raster object by its width.
The 3 laser cutters in 110C can cut 32" wide by 18" high, and the laser cutter in 120 can cut 48" wide by 24" high. The CSW laser cutter bed size is 18"x24". If you want to cut using the full cut area, set up the file you want to cut using 24", 32" or 48" for the width, and 18" or 24" for the height. Also select color mode RGB. This is crucial because the laser cutter software will not understand other modes.
Line thickness
Only lines and curves with a thickness of .001 in (.072 pt) or less will be interpreted as vector objects. All other elements of the graphic, including JPEG images, being printed will be interpreted as raster objects. In order to print vector elements, the software you are printing from must support creation of lines with a thickness of .001 in (.072 pt) or less. This includes Adobe Illustrator, Rhino, SolidWorks, AutoCAD, and other drafting software.
Line Color
Red lines indicate a line to be cut, Blue lines indicate a line to be scored, Black lines indicate a line to be engraved. When changing colors in Illustrator, use the following instructions to make sure you are using true RGB values;
1. To change line color, make sure your image is selected, then click on the color pallet icon in the tool bar;
2. Click on the "more" dropdown icon in the upper right of the colors box to choose "Show Options". Make sure RGB is also selected;
3. To make a cut or score line Make sure that the color choice is for "stroke" by clicking on the stroke square (which looks like a hollow red rectangle in the below icon). Now enter the correct values for the type of operation you want. For instance, To make a cut line enter 255 in the R setting, 0 in the G setting, and 0 in the B setting. To make a score line enter 0 in the R setting, 0 in the green setting, and 255 in the blue setting.
Step 1 - Clean off honeycomb cutting bed. Debris can be a fire hazard.
Step 2 - Load and Position Material
*When in the Invention Lab, open the ventilation gate located on the wall behind and to the right of the machine
Open the top door to the laser system and place material to be laser processed onto the engraving table. You may need to manually move the support table down to allow clearance to fit thicker materials into the machine. The material must be flat and consistent in thickness. The machine cannot remain focused on warped materials or materials that change in thickness/height.
*When at the CSW, turn the machine on in the correct order;
1.Press the power button on BOFA fume extractor
2. Turn the air compressor 90 degrees counterclockwise
3. Turn on the Laser Cutter
Step 3 - Sending to Universal Control Panel
Have you ensured that your illustrator file is the correct scale? If you do not know the scale, press Ctrl-R to bring up the rulers. See if your part is reasonably sized.
While still in Illustrator, click Print to open the printing options.
Click "set up" in the bottom, right corner
Open the preferences dialog. This will load the laser cutter's material settings database.
Laser Cutter Interface
Vector cutting depth and raster engraving depth (or marking intensity if you are surface marking only) are controlled by specifying the speed of processing and the laser power level for raster engraving and by specifying the speed of processing, laser power level and number of pulses per inch (PPI) for vector cutting and marking.
Materials are listed under various categories. Under the appropriate category or sub-category, select the material you are processing.
Enter the material thickness. Use calipers to measure the thickness accurately.
Click Defaults to reset the Intensity Adjustment sliders to 0%. Only adjust vector cutting intensity if needed.
Click OK, then click Print.
At the bottom right of the screen, click the Universal Control Panel icon.
Basic View (default mode)
• The Basic View shows a preview window of the job currently selected.
• The cursor becomes a magnifying glass (Zoom Tool) if you pass it over the preview window. Left-clicking the mouse zooms in and right-clicking zooms out. (Mouse scroll wheel can be used in any mode to zoom in and out.)
• Selecting the Settings button takes you back to the printer driver interface to allow you to change most of the settings for the job selected. Keep in mind that some settings cannot be changed after printing from your graphics program, such as print density and vector quality. If a setting is not adjustable after printing from your graphics program, it will be grayed out or not appear at all when you press the settings button in the UCP.
The Focus View feature allows you to quickly manually move the focus carriage to a desired position in the material processing field. This is useful for focusing, as well as testing whether the geometry falls within the material.
The Relocate feature gives you the ability to move the image in the selected job to another area of the engraving field. This feature does not permanently modify the original image location.
The Duplicate feature gives you the ability duplicate an image in a grid pattern. You can select how many rows and columns of the image as well as the spacing between the rows and columns.
The estimate feature approximately calculates the amount of time it will take the laser system to process the selected job. For more complex jobs, the estimate feature can take a while to estimate the job completion time. A job can be estimated while a machine is disconnected or turned off.
Make sure the material is positioned correctly within the engraving area, and the geometry is positioned correctly in the Control Panel.
Close the top door.
Check that the fume exhaust is running and compressed air is flowing. Controls for each of these should be labeled near the laser.
Always ask a Design Specialist if you have any issues setting up your cut file or preparing the laser cutter.
Press the green START button on the UCP to begin laser processing.
The Universal software should be set to automatically focus based on the material thickness specified.
Order of execution when using the materials database tab proceeds with raster objects first, then vector marking objects and finally vector cutting objects.
It is not guaranteed that the laser will successfully cut through a material. It’s recommended to do a quick test cut:
Create a very small shape (such as a ½" - ¾” diameter circle) and position it in a marginal part of your material or another piece of the same material.
Cut the test geometry. As always, watch for anything
On the UCP, click “Settings” to re-open cut settings.
Adjust the intensity sliders on the top right but increase by small increments.
Then move the test cut shape in order to repeat.
Universal Laser Systems Safety and Operation Reference
Jacobs Hall;
Three Universal VLS 6.60 (left) Located in 110c. and one Universal ILS 12.75 (right) Located in 120.
Invention Lab;
One VLS2.30 Located at the Citris Invention Lab.
Cory Student Workshop;
One PLS4.75 Located at the CSW.
Course Synopsis
In this course you will learn how to use the Universal Laser cutters to cut, score, and/or engrave a variety of materials. Laser cutting works by directing a high-power laser through optics onto a material which either cuts through or etches, depending on settings used. It is useful for precisely cutting 2D geometries and engraving images onto materials. Completion of this class will allow you to sign up for the Hands-On check out at Jacobs Hall. Once that step is completed, you will have access to the Universal lasers in Jacobs Hall, the Invention Lab, and the Cory Student Workshop.
Laser Safety and Procedures
Laser cutters are only operable while Design Specialists, or Student Supervisors with training are present.
Remember the buddy system- there must be a second person within earshot of you while working on the laser. Buddy system requirement will be a superuser requirement for CSW.
Any operation of the laser system is a potential fire hazard.
Most, if not all, materials are combustible in certain circumstances. Acrylic is especially flammable when vector cutting. Wood, paper, and plastics can all combust. NEVER OPERATE THE LASER SYSTEM WITHOUT CONSTANT SUPERVISION OF THE CUTTING AND ENGRAVING PROCESS. Exposure to the laser beam may cause ignition of combustible materials which can lead to a fire.
Fire Protocol
Any fire lasting more than half a second must be controlled. This list of steps begins with the simplest and escalates. Follow as many steps as necessary to extinguish any fire:
Lift the top door. This often stops small flames.
Turn off the exhaust system.
Blow on the material.
Remove the material if it is safe to grab a corner.
Spray water with spray bottle. Blue spray bottles are kept near each laser system.
If the fire is unmanageable, use the nearest fire alarm to contact the local fire department and evacuate the building.
Notify a technician immediately, even if a fire is small and easily extinguished. It’s important to know why it occurred, assess any damage, and prevent it from repeating. Discontinue using the laser until a technician has assessed that it is okay to resume.
Circumstances that can cause fire:
Files with lots of dense geometry very close together. This can cause the laser to repeatedly cut the same area, build up heat in one area and ignite it
Similarly, power settings too high for the material being cut and/or speed settings too slow
The laser is not focused properly (focus carriage is too close or too far from material). The laser is usually set up to focus automatically based on the thickness entered by the user but it can be disabled manually. Ask a Design Specialist to assist with this.
Attempting to cut materials on top of each other
Always remove all material including scrap material from the machine after use. Cordless vacuums are kept near the laser system. It is required to remove the cutting table and vacuum out the interior. Scrap material left in the laser system including materials that collect in the removable cutting table can be a fire hazard.
Exposure to the laser beam may cause physical burns and can cause severe eye damage. Proper use and care of this system are essential to safe operation.
Properly using the installed fume exhaust system is mandatory when operating the laser system. Fumes and smoke from the engraving process must be extracted from the laser system and filtered or exhausted outside.
Some materials, when engraved or cut with a laser, can produce toxic and corrosive fumes. If you are not sure of a material is laser-safe, you can consult with shop staff. We recommend that you obtain the material’s Safety Data Sheet (SDS) from the manufacturer of every material you intend to process in the laser system. The SDS discloses all of the hazards when handling or processing a particular material. Do not process any material that causes chemical deterioration of the laser system such as rust, metal etching or pitting, peeling paint, etc.
Appointment Reservation System
The Invention Lab lasers are on a first-come basis. Please be kind to your fellow users and be accommodating if you have a very long job.
For the Jacobs Hall lasers, the reservation system can be found at http://reserve.jacobshall.org/ (Links to an external site.)Links to an external site.. Please prepare your cut file in advance and estimate the cutting time using the Universal Laser software. See the Laser Cutter Interface section below regarding estimating cutting time.
Reservations can be made up to 7 days in advance.
Late & no-shows: After 10 minutes a reservation is forfeited and the remainder of the time is given to the first drop-in user. If you cannot make it to an appointment, please cancel it before it begins.
Unreserved times are designated drop-in use by anyone until the next reservation.
For the CSW, access requires the presence of superuser on first come first serve basis by checking shop calendar for superuser availability. Limiting access for maker-pass users for fairness to non-maker-pass users.
Laser Work Space Etiquette
If a laser system breaks or is damaged while you are using it, inform the shop staff. Equipment damage is a normal part of the shop environment; for safety reasons it is important to inform a shop staff member immediately.
Always clean up fully after yourself. No material scraps should remain in the shop or in the machines.
If a laser system is not cutting material, the lens may need to be cleaned. Do not increase the intensity as this can cause the lens to burst. Notify a shop staff member and the lens can be cleaned if needed.
BANNED Materials
For your health safety and others in the shop, processing any material that is not laser-safe is against shop policy. Always check with a technician before assuming any material NOT purchased at the Jacobs Online store is okay.
PVC (aka Polyvinyl chloride, vinyl, pleather) is not laser safe. Chlorinated materials ( are corrosive to the machine and toxic
Chlorinated rubbers also release chlorine. Some paints contain chlorinated rubber.
Nitrile rubber releases hydrogen cyanide when combusted
Polystyrene foam (aka Styrofoam) - Melts and catches fire. Very dangerous.
Almost any foam - Including Foam core, polypropylene foam, etc. Very dangerous.
Construction grade plywood - Most plywood sold in hardware stores is not bonded with modified adhesives making it prone to smoking, flaming, charring at the edges and producing toxic fumes (Best Plywood for Laser Cutting (Links to an external site.)Links to an external site.: No Knots, Thicker/Less Ply, Interior Grade, urea-formaldehyde(UF) or melamine-formaldehyde(off-gasses less formaldehyde) glue (Links to an external site.)Links to an external site.)
ABS off-gases hydrogen cyanide in fumes, a chemical known to be very toxic and has been used as a chemical warfare agent.
Polycarbonate (aka Lexan) - absorbs infrared radiation, causing it to melt and warp. Looks very similar to acrylic sheets.
Laser safe materials
Remember that all materials create fumes when laser cut. "Safe" materials are judged as such by not being overly combustible or releasing corrosive, mutagenic, or poisonous gases when laser cut.Always check with a technician before assuming any material NOT purchased at the Jacobs Online store is okay.
Paper / Cardstock - can be both etched and cut
Wood - can be both etched and cut
Cast Acrylic can be cut or rastered (has a frosted, translucent appearance)
Extruded Acrylic - can be cut (does not frost when etched)
Delrin - hard plastic, good for mechanical parts like gears (available in different hardnesses)
Cotton / Felt / Hemp - cuts well, engraves well
Polyester fabric - cuts okay, edges melt a bit, doesn’t engrave well
Leather - natural leather only, not synthetic “pleather”
Anodized Aluminum - can be etched (Black anodized aluminum provides best contrast out of all anodized aluminum)
Ceramic / Stone - Engraving is possible on porcelain, ceramic, terracotta slate, marble and stone
Brass - Uncoated brass can not be etched with a laser, it needs to have some kind of coating (such as paint).
Glass - Can be etched only. Must be flat. Etching colored glass has best visual results.
Rubber - Buna-N Rubber, Polyurethane rubber, natural rubber (no nitrile rubber or any chlorine-containing rubber)
Step 0 - File Setup
Files can be set up ahead of time to use time efficiently. Universal laser systems operate in one of two modes. A raster mode, in which images are marked or engraved into a material by etching a pattern of dots into the material at high resolutions up to 1000 dpi, and a vector mode in which the laser follows a two dimensional path to cut or mark a shape into a material. The printer driver determines whether an element in the graphic data being printed is a vector or raster object by its width.
The 3 laser cutters in 110C can cut 32" wide by 18" high, and the laser cutter in 120 can cut 48" wide by 24" high. The CSW laser cutter bed size is 18"x24". If you want to cut using the full cut area, set up the file you want to cut using 24", 32" or 48" for the width, and 18" or 24" for the height. Also select color mode RGB. This is crucial because the laser cutter software will not understand other modes.
File Requirements
Line thickness
Only lines and curves with a thickness of .001 in (.072 pt) or less will be interpreted as vector objects. All other elements of the graphic, including JPEG images, being printed will be interpreted as raster objects. In order to print vector elements, the software you are printing from must support creation of lines with a thickness of .001 in (.072 pt) or less. This includes Adobe Illustrator, Rhino, SolidWorks, AutoCAD, and other drafting software.
Line Color
Red lines indicate a line to be cut, Blue lines indicate a line to be scored, Black lines indicate a line to be engraved. When changing colors in Illustrator, use the following instructions to make sure you are using true RGB values;
1. To change line color, make sure your image is selected, then click on the color pallet icon in the tool bar;
2. Click on the "more" dropdown icon in the upper right of the colors box to choose "Show Options". Make sure RGB is also selected;
3. To make a cut or score line Make sure that the color choice is for "stroke" by clicking on the stroke square (which looks like a hollow red rectangle in the below icon). Now enter the correct values for the type of operation you want. For instance, To make a cut line enter 255 in the R setting, 0 in the G setting, and 0 in the B setting. To make a score line enter 0 in the R setting, 0 in the green setting, and 255 in the blue setting.
Laser System
Step 1 - Clean off honeycomb cutting bed. Debris can be a fire hazard.
Step 2 - Load and Position Material
*When in the Invention Lab, open the ventilation gate located on the wall behind and to the right of the machine
Open the top door to the laser system and place material to be laser processed onto the engraving table. You may need to manually move the support table down to allow clearance to fit thicker materials into the machine. The material must be flat and consistent in thickness. The machine cannot remain focused on warped materials or materials that change in thickness/height.
*When at the CSW, turn the machine on inthe correct order;
1.Press the power button on BOFA fume extractor
2. Turn the air compressor 90 degrees counterclockwise
3. Turn on the Laser Cutter
Step 3 - Sending to Universal Control Panel
While still in Illustrator, click Print to open the printing options.
Click "set up" in the bottom, right corner
Open the preferences dialog. This will load the laser cutter's material settings database.
Laser Cutter Interface
Vector cutting depth and raster engraving depth (or marking intensity if you are surface marking only) are controlled by specifying the speed of processing and the laser power level for raster engraving and by specifying the speed of processing, laser power level and number of pulses per inch (PPI) for vector cutting and marking.
Materials are listed under various categories. Under the appropriate category or sub-category, select the material you are processing.
Enter the material thickness. Use calipers to measure the thickness accurately.
Click Defaults to reset the Intensity Adjustment sliders to 0%. Only adjust vector cutting intensity if needed.
Click OK, then click Print.
At the bottom right of the screen, click the Universal Control Panel icon.
Basic View (default mode)
• The Basic View shows a preview window of the job currently selected.
• The cursor becomes a magnifying glass (Zoom Tool) if you pass it over the preview window. Left-clicking the mouse zooms in and right-clicking zooms out. (Mouse scroll wheel can be used in any mode to zoom in and out.)
• Selecting the Settings button takes you back to the printer driver interface to allow you to change most of the settings for the job selected. Keep in mind that some settings cannot be changed after printing from your graphics program, such as print density and vector quality. If a setting is not adjustable after printing from your graphics program, it will be grayed out or not appear at all when you press the settings button in the UCP.
The Focus View feature allows you to quickly manually move the focus carriage to a desired position in the material processing field. This is useful for focusing, as well as testing whether the geometry falls within the material.
The Relocate feature gives you the ability to move the image in the selected job to another area of the engraving field. This feature does not permanently modify the original image location.
The Duplicate feature gives you the ability duplicate an image in a grid pattern. You can select how many rows and columns of the image as well as the spacing between the rows and columns.
The estimate feature approximately calculates the amount of time it will take the laser system to process the selected job. For more complex jobs, the estimate feature can take a while to estimate the job completion time. A job can be estimated while a machine is disconnected or turned off.
Before Starting The Laser Cutter
Make sure the material is positioned correctly within the engraving area, and the geometry is positioned correctly in the Control Panel.
Close the top door.
Check that the fume exhaust is running and compressed air is flowing. Controls for each of these should be labeled near the laser.
Always ask a Design Specialist if you have any issues setting up your cut file or preparing the laser cutter.
Press the green START button on the UCP to begin laser processing.
The Universal software should be set to automatically focus based on the material thickness specified.
Order of execution when using the materials database tab proceeds with raster objects first, then vector marking objects and finally vector cutting objects.
Test Cuts First
It is not guaranteed that the laser will successfully cut through a material. It’s recommended to do a quick test cut:
Create a very small shape (such as a ½" - ¾” diameter circle) and position it in a marginal part of your material or another piece of the same material.
Cut the test geometry. As always, watch for anything
On the UCP, click “Settings” to re-open cut settings.
Adjust the intensity sliders on the top right but increase by small increments.
Then move the test cut shape in order to repeat.
Here are some general tolerancing tips, picked up from work experience, in no particular order. Anyone is welcome to add to these or correct them if you see something inaccurate.
Tolerances should always be as large as possible for the part to still function
Overly tight tolerances are expensive, time consuming, and unnecessary
3D printed parts will shrink. A lot.
Online estimates are ~8% for ABS and ~3% for PLA but the actual amount will vary drastically based on the printer, settings, and the part itself.
If possible, part corners should be chamfered or filleted, especially for sharp/hard materials
For machined parts, a surface finish of 125 microinches (3.175 micrometers) is standard
Any holes to be tapped should be first made one size smaller than the tap size
I.e. for a #6 screw, one should drill a #5 hole before tapping with a #6 tap
Holes should be larger than the fasteners that go in them. The smallest diameters for a "normal" fit by ASME standards are listed below.
See ASME standard 18.2.8 for more information, or go to:
GD&T should be added at some point
When you have money but you'd rather have raw material, fasteners, and other fun things
Check out the page if you're not sure what you want.
Jacobs sells at-cost and is often the best option available. Most commonly, plywood for laser cutting and 1/8" and 1/4" 6061 aluminum sheets are cheaper here than anywhere else.
Would you like some Delrin? Lexan? ePlastics is pretty cheap and easy to order from on-line. Would recommend.
If you need any 8020 extrusions or parts, this is the place to go. They give a 10% discount, but they sadly don't do sponsorships. They can also give
some design advice and they can answer more specific questions about 8020 that can't be answered on the website (you can also search the catalog)! Michael and Benson have been in contact with David Morton from there. His email is david.morton@tecotechnology.com
Good customer service, highly recommend.
Screws, bolts, washers, nuts, threaded rods, tooling, some stock, and similar are the most common purchases from McMaster. Many other parts (gears, linear bearings, pumps, etc.) are available but may be prohibitively expensive.
If you need pipe fittings, valves, regulators, or really anything for propulsion, Swagelok is our go-to supplier.
Buy components from Digikey. Really everything should come from here.
If you can't find it on Digikey, maybe you can find it here?
Apparently Arrow is actually the largest supplier of these three by volume, so you should probably be able to find it here if not at the other two.
How to make those cool parts that you designed; or, how to design cool parts that are make-able
Broadly speaking, this section covers how to select materials, how to manufacture parts out of stock, and how to choose / work with parts that you cannot manufacture yourself.
If you're just getting started, we recommend going through the 3D Printing and Laser cutting tutorials; refer to the Material Properties and Uses page as needed:
If you have more experience or are a little farther along in the design process, check out some of our other tutorials on how to use commercial parts or where to source stock from:
For more specialized needs, we have a few tutorials on more advanced manufacturing methods:
80/20 Inc. has a fantastic website detailing a lot of information about their extrusions.
This page is intended to serve as a summary and introduction to these extrusions.
The most useful part of this page is probably the Tips and Tricks section at the bottom.
8020 is a brand of Aluminum extrusions. "Extrusions" just means that they are parts with a constant cross section that are extruded through a dye in their manufacturing process. 8020 sells an entire product ecosystem that revolves around their "T-slot" extrusions. Their cross section looks like this:
8020 parts are often used to build frames and other equipment quickly and more conveniently than alternatives (such as welding, manufacturing custom parts, etc.). They are widely used in industry for several reasons:
They are easy and convenient to use
While they can be pricey, they are high quality and are usually cheaper than a custom solution
They are very versatile and can be used for many types of applications
They can be expanded to include linear motion bearings, stanchions, guard railings, fences, etc.
The basic principle behind fastening 8020 extrusions is called the "2 degree drop lock"
The main idea here is that the edges of the extrusions are not perfectly parallel to each other, but rather offset by 2 degrees (this can be a pain in SW sometimes, be aware). When a fastener is tightened, it elastically deforms the extrusion, creating a strong normal force on the nut and fastener head. This normal force allows for a large static friction force to be applied, securing the nut in place.
For reference, on of these fasteners can usually hold up to several hundred pounds when installed properly.
8020 has a lot of options, which is fantastic. However, this can be intimidating for first-time users. This guide is intended to help you through selecting 8020 components for your assembly
For most applications at STAR, we do not use metric extrusions or fasteners. This leaves you with two choices for the extrusion series:
1010 - This is a 1" x 1" extrusion. This will usually be enough for most applications where the structure is not under significant or mission critical load.
1515 - This is a 1.5" x 1.5" extrusion. This is the maximum imperial sized extrusion, and is used for more "beefy" structures.
Extrusions are also available in non-square shapes. For example, a 1530 extrusion will measure 1.5" by 3", indicating that it is essentially two 1515 extrusions connected side by side. These are still compatible with other extrusions in their series
Note that for each of these extrusions, there are submodels such as "1515-S-Black-FB". These indicate unique features of the extrusion. Be mindful of these, since they can at times compromise strength or offer options for weight reduction. There are countless options, but these are a few to be aware of:
S indicates a smooth finish
Lite indicates a lighter but weaker profile. Lite gets abbreviated to L if there are other modifiers (about 22% lighter than regular
UL stands for ultra light (about 12% lighter than L, 32% lighter than regular)
Black indicates a black anodized finish. More expensive, questionably more corrosion resistant.
Fasteners are an integral part of 8020 product selection. The 8020 catalog provides a good amount of detail on the differences between fasteners, and their youtube channel is also recommended for seeing how these work in action.
There are several questions to keep in mind when selecting a fastener:
How strong will the fasteners be?
How much machining will be necessary on the profiles?
We can order parts pre-machined, but it does cost more money. Machining parts ourselves is also possible, but is very time-intensive.
How often will this fastener need to be removed? Will it need to be removed after the assembly is assembled?
What are the loads going to be on the fasteners?
A force applied perpendicular to the T-slot and the axis of the screw will differ greatly from a force applied along the T-slot, which will both be very different from a torque in the axis of the screw.
For small orders, 8020.net is fine. For larger orders, please email David at TECO technologies.
Don't make the same mistakes we did.
PLEASE PLEASE PLEASE if your budget permits order parts pre-cut and pre-machined. It saves a lot of headache on our side, and the whole point of 8020 is that it's easy.
If your budget does not permit, reconsider your budget. Machining and cutting 8020 for an average-sized project will take well over 10 hours in the machine shop for the average student.
If you've reconsidered your budget and still can't afford, buy extra length of 8020, since cutting and mistakes will eat up your length. Also order extra fasteners
Try to stick with flat plates and gussets. Anchor fasteners are difficult to access and expensive, and end fasteners require tapping into the aluminum, which isn't ideal for things that need to be disassembled frequently. 45 degree supports are also very nice for high-strength applications.
When tightening fasteners, you almost can't go too tight. Most people will not tighten the fasteners enough to engage the 2-degree drop lock on the first try.
Think about accessing fasteners when you create your assembly. A fastener is no good if you can't get in with a hex wrench to tighten it.
Be mindful about constraining these, since the 2-degree drop lock means that seemingly parallel planes are not actually parallel
8020 becomes very useful when you interface it with your custom parts. This is not very difficult to do, and essentially just involves including an equivalent flat plate fastener in your part.
A way to selectively remove material from a piece of stock
Contrary to popular belief, a mill is not a drill press. This is a manual mill:
A mill has a spindle which holds an end mill. End mills are similar in appearance to drill bits, but are not the same!
The spindle spins the end mill rapidly while the material (or the spindle) is moved in the x, y, or z directions. More advanced, usually computer numerical control (CNC) machines can also sometimes rotate, giving up to 4 or 5 "axes" to move in. With CNC milling, a computer, rather than a human machinist, handles the motion of the stock and spindle. Here is an example of a CNC mill in action:
Both manual mills and CNC mills generally share some basics in terms of how they operate. Here is a video that covers the basics of mills:
Just like drill presses, mills can make holes in materials. You can either use an end mill, or simply put a standard drill bit in the mill using a removable chuck. Mills are particularly useful if you would like a set of very precisely spaced holes, as they possess an x-y coordinate system (drill presses generally do not).
In the image above, notice that the center hole is not bored all the way through. This is generally possible to do fairly accurately even on a manual mill, with the use of a stop. However, dimensional accuracy may vary. Always check with your machinist first.
In the US, drills come in number sizes (smallest useful size being #50-#60 and going all the way up to #1, which is roughly 0.228 in) as well as letter sizes, which start at A (0.234 in) up to Z (0.413). Beyond and interspersed with the letter and number drills are standard fractional inch size, ranging commonly from as small as 3/64 in up to 1 1/2 in. Check with your machinist to see what sizes are available first.
A mill can remove material from a face or create a flat surface at any depth. Furthermore, sharp corners are possible if the tool is allowed to travel off the end of the part (see Pockets section for examples of when this is not the case). It is best if these cuts are at right angles to each other; more complex geometry will require the use of CNC.
For an example video of a CNC machine cutting a more complex profile, see below:
When a flat surface with some type of wall on the sides is desired, we have a pocket. Mills are able to do pockets, but keep a few things in mind:
End mills (the tool) have finite radii. For example, if an 1/8" diameter end mill is used to make a pocket, the interior corners will have a minimum 1/16" radius. Use a fillet in CAD to reflect this.
Conventional (manual) mills may not easily be able to make, for example, a rectangular pocket with precise corner coordinates, especially if the pocket is deep and requires multiple passes. This type of geometry is better suited for a function mill or a CNC mill. When in doubt, check what can and cannot be done with the person who will be making the part!
This type of geometry will generally only be possible with a CNC mill. Please be aware that CNC parts can have long lead times if coming from the machine shop. Furthermore, there are still limitations on what a CNC machine can do; as with manual mills, there are limits based on available tooling (curved surfaces generally require ball end mills) and the material.
Try to limit the number of different tools needed to make your part. Tool changes can cost significant time and effort. For example, try making all holes a standard diameter, or choose just a few. If a pocket is large, use large-radius fillets on the corners to allow the machinist to use a single large tool to make the feature in one pass, rather than switching to a smaller tool just for the corners.
When in doubt, ask. Other club members or the machine shop staff are happy to help!
Shoutout to Dennis K. Lieu
Coarse threads are the most commonly available and should be suitable for almost all use cases
Before choosing to use metric threads, please coordinate with you project team to ensure the type of thread used is consistent.
When working on a project or part, try to minimize the number of different sizes of screws used. Avoid having a variety of screw sizes.
Try to keep screw drive type consistent.
Use the clearance hole chart in the "Tolerancing" page for appropriate clearence hole sizes.
Be mindful of the size of the screw head when designing a part, especially of how the head affects clearance to other parts. It can be useful to obtain the SolidWorks model of a specific screw (commonly avaliable on McMaster) to check for clearance issues.
Screws used as a hinge, such as part of a screw-nut hinge combination, and other structural-critical screws should have an appropriate thread locker (such as Loctite 242) applied.
Screws and standoffs used in close proximity to exposed electronics should ideally be non-conductive.
Always make sure the nut you get corresponds with the thread of the screw that you are planning on using it with.
The most common type of nut that we use is a hex nut.
Nylock nuts are the common alternative if a more secure connection needs to be made.
In nearly every case, nuts require much more clearance than screws and thus are usually oriented away from moving parts and where they can't come into contact with other surfaces.
Threaded inserts can be extremely useful way of having a threaded connection in your designs.
A very common situation that can arise is a need to thread into 3D printed parts. 3D-printed parts are difficult to tap (use a tool to create threads on the inside of a hole) because plastics (especially for PLA) deform at low temperatures. 3D-printing internal threads are also difficult because of the need for high precision. Directly threading a screw into a part is often not ideal, because repeatedly removing and screwing the fastener will appreciably lower the integrity and strength of the connection.
As such, threaded inserts are an ideal solution to this issue, since the insert is designed to be permanently secured to the part yet also allow for the repeated insertion of a screw into the thread. An analogous way of achieving this is to design the part to hold a captive hex or square nut inside. In this case, the nut acts as the insert. More information about plastic-specific inserts can be found here:
Another common situation is a need for a thread into a soft metal, such as aluminum. Aluminum is often desirable, especially for aerospace applications, because of its low weight. However, it is not ideal to directly thread into aluminum for the following reasons:
Most fasteners are steel, which is considerably stronger than aluminum. A threaded interface between steel and aluminum can cause significant wear to the internal threads of the aluminum leading to issues such including binding.
For a reference on dimensions on mil-spec threaded inserts, see the below documents:
Rivets are permanently-deforming fasteners. Please do not use rivets unless you have a very good reason to do so, as they prevent the disassembly of the part (without an angle grinder). There is little information on rivets included here on purpose. Rivnuts or Nutserts are slightly better, but also have issues related to their deformation.
Costs at least at Jacobs; parts are free
Glass transition at a slightly higher temperature (~ higher)
.
*
These parameters are specified in the laser cutter preferences interface by one of two methods. The two methods are laid out in tabs in the laser cutter interface. The first method is a materials database method which simplifies setup for beginners and casual users, the second method is a manual method with allows much more control for advanced users. Each method treats assignment of laser job settings to colors in the graphic being printed and interpretation of raster and vector elements in the graphic being printed in slightly different ways.
It will load the geometry into this screen.
.
*
These parameters are specified in the laser cutter preferences interface by one of two methods. The two methods are laid out in tabs in the laser cutter interface. The first method is a materials database method which simplifies setup for beginners and casual users, the second method is a manual method with allows much more control for advanced users. Each method treats assignment of laser job settings to colors in the graphic being printed and interpretation of raster and vector elements in the graphic being printed in slightly different ways.
It will load the geometry into this screen.
When creating 8020 assemblies in SolidWorks, use the models provided on 3D Content Central ()
When it comes to sizing holes, make sure that there is actually a drill bit or end mill with the correct diameter for your hole. Perform a google search for a drill bit sizing chart or see the table here: for a conversion between letter and number drill bits to decimal inches.
That being said, there are some parts that are great candidates for CNC and it can certainly be a useful technology. Small parts especially will be easier to make (see: ) and can make design significantly easier.
As a general rule, simple geometry is better. Things like right angles and low requirements for accuracy and precision (see: ) make everyone's lives easier.
For a more in-depth treatment, refer to this fastener handout:
If working in US customary units, refer also to the Wikipedia page on the Unified Thread Standard: If working in SI units, refer to the ISO thread sizing Wikipedia page:
can always be of concern when joining two dissimilar metals.
Again, threaded fasteners or captive nuts are ideal in this scenario. When choosing inserts for aluminum, make sure they are passivated or mil-spec, as to prevent galvanic corrosion from occurring. can be ideal for this application.
Designation
Nom. (in)
Nom. (mm)
Min. (in)
Min. (mm)
#0
0.060
1.524
0.076
1.930
M1.6
0.063
1.600
0.071
1.800
#1
0.073
1.854
0.089
2.261
M2.0
0.079
2.000
0.094
2.400
#2
0.086
2.184
0.102
2.591
M2.5
0.098
2.500
0.114
2.900
#3
0.099
2.515
0.116
2.946
#4
0.112
2.845
0.128
3.251
M3.0
0.118
3.000
0.134
3.400
#5
0.125
3.175
0.156
3.962
#6
0.138
3.505
0.170
4.318
M4.0
0.157
4.000
0.177
4.500
#8
0.164
4.166
0.196
4.978
#10
0.190
4.826
0.221
5.613
M5.0
0.197
5.000
0.217
5.500
#12
0.216
5.486
N/A
N/A
M6.0
0.236
6.000
0.260
6.600
1/4"
0.250
6.350
0.281
7.137
M8.0
0.315
8.000
0.354
9.000
CalSTAR Composites Best Practices
This technical note condenses practical knowledge about producing composite parts from the CalSTAR team and alumni. Focus is on materials and best practices: what to use, where to get it, and how to use it. This document is not a replacement for hands-on practice and self-driven learning, but it should give newer team members a good head start.
Unlike a typical engineering note, this document is a living article with no restricted author list and no formal revision structure. Therefore, when editing, please be concise, neutral, and specific. This document is a forum for imparting hard-won composites knowledge, rather than hard-won personal philosophy. With the exception of diatribes against Bondo. These are fair game.
Use good safety practices (gloves, goggles, avoid skin contact, ingestion, inhalation, etc) with all resins and materials described below. Read the MSDS and be aware of safe disposal methods as well as safe use. This document makes no attempt at a complete description of safe handling or risks of the materials described. Some particular examples of the safety precautions to be aware of are:
Again, it is essential to properly research for yourself the risks and best safety practices for each material and process before use. If you are unsure, it is always better to contact a lead and ask for assistance than to endanger yourself.
Resins are usually used with a reinforcing fiber or filler. Common resins fall into the categories of epoxies, polyesters, vinyl esters, and cyanate esters. Most layups generally use:
Cyanate esters behave similarly to epoxies, and are the most common resin system for prepreg.
Understand that all vinyl esters and polyesters require fitted working respirators, to avoid breathing in the solvents, this should be done with zero ex
Also understand that vinyl esters and polyesters should only be used in conditions with good ventilation and no spark / fire hazard, as the aerosols are flammable.
Many dusts and fillers are bad to breathe -- when in doubt wear a dust mask.
If material like a resin gets on the skin, it is usually incorrect to attempt to “wash” it off with a solvent. The reasoning is that the solvent will simply dissolve the material and make it easier to penetrate the skin! Use soap and water with manual scrubbing instead.
epoxy as the matrix for fiber-reinforced laminates
vinyl ester as the matrix for fiberglass molds
polyester (e.g. gel coat) as the hard surface coat for molds – if molds are used.
These resins are all thermosets. In other words, the curing process is a 3D chemical cross-linking, where the mers (short CH molecules of which the resin is composed) grow strong links to one another. The process is both heat-driven and exothermic, so it accelerates itself. This means two things:
You can speed up a cure by heating the resin.
Thinly spread resin (volume / surface area = low) will cure much more slowly than a mass of resin in a container (volume / surface area = high).
With regard to point (2), a large mass of curing resin left in a cup will often turn brown, smoke, and put off foul smells and lots of heat. (The self-accelerating effect is compounded by the fact that polymers have low thermal conductivities, so the heat cannot escape the curing resin easily.) Therefore always dispose of excess resin by spreading it over a large area of paper or plastic, and letting it cure in that spread-out state.
The 105 epoxy system is the default for laminated parts. Various hardeners can be combined with 105 resin to adjust cure time and cured part properties. Usually the 209 hardener is chosen, which gives a long pot life, so that the layup will not be rushed. The 105 system features a low viscosity, making it a good laminating resin. The main downside of the 105 system is its low Tg (~120°F).
9396 is one of the stiffest and most temperature-resilient (service temperature up to 350°F) structural epoxies. It is more difficult to use in laminations due to having a higher viscosity and shorter pot life than West System 105/209. (However, the team has made many successful laminations with 9396.) It can be used as a good adhesive, and is the best option for laminates or bonds in close proximity to intense heat sources (like the exhaust). 9396 is effective as a potting and repair resin. Expect working life on the order of 1.5 hours, and at room temperature, 70% cure in 24 hours, with full cure in several days. At elevated temperature (~135°F), cure time can be significantly reduced to ~1.5 hours.
Tap’s 4:1 epoxy is moderately stiff and strong. It has the benefit of being readily purchased on short notice, and can be used for general purpose potting and lamination. However, as a general purpose resin it makes significant compromises: it has a higher viscosity than 105 and a shorter pot life than both 105 and 9396. Expect a working life of less than 15 minutes.
The team has usually used Tap’s polyester resin, and found it serviceable. Polyester alone can be used as a matrix for fiberglass molds, and finds few other applications. In fact, other Berkeley teams have frequently used vinyl ester instead of polyester for fiberglass molds, since the vinyl ester is more thermally stable and bonds better to epoxy than polyester.
A polyester product called “gel coat” comes pre-filled with talc, CaCO₃, and other mineral oxides so that it can produce a thin, hard surface layer in molds. Tap’s gel coat has most frequently been used by the team for fiberglass molds. For surfacing of urethane foam plugs, a similar product called Duratec is probably superior in hardness and in holding a smooth surface during sanding; in a pinch gel coat on urethane may suffice.
Vinyl ester is very similar to polyester in processing behavior. It is somewhat more expensive than polyester, but deforms less under temperature and bonds well to both polyester and epoxy. Vinyl ester is the usual choice of matrix for fiberglass molds – this because fiberglass can be more demanding of a perfect medium for a usable quality layup. Tap’s vinyl ester product has generally been used.
Cyanate ester is the most common resin system for prepregs (frozen fiber tapes pre-impregnated with resin). Once cured, it is mechanically similar to epoxy, but has better resistance to hot-wet conditions. In the uncured state it is very sensitive to moisture. When removing prepreg from the freezer, where it should be stored prior, it must be allowed to come to room temperature before opening the bag. Otherwise condensation on the material will ruin it. When repacking prepreg for putting back into the freezer, include a dessicant pack and seal the bag well. Cyanate ester systems require heat to properly cure. Most of the prepreg we will likely use is RS3, and cures when held at 350°F for several hours. There are published schedules of heat and pressure to define good cure cycles for various resin systems.
For the most part, the team has used high-strength carbon fibers such as AS4 and IM7. These have relatively low modulus and fall into the “black aluminum” design regime. A key decision when acquiring fiber is the form of the fabric: whether to get unidirectional or woven, and if woven, what type of weave. It has been useful to get a moderate amount of unidirectional material for making strength-controlled shear panels, but for the majority of parts that are not filament wound, we will use woven cloth.
Satin or twill weaves are much easier to control during layup than plain weave. Plain weave is very difficult to use in any part with bi-directional curvature or uni-directional curvature tighter than ~200 mm radius. Therefore it is advisable to always insist on 5 harness satin or twill. Fiber areal weight of ~6 oz/yd² is generally useful. In special applications, lighter fabrics may be desirable.
Carbon fiber composites have good electrical conductivity in the plane of the laminate, but if using the carbon for example as a grounding body, it is necessary to drill into it and install a metal stud which will bypass the current past the surface epoxy (which is non-conductive) and into the center of the laminate, where contact can be made with the exposed carbon fibers. Carbon fabrics are easily cut with good, sharp shears.
By experimentation, we have found that plain weave final product should be around 0.35-0.36 g per square inch.
The usual glass in fiberglass fabrics is E-glass, which is strong and moderately stiff. Fiberglass is good as a thermal and electrical insulator and is reasonably strong, but significantly heavier and less stiff than carbon. Many weights of cloth are available depending on the application. Usually a fiberglass mold is made using glass mat and vinyl ester resin; however, in the case of an epoxy-glass mold, one would use a woven glass fabric. Glass fabrics are easily cut with good shears.
Aramids (commonly referred to by the brand name “Kevlar”) are strong in tension and moderately stiff. They have extremely poor strength in compression, but extremely high strength in shear. They are therefore used where skid-protection or shrapnel containment is necessary. They find some use in the lining of section of rocket airframe where catastrophic failure which may result in shrapnel may be present. Aramids are difficult to cut in the dry state and difficult to cleanly trim or machine when cured in a matrix. In the dry state, the best method of cutting is with well-sharpened high-quality shears, and patience.
The team has experimented before with fabrics that combine both carbon and aramid fibers in the weave. Generally this hasn’t been found particularly useful, as the aramids reduce the overall stiffness and compressive strength without adding any benefit that couldn’t be otherwise more efficiently achieved by including a separate aramid layer in the stackup.
Glass fibers and carbon fibers are also produced in mat form, where the fibers are randomly oriented and loosely packed together. The fibers are lightly bound to each other by a “size” adhesive, which dissolves in the resin upon lamination. Glass mat fibers typically have a size which is soluble in polyester and vinyl ester, but has poor solubility in epoxy. Carbon mats usually get a size which has better solubility in epoxy. But the type of size can only be definitely ascertained by contacting the manufacturer. Glass mat in heavier weights (1.5+ oz/yd²) is predominantly used in combination with vinyl ester when making fiberglass molds. In low weights, glass and carbon mats are usually called “tissues” or “surfacing veils”, and are useful when a very smooth surface is required on a part without the use of gel coat. As an example, an 0.7 oz/yd² glass surfacing veil has been used for the interior surface of the restrictor; weights down to 0.3 oz/yd² are readily available.
There is not much "theory" to selection of weave in typical rocketry usage. One usually wants twill or satin weave, and not plain. Plain weave is difficult to use on anything other than flat plates or large cylinders. Twill or satin will conform to bi-directional curves much better. Satin is most generally useful, especially in harnesses 5HS to 8HS. The tow count -- 1k, 3k, etc -- often seen associated with a weave is the number of fiber strands in each tow of the weave (a tow is a single fiber bundle -- multiple tows are woven to form a weave). So the tow count is directly related to the fiber areal weight. (Fiber areal weight -- FAW -- is the mass of fiber per unit area, usually quoted in oz/yd² or g/m². The unit g/m² is often written “gsm”.)
Fumed silica (also known by brand name “cab-o-sil”) is a filler powder used to thicken epoxy resins. It is lightweight and confers thixotropic (shear thickening) properties on the resin, making it very useful in all potting, filling, and surfacing applications. Epoxy filled with fumed silica creates a hard, sandable surface. Sometimes microballoons are added to either reduce weight or weaken the surface (to make sanding a little easier).
Glass microballoons are a powder consisting of small hollow glass spheres. The hollowness makes them extremely lightweight. They are useful in potting applications where weight minimization is important. Microballoons are not as strong as fumed silica, and do not thicken the resin as effectively, therefore they are often used in combination with fumed silica.
Talc powder (a magnesium silicate) can be used as an epoxy filler. It is heavier than fumed silica and makes a surface which can be very difficult to sand. Therefore, it is not commonly used in applications where a surface finish is desired. However, it does improve smoothness of the filled resin, so sometimes a small amount of talc may be added in a surfacing application.
Milled or chopped glass fibers are readily available. They are simply E-glass fibers which have been cut to very short lengths. Milled fibers are short enough to look like powder, but will significantly strengthen the resin when used as a filler (at a cost of more weight). Chopped fibers are usually ⅛” to ¼” long, and greatly strengthen the resin, but it is difficult to spread a resin smoothly when filled with chopped fibers. Therefore, milled fibers are more often useful, particularly as an additive in mold surfacing when high strength is required (at the cost of more sanding time). The CalSTAR team has utilized this in the past by impregnating JB weld adhesive with Carbon Fiber shavings.
Chopped carbon fibers are usually produced by the team, simply by repeatedly cutting scrap carbon fabric. They are useful for rapid repair in potting and filling applications. When onsite during a test or launch day, it is useful to have on hand a quantity of chopped carbon and fast-curing epoxy, to rapidly mix up a high-strength potting compound to apply to fill damaged areas which will cure within a short time period. Resin filled with chopped carbon can be difficult and messy to control, as the fibers tend to clump together and not flow.
Bondo is a well-known material among hobbyists and amateurs. It is notable for being weak, brittle, and difficult to control. In particular, its cure time and hardness is highly sensitive to mix ratio with the catalyst. When applied as a filler to a mold surface, the Bondo is much weaker than the rest of the surface; this discontinuity in strengths makes it difficult to achieve a smooth and continuous surface during sanding. Bondo is composed of a polyester resin with a weak filler powder, and will dissolve styrene foams. No one knows precisely why Bondo remains popular, but year after year its ill-advised usage has punished the production schedule of many rocketry and other competition teams alike. It is strongly recommended that Bondo not be used.
Special dispensation is made for a particular Bondo product called “Professional Glazing & Spot Putty”. It has a finer grained filler than general Bondo, and can be useful in the single specific case where one wants to fill tiny pinholes in mold surfaces -- in this case the goal is explicitly to have a weak filling agent, so that any excess filler remaining on the surface surrounding the hole can be easily sanded off later with a fine paper, and not risk damaging or mis-shaping the rest of the surface. A common mistake is to forget that the filler is a two-part system: it must be mixed with a hardening catalyst in order to cure. UV-curing putty is available, but it can be difficult to achieve full and consistent cure; therefore, the UV-curing material is also not recommended.
Urethane foam is the standard for mold making. In general, the higher the density, the better will be the mold. Cost scales directly with density; there are trade-offs to be made. Typical densities availale are 6, 10, 20 lb/ft^3. High quality parts have been made with 6 lb/ft^3 foam, but 10 or greater is preferred, as it will improve fidelity and reduce the coating/sanding effort considerably.
Urethane foam sands well and is reasonably strong. In lower density (6 lb/ft^3) take care not to puncture the foam, as its compressive strength isn’t too high. The foam is somewhat brittle and should not be dropped from too high or danced upon too enthusiastically. Urethane foam is compatible with both epoxy and ester resins. Slabs may be bonded together with either of these agents, or urethane Liquid Nails, or Gorilla Glue. When bonding slabs, make the adhesive layer as thin as possible -- otherwise it will be a hardness discontinuity that interferes with machining/sanding.
Polystyrene foams are cheap and readily available. They usually come in 1” thick boards meant for building insulation, but can be sometimes purchased thicker. There are two basic types:
● Expanded polystyrene (EPS)
● Extruded polystyrene (XPS)
EPS is composed of many beads fused together, and is horrible to sand / mill / shape. It is usually white, and often used in molded shipping boxes or packing peanuts. XPS is much better for sanding and shaping, and comes in colors blue or pink (there is no significant difference between XPS in the two different colors). Both typically come in 1-2 lb/ft^3 density: very light and very low hardness.
Over the years, polystyrene has been used to make a number of molds for FSAE and CalSol, two other competition teams on campus. These generally have been of low quality and time-consuming to produce. Polystyrene has the twin disadvantages of being very difficult to sand smooth, while also being incompatible with all polyester resins / fillers (these resins include styrene monomers in their formulation -- clearly, then they will dissolve styrene foam).
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For the most part, one uses special epoxy formulations for adhering composite parts.
9309 is a high-strength structural epoxy adhesive. It is similar in many respects to 9396, but has a special filler allowing it to bridge gaps up to 0.030” and create good fillets with honeycomb core. It has a lower glass transition temperature than 9396, therefore it can be debonded with a heated blade when necessary. One generally does not add extra fillers to 9309. It has a Tg = 130°F and service temperature up to 160°F.
DP4X0 is a high-strength epoxy adhesive with a minute pot life indicated by the value of x and 24 hrs to full cure. Pot life options include 20 minutes, 60 minutes and 90 minutes. Recommended for all general purpose bonding when fast cure time is desired. Excellent for trackside repairs. While it can be filled with milled or chopped fibers to increase strength of a repair patch, this may make it brittle and thus more prone to failure. It also comes in a "NS" or "non-sag" variant which is good for applications such as creating fin fillets.
9396 is discussed earlier in this document as a laminating and potting resin, but is repeated here. It is specifically useful as an adhesive in high-temperature locations (service temperature up to 350°F). It can be moderately filled with fumed silica to bridge bond gaps between 0.020” - 0.030”, and needs no filler at gaps less than 0.015”. Because 9396 is quite linearly rigid, a good bond joint design becomes more important wherever peel failure is a concern. As one of the stiffest resins available, with reasonably low viscosity, 9396 is particularly good as an adhesive whenever the primary design requirement is stiffness and a definite 0.005” - 0.008” bond gap can be obtained.
Decent results can be achieved with adhesive epoxies available from hardware stores. Devcon brand epoxies have been used successfully and are recommended. However, 9309 or DP420 will still be superior in strength, stiffness, and repeatability.
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Shears are not scissors. Shears look like big scissors, but they’re better. Good shears are sometimes marketed as carpet and upholstery shears. They have an adjustable pivot screw to control pressure between the two blades. The blades are of alloy steel and hold an edge. Shears need to be sharpened from time to time. Correct sharpening technique is essential to maintain close contact between the two shearing edges. An example of good shears is shown from the MSC catalog below.
The most effective saws for cutting fiber composites tend to be toothless steel disks impregnated with diamond powder. These are commonly available, marketed as tile-cutting saws. They can be purchased in sizes which fit Dremels, grinders, tables, etc.
High-speed steel drill bits will go dull fairly quickly when cutting fiber composites. Cheap ones can be sacrificed for simply punching holes. Machinists will not thank you for using their good precision drills to cut composites. Carbide bits are preferred, as they will last longer and cut cleaner. High precision (diameter tolerance < 0.001”) holes are readily achievable in composites with carbide reamers.
If a composite part is to be cut or shaped in a mill or router, the cutter should preferably be carbide, with a titanium nitride coating. Again, machinists will not thank you for dulling down their general-purpose high-speed steel cutters on composites. Sacrificial bits may be used to ease their pain with prior request to the team.
A standard stock of sand paper includes 60, 100, and 200 grits in dry sanding paper; 100, 200, 400, 600, 800, 1200 in wet sanding paper. Higher grits go dull quickly; in any grit, the paper must be replaced with some frequency as it goes dull. Discard dull paper -- this is not the place to be miserly.
Scotch-brite pads come color-coded in different levels of aggressiveness of abrasion. It is usual to keep a stock of green pads (aggressive) and light gray pads (very soft). Note that some other colors of scotch brite are “tan”, “gray”, and “dark gray” -- not to be confused with “light gray”, which is almost white in color. Like sand paper, scotch-brite goes dull with continued use, and should be discarded.
Single edge razor blades find innumerable uses in composites manufacture. They are cheap and disposable. It is usually worth the extra money to get precision edge stainless blades, which will hold an edge sharper and longer than the standard blades. Blades should be disposed of frequently as they go dull. Proper disposal requires a sharps box of some sort.
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Before bonding two surfaces together, it is critical that they be properly prepared. The goal is to achieve three qualities:
Cleanness -- no interfering grit or organic particles
High surface area -- increase surface area with texture
High surface energy -- increase the molecular adhesion between the surface and the glue
When bonding a fiber composite surface, the goal is to achieve scratches in all directions in the plastic matrix only. Carbon fibers, in particular, are poor bond surfaces, therefore one does not want to sand into the fiber. (If you see black grit, you’ve gone too deep.) Green scotch-brite pads are an effective abrasive to achieve scratches in the matrix without attacking the fibers underneath. Scratch the surface thoroughly in all directions, either with swirling motions ~1” in diameter, or by scratching at 0°, 90°, +45°, -45° in succession.
When bonding a metal surface, sand paper may be necessary to achieve good scratching. 200 grit dry sanding is effective, again moving either in 1” swirls or a 0°, 90°, +45°, -45° succession of sanding directions.
Clean the surface well with degreaser and water, then isopropyl alcohol. For stubborn surfaces, acetone may be necessary, always check to ensure that the surface is acetone safe before using acetone.
Prior to bonding, the quality of the surfaces can be tested by putting a few droplets of water on them. If the water spreads out into a thin film, then the surface energy of the part well exceeds the surface tension of the water. This is a good sign, indicating that high surface energy has been achieved, and the bond will be good. If the water balls up, repelled from the surface, then the surface prep steps must be repeated.
Bare aluminum in air rapidly forms an oxide layer which bonds poorly. However, if this natural oxide layer is replaced with a special chromate one, the aluminum-to-epoxy bonds is one of the strongest you can get. Therefore, after mechanical abrasion and cleaning, the aluminum is to be etched with West System 860. While still wet after etching, the second part of the 860 system is applied, which puts down a chromate layer. This protects the aluminum surface from oxidation for several hours. In this time window, the bond should be made. A respirator with good filters is recommended while applying the chromate.
Note that anodized aluminum is a very poor bonding surface, and should be completely removed. This can be time consuming.
Also note that there is a more permanent alternative to West System 860, called “iridite” or “alodine”. This surface coating makes for excellent bonds, and does not have the same restriction on time frame for bonding. (The alodined surface is good for adhering to paint as well as epoxies.)
When the goal is to have a material not stick to a surface (i.e. a plug or mold), it is again critical that the surface be properly prepared. The goal is to achieve three qualities:
Cleanness -- no interfering grit or sticky particles
Low surface area -- keep the surface as smooth as possible, i.e. a mirror-finish
Low surface energy -- decrease the molecular adhesion to the surface
Flash from previous uses of the mold should they be present, should be mechanically removed. A soft scotch-brite pad (light gray) is helpful. Be sure not to scratch the mold. If aggressive cleaning is necessary, use a degreaser with water, then acetone. Otherwise use isopropyl alcohol with a towel. Blow off dust and repeat wipe-down until thoroughly cleaned.
In situations where a mold is not used, but you are interfacing a carbon fiber layup with a surface which eventually you do not want the carbon to be bonded to, following the same steps as above but replacing the mold with your surface. Remember that it is always better to be sure of what you’re doing but slower than to work quickly and risk damaging or destroying the surface.
Use Meguiar’s mold release wax or Part-all paste wax. Apply a thin light layer over the whole surface with a microfiber towel. Let the solvents flash off 5 minutes, then buff in the wax until shiny with a clean microfiber. (Buffing well is important -- a shiny waxed surface will release well, whereas a hazy texture of wax can actually act as a mild adhesive!) Repeat a minimum of 3 coats. The mold release wax provides a strong, low surface energy barrier between the mold and the part. It fills and smooths pinholes and tiny scratches. Often, mold release wax only needs to be applied the first few times a mold is used -- after that, the mold becomes “seasoned”, with plenty of wax permanently impregnated into the surface.
Before applying mold release film, but after waxing, the quality of the release surface can be roughly observed by putting a few droplets of water on the surface. If the water balls up, then the surface tension of the water exceeds the surface energy of the mold. This is a good sign, indicating low surface energy has been achieved on the mold, and it should release well. If the water spreads out in a thin film, this means the surface must be improved, either by better waxing or (more likely) by stripping off the wax (with acetone) and sanding the surface smoother, then clean it again and re-wax.
Mold release film is applied every time a mold is used. It is applied as a thin liquid layer which hardens into a polymer film no more than a few microns thick. It provides a breakable layer and a geometric offset between the mold surface and the part, allowing for easier release. Dampen a towel with mold release and wipe on a single layer covering the full surface. Rewiping over an area will only dissolve the previous release and is therefore unnecessary, but not harmful. Again, understand that the mold release film is a very thin coat.
In a typical application, where a male plug is to be made, and then a female mold produced off of the plug, the essential steps are:
Urethane foam slabs are bonded together into a larger block
The foam is machined by a CNC routing shop off of CAD geometry
The machined plug is sprayed with a polyester-based hard surface coat (e.g. Duratec or Gel-Coat)
The coated plug is sanded smooth and polished
The female fiberglass mold is laid up on the plug
For a nosecone of size, say, 13” in diameter, expect step (1) to take two person-days, step (3) to take two person-days, and step (4) to take six person-days. The schedule for step (2) depends on how quickly you can get the CNC shop to mill the foam and send it back. Making the female mold (step 5) is discussed separately in this document. The bottom line to be very aware of is to start early! The time estimates above are deceiving, because:
● These estimates are for experienced workers. Students new to the process will be slower, with greater risk of damaging plugs and then needing to repair them.
● All curing processes have inherent downtime while you wait for resins to harden. This compounds the time cost of any unexpected repairs.
● The other time constraints on student schedules -- you really need full workdays to be most effective, and these only happen twice a week.
It is worth checking the mass of a given foam plug in CAD, to understand how many people will be needed to move it around as it goes through the various processing steps.
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The following outlines the process for making a 2-part fiberglass mold
Necessary Supplies:
● ⅛” Particle Board
● Thick Fiberglass Mat
● Vinyl Ester Resin / MEKP Catalyst
● Oil Based Clay
● Hot glue gun
● 2-3” paint brushes
● Plastic hemispheres
● Gel coat
Outline of steps:
Build dam separating the two halves of the mold
Gel goat first side
Lay-up fiberglass on first side
Tear down dam
Gel coat second side
Lay-up fiberglass on second side
Pull mold off plug
Outline of steps:
Prepare mold
Prepare materials: carbon plies, peel ply, breather, dropcloth, vacuum bag
Wet the carbon
SafeLease the mold
Lay up on mold surface
Vacuum seal part and vacuum part
Cure
Remove part from mold
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Some useful books and articles are compiled in the table below.
Title
Author
Where to find
Comments
ME127 reader: Design and Manufacture with Composite Materials
Multiple, compiled by Prof. Dharan
Needs to be Sourced
Concisely combines information from various textbooks and guides into one composites bible
Fiberglass and Composite Materials: an enthusiast’s guide
Forbes Aird
Purchase if need be – pdf is being sourced
Straightforward, covers all the basics in resins, fabrics, layups, tools, processes
Surface preparations for ensuring that the glue will stick in bonded composite structures
L.J. Hart-Smith
Search engineering articles database
Essential reading on bond prep of surfaces
Adhesively bonded joints for fibrous composite structures
L.J. Hart-Smith
Search engineering articles database
Essential reading on bond joint design and why bonds fail
Mil Handbook 17-2:
POLYMER MATRIX COMPOSITES
MATERIALS PROPERTIES
US Dept of Defense
Extensive list of tested material properties for various fibers and resins
Mil Handbook 17-3:
POLYMER MATRIX COMPOSITES
MATERIALS USAGE, DESIGN, AND ANALYSIS
US Dept of Defense
Overview of most practical composites matters. Most common standard reference in composites world
Handbook of Composites
edited by S.T. Peters
Good combination of theory and practical knowledge
Principles of Composite Material Mechanics
Ronald F. Gibson
at engineering library
Current ME 127 textbook, lots of theory
Tensile Properties of Glass Microballoon- Epoxy Resin Syntactic Foams
Nikhil Gupta and Ruslan Nagorny
Properties of epoxy-glass microballoon potting compounds
This is a rough and incomplete list of composites-specific suppliers that may be used.
Supplier
Location
Link
Comments
Tap Plastics
Stores throughout Bay Area, one close to garage
Close to RFS, fairly limited selection
The Composites Store
Southern California
ACP Composites
Livermore
Douglas & Sturgess
Richmond, close to garage
