# Tolerancing

* 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: [https://mechanicalc.com/reference/fastener-size-tables
    ](https://mechanicalc.com/reference/fastener-size-tables)

| 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** |

GD\&T should be added at some point