### Milling - Speeds & Feeds

# Machining Guide

## Basic Machining Tips for Engineering Plastics

- **Keep heat to a minimum** and ensure heat build-up in the part is avoided.
- **Keep tools sharp** at all times.
- Ensure that only the **cutting edge contacts** the material.
- Apply coolants (per guidelines) where heat is generated.
- The lower rigidity of plastics may require **support or plugging** to avoid deflection in thin-walled sections.
- Cutting tools should be **high-speed steel** or **carbide-tipped** for production runs, especially on graphite or glass-filled materials.

## Matching Tolerance

- It is much larger than for metal.
- Watch for **stress relieving** where a large body of material is removed.
- **Thermal conditioning** may be required after pre-machining on some parts.
- Allow a tolerance of **0.1-0.2% of nominal size**.
- Be aware of **thermal expansion** in larger parts or panels where fixings are required.
- **Minimum tolerance** for small dimensions: **0.05mm**.

| Endmill Diameter (Millimeters) | Surface Speed (SMM) | Feed Per Tooth (MMPT) |
|--------------------------------|---------------------|-----------------------|
| 3.175mm                         | 91-114 SMM          | 0.02286               |
| 6.350mm                         | 91-114 SMM          | 0.04572               |
| 12.700mm                        | 91-114 SMM          | 0.0889                |
| 15.875mm                        | 91-114 SMM          | 0.1143                |
| 19.05mm                         | 91-114 SMM          | 0.1397                |
| 25.4mm                          | 91-114 SMM          | 0.1778                |

| Endmill Diameter (inches) | Surface Speed (SFM) | Feed Per Tooth (IPT) |
|---------------------------|---------------------|----------------------|
| 1/8"                       | 300-375 SFM         | 0.0009               |
| 1/4"                       | 300-375 SFM         | 0.0018               |
| 1/2"                       | 300-375 SFM         | 0.0035               |
| 5/8"                       | 300-375 SFM         | 0.0045               |
| 3/4"                       | 300-375 SFM         | 0.0055               |
| 1"                         | 300-375 SFM         | 0.007                |

### References

- [Source: Feed Calculator](https://www.easyspeedsandfeeds.com/plastic)