When thread milling, the cutting edge follows a larger circle than the tool center. To get the right feed at the thread, the programmed center feed must be scaled down for internal threads.
What the variables mean
| Symbol | Meaning |
|---|---|
| Center feed | Programmed feed at the tool center (IPM) |
| Edge feed | Desired feed at the cutting edge (IPM) |
| Dm | Thread major diameter (inches) |
| Dt | Thread mill cutter diameter (inches) |
Worked example
FAQ
Why would I thread mill instead of tap a hole? Thread milling avoids the risk of a broken tap stuck in an expensive part, works well in hard or work-hardening materials that are difficult to tap, and lets one tool cut multiple thread sizes by adjusting the toolpath.
Does thread milling take longer than tapping? Generally yes, per hole, since thread milling requires a helical interpolation toolpath rather than a single straight plunge, but the tradeoff is often worth it for larger threads, hard materials, or blind holes.
Run it instantly with the Thread Milling Feed calculator in Cutting & Tooling.