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How to Cut Acme Threads on a Lathe
Guide · Updated October 28, 2026
Acme threads have a 29° included angle and flat crests and roots, which makes them strong for leadscrews and vises. Cutting them is like single-point V threads, but the tool has a ground flat on the tip and the cut is deeper, so it takes more passes and more care.
Check your mic first
Thread measurements are only as good as the mic. Check it against gage blocks before measuring pitch diameter. The free Gage Block Calculator builds the stack.
Step by step
- Grind the tool: Grind a 29° included form with a flat tip; check it in an Acme thread gage (fishtail).
- Set the flat width: For a general-purpose external thread the tip flat is about 0.3707 × pitch − 0.259 × clearance.
- Set tool height and square: Tool on center and squared to the work with the Acme gage.
- Set the gearbox: Select the TPI and confirm the pitch with a scratch pass.
- Feed the compound at 14.5°: Set the compound at half the thread angle and feed mostly with it, with small cross-slide moves to clean both flanks.
- Take many light passes: Acme cuts are wide; reduce depth per pass as you go deeper to avoid chatter.
- Check fit: Test with the mating nut, an Acme thread gage or three-wire measurement.
Worked example
For 1 in − 10 Acme (general purpose): pitch = 0.100 in. Basic depth is half the pitch, 0.050 in, plus 0.010 in clearance for 10 TPI and coarser, so total depth = 0.060 in. Tool flat = 0.3707 × 0.100 − 0.259 × 0.010 = 0.0345 in. Rough in passes of 0.006–0.008 in, falling to 0.002 in near full depth, then spring passes.
Acme vs V threads
Acme threads have a 29° angle instead of 60°, flat crests and roots, and a depth of about half the pitch. They carry heavy loads and wear well, which is why they show up on leadscrews, vises and jacks.
Common problems
Chatter means too wide a cut; lower the depth per pass and slow the spindle. A torn flank means you are cutting on both flanks; feed more with the compound. A tight nut usually means the pitch diameter is still large.
Tips
- V threads: cutting threads on a lathe.
- Internal: internal threads.
- Measuring: three-wire measurement.
FAQ
What angle is an Acme thread?
29° included, so the compound is set at 14.5°.
How deep is an Acme thread?
Half the pitch plus clearance; 0.060 in total for 10 TPI general purpose.
What is a stub Acme?
A shallower Acme form, about 0.3 × pitch deep.
Can I use a 60° tool?
No; the form must be 29° with a flat tip.
How do I check an Acme thread?
Fit the mating nut or measure pitch diameter with wires.
Related guides and calculators
- How to Cut Threads on a Lathe
- How to Cut Internal Threads on a Lathe
- How to Measure Threads with Three Wires
- How to Set Tool Height on a Lathe
- Thread Gage Basics
- How to Turn Between Centers With a Lathe Dog
- How to Cut Square Threads on a Lathe
- How to Cut Buttress Threads on a Lathe
- How to Cut Internal Acme Threads
- How to Cut Multiple-Start Threads on a Lathe
- All free machinist calculators
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