| Pass | Depth this pass (in) | Cumulative depth (in) |
|---|
Why Thread Passes Get Shallower
A single-point threading tool cutting at constant radial depth per pass would face a rapidly growing chip cross-section as the thread gets deeper, since the V-groove widens with depth even while the radial increment stays the same. Spacing pass depths on a square-root curve instead keeps the area of metal removed roughly similar pass to pass, which keeps tool pressure and chip load more consistent from the first roughing pass to the last finishing pass.
Choosing a Pass Count
More passes means lighter cuts and better surface finish and tool life, but also more cycle time, so harder materials and finer pitches generally want more passes while soft materials and coarse threads can often get away with fewer. Six to ten passes is a common range for a typical single-point lathe threading operation.
Using This With Compound Infeed
This calculator gives you the radial depth to remove on each pass, if your lathe's threading setup feeds in along an angled compound slide rather than straight in, run each pass's depth through the Threading Compound Infeed Calculator to convert it into the actual compound dial reading for that pass.