The Change Gear Calculator

This calculates the change gears needed to cut a given thread on lathes that use up to 6 change gears. It works for both metric and inch based lead screws, and threads to be cut.

Note that some solutions listed may not actually fit on a given lathe, so you'll have to verify final fit.

Options (Table of solutions automatically updates on any change.)
Leadscrew:	mm Pitch TPI
Thread to Cut:	mm Pitch TPI
Sample Gear Sets:
Available Gears:	Enter a comma seperated list of gears, or select from Sample Gear Sets (above). (Press enter, or exit field, to commit changes.)
Tolerance ²:	% difference between calculated and desired threads.³
Solutions to Show	2-gear 4-gear 6-gear ⁴ Maximum:

Footnotes

1. When gears B & C are "any", there are two possible gear arrangements:

a 2-gear setup, where B is just an idler gear between A & D, and C is just a spacer for B.
a 4-gear setup, where B & C must be the same size, and together just act as an idler between A & D.

2. Tolerance is the max acceptable error ratio between the desired & actual threads for a given gear set. This is needed as some gear combinations, while usable, may not produce mathematically exact ratios for a desired thread. A common example is when cutting an inch based thread (TPI) on a lathe with a metric leadscrew (or vice versa). However, as most nuts only have a few threads, and therefore most screws & nuts only have a few threads of engagement, with a reasonable tolerance, the resultant thread will generally be more than precise enough.

3. The formula for the tolerance % is:
| (calculated thread / desired thread) - 1 | * 100

4. When the 6-gear option is checked, it can take a while to compute a list of solutions. This becomes noticeable when the number of Available Gears is over 12.
And, if you have an old computer, it may take longer, sooner (with fewer Available Gears).

5. Filters: list only the solutions that contain the specified gear for each column.
Only one value may be listed in the filter for each column.