Lathe spindle speed/index from working mach3....

pbreed wrote:

My lathe spindle has an optical interrupter wheel with one slot twice as wide as all the others.

When you say "twice as wide" do you mean "twice as long"?
How many optical detectors are in the system?

It is common to have several slots detected by one sensor and then one long slot that reaches far enough to trigger a second sensor.
But, in theory, it would be possible to detect a missing or longer pulse to provide index. Automotive crank position sensors often use a missing-pulse indexing scheme.

That's interesting. ad you say that Mach3 worked with that?

My impression is that Mach3 only uses one pulse per rev, so perhaps only the long pulse was being passed to Mach3? Can you see every pulse in Halscope?

Is it possible that the original Mach intallation was using something like a Smoothstepper, and that that can handle an missing-pulse index? I have just done a bit of web-searching and have found no evidence that native mach3 can handle a multi-pulse encoder.

The simple answer would be to make a new encoder disc with a conventional index. The elegant and future-useful answer would be to add missing-tooth index to the LinuxCNC encoder counter. Were you looking for a software project, or were you wanting to make the lathe work