9x20 CNC Threading Questions

[Cartierusm]

I've just realized something and hopefully someone can give me an answer.

In a normal manual lathe threading operation the spindle is tied in with the lead screw either by belt or gear. So positioning is not lost by way of the threading dial. On a cnc threading operation the z and spindle are not sync by a physical mean but by a pulse index. So if you stop the lathe to check to make sure a bolt fits on the new threads you just cut won't the positioning be lost? Or is the pulse index used for more than spindle speed timing but for positioning as well?

[Runner4404spd]

position is lost. as far as i know in order to keep the spindle synced you would need an encoder and i don't think mach 3 does that.

[Cartierusm]

I do have an encoder on the spindle. It's the C3 board from CNC4PC. It gives mach a single pulse index that way mach knows the actual spindle speed so it can sync the z axis. Mach must have this in order to do threading on a lathe or a 3 phase motor with a vfd.

[jhowelb]

I have made a practice of stopping Mach 3 to test the fit of a nut and then cutting a bit deeper.

As long as you don't move the slide manually or quit Mach or remove the piece from the chuck then Mach still knows where the slide is relative to the piece and will calculate the angle of the spindle using the pulse.

Try it on a practice piece first!

[Cartierusm]

Thanks I'll do that. I figure that even trying a nut might move it a hair.

[BobWarfield]

Position is not lost with Mach3.

If you have one slot for the index sensor, it knows where that slot is. If you have multiple slots (or reflective markers, Hall effect magnets, or whatever), Mach3 wants one of them to be 50% wider than the others, again so it knows that position.

Cheers,

BW