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« on: June 24, 2018, 02:53:33 AM »
It is more accurate to say that Mach3 synchronises the feed to the spindle. Given that you replaced the h/s servo motor with a 1.5 hp induction motor I don't think you will see much variation of speed with lightish cuts. My Super 7 has half that power in a single phase induction motor and I don't get any threading problems due to the spindle slowing down.
As Joe indicates, Mach3 uses the spindle index pulse both to measure the spindle RPM, which it uses to calculate the Z feed rate for the pitch you want; and also to synchronize the Z feed, starting it at the same relative position for each pass. To a limited extent I think it can adapt to small changes in speed caused by cutting force, but with only one sample per rev it can't do a wonderful job.
I think one can obsess about Mach3 threading - given a reasonable amount of motor power and if you don't take aggressive cuts, it WORKS.