Threading problem with Mach 3 Turn

[meincer]

I have just equipped my old Logan lathe with steppers and have successfully gotten pretty good results on the control of the X and Z axes.

I have a Hall effect device (the vane is almost 180 degrees, good long pulse) for the index sensor. It is working fine and the software gives the correct speed.

When I try threading the return passes are way out of sync. with the threads being totally screwed up.

My question: Does Mach 3 need the spindle speed to be EXACTLY the speed specified in the threading wizard or does it continually modify the threading (Z axis) speed to match the spindle speed?

If it is the former then I need to change my motor to one that is WAY more powerful (presently a 1 hp treadmill DC variable speed).

[Alan Wright]

Mach3 will use the actual speed of the motor, if the speed is being sensed correctly. I've got a motor which has adequate power for most threading (2 HP), and it holds the spindle speed within a few RPM (I usually thread at 200). However, I have had threads totally screwed up when I was losing a few steps in Z due to heavy cutting forces. I had to tweak the stepper tuning a bit to correct that.

Alan

[jhowelb]

It has been my experience that Mach need to know the exact position (angle) of the spindle.

They specify a certain width of the "window" for an optical sensor in order to set up timing for the pass. Also the ability of the Z axis to accelerate is important, to that end I place the start of the thread about .100" before the actual material to be threaded.

Several years later I find my self still reading and re-reading the Mach manual and groping for answers at times. A bit like witchcraft!! LOL!

Good luck!