OK, a report on the latest ESS driver for Mach3 and threading.
The background is that with only one speed update per rev, threading anything difficult with Mach3/ESS was often just not possible. If the cutting forces were significant, the spindle would slow down and the thread would be ruined. I had been nagging Andy at Warp9 about PID control for Mach3. When the latest driver was released I tried it but found that the full PID stuff still did not work - although the Proportional part does. This is now acknowledged.
Then I made a throw-way comment on the Warp9 Forum that I don't NEED real PID control; I just need the ESS to sync the Z axis movement with the real Spindle speed much faster than one index pulse per rev. To which Andy replied that this feature had been included in the latest driver. I had just not seen any mention of it.
So, today I went into the bowels of Mach3 and of the ESS driver and configured it all for the 512 line encoder which was already on the lathe spindle. Then I ran some tests.
#1: Soft plastic, M12x1.0 metric fine thread, HSS threading tip. I chose this because I have taps and a die for it for comparison. Result: success - but that was soft plastic which would not slow the spindle down.
#2: Using the general test program I had written for #1, I then cut a thread on 5000-series aluminium. This is harder than plastic, but still not all that much of a load on the spindle. This let me fine tune the tip-correction factor for the tool in use (HSS, 60 degrees, sharp tip). The result was successful when tested against the M12x1 die.
#3: A real test: an M14x1 thread on forged steel. (It was some scrap I had rescued ...) This is where all previous efforts had failed: the steel is very tough and the spindle does slow down at times. The thread used to get trashed. Away we went, and the spindle did slow down in places. Quite apart from the fluctuating RPM on the Mach3 screen, I could SEE the spindle slowing. I swear it must have come close to dropping to 50% of speed at least once. OK, it was not a very conservative cut - but that was the whole idea.
Result: a quite satisfactory thread! No sign of wobbles in the pitch. This was checked against a Moore&Wright thread gauge and an M14x1 die I have. Just lovely, despite the variations in RPM.
Conclusion: the dynamic syncing between spindle RPM and Z-axis movement in the latest ESS driver works fine with a good-enough encoder (512 lines is the top end of what is available cheaply). I would imagine that a 256 line encoder would also work OK, or even a 128 line one. I don't care if the actual RPM is different from what was programmed, as long as the threading works on steel! Which it now does.
Thank you Andy.
Cheers
Roger