PMDX424 - Lathe threading - Mach4

[Tripp]

Hi folks,
I've read all I could find regarding your threading/sync methods.
Can you tell me how you handle the pullout of the tool at the end of the thread ?
Does the Z maintain the constant feed rate during the retraction ?
Thanks,
Tripp

[12strings]

As best I can understand, and looking at the Mach4 Lathe GCode Programming manual (in the Mach4Hobby\Docs directory), page 21 and the example GCode on page 22, the actual threading operation (G32) just cuts the thread.  The "pull out" is, in the example, the "G0 X0.3" and "Z0.1" lines after the G32.  When the G32 move is taking place, the device (SmartBOB in this case) slaves the Z axis speed (i.e. feed rate) and any X axis motion to the actual measured spindle speed.  When the G32 motion ends, that slaving also ends.  The "pull-out" is a normal linear move, or whatever GCode you give it.  The example code's "G0 x0.3 Z0.1" should cut a tapered thread because the spindle is still moving, but this motion will not be synchronized to the actual spindle speed, so it won't exactly match the pitch of the G32-cut thread.

[Tripp]

Also look at G76 on pages 30 thru 35.
I only have the demo MACH4 so I can't display the code that the wizard produces.
I would it is to the Fanuc G76 convention, but its also dependent on the motion control. Nothing, that I know of, could handle the pullout properly in Mach3. I'm wondering if the PMDX can do this correctly with MACH4.

Thanks 12strings,
Russ

[12strings]

Looking at the G76 description, the pull out ("lead out" in the Mach4 doc) is part of the G76 and therefore that motion is controlled by the Mach4 motion planner, same as the rest of the thread cut.  I would *guess* that, yes, the feed rate as specified by the Mach4 motion planner would remain constant for the entire thread cut including the pull/lead out.  The feed rate would be modified by the SmartBOB based on the actual measured spindle speed, even during the pull/lead out section.  So the resulting thread should have a uniform pitch all the way through the pull/lead out.

[Tripp]

Yes, I understand that it "should", I'm looking for evidence that it actually "does".

Thanks 12'

Russ

[12strings]

Yes, I understand that it "should", I'm looking for evidence that it actually "does".

There is an expression is sports training that goes something like this: The best predictor of performance is performance itself.

Run a G67 threading operation, and evidence you shall have.

[Tripp]

Thanks, but i only have the demo ... no code posted. And, I dont yet have a PMDX controller ... which is where the code is executed.  No way to see it ... yet.
Thanks again.

[spencyg]

FYI, I just setup my lathe with a 424 board with a 407 piggyback for the spindle. My initial impressions are pretty good and it does thread very nicely with the single pulse per rev signal I'm inputting into the board. There is an issue with shutting off the spindle after the G32 (threading) moves are complete but I've been told they are working on that. I was previously threading with an ESS on Mach3 and the threads being cut by the 424 and Mach4 are significantly cleaner. As with all G32 routines, the lathe cuts the thread at the designated inch per revolution and then retracts first in the X, then in the Z with a rapid move.

[Tripp]

This is good information, thank you for reporting your findings.
Regards.

[spencyg]

I hate to bring this thread back, but was threading ever corrected for the 424 board? It is probably obvious that I don't use the lathe much and only now have a new job that has come up where threading is required. The previous issues of the spindle not shutting down and the program stalling still exist, though admittedly I haven't done anything to fix it in a few years since I was told it was a firmware problem on the board itself. Has the 424 threading issues been ironed out over the last 36-40 months?

Please advise.