Update from older software version

[LeChuck]

When I calibrated the revs ratio, the machine was repeating position back and forth to the zero on the indicator. What I didn't do is run an autotune. The spindle encoder seems to be repeating position exactly. I'll spend more time and see what I can figure out.

[martyscncgarage]

Yes, run the DMMDRV Autotune.

[tblough]

When you calibrated, what speed were you moving at? The threading cycle (and other Intercon cycles) use rapid moves which require more power. If your motor/drives cannot provide that extra power, then they will drop steps and loose position.

As Dana and Marty have already stated, you are loosing position. For threading, that is either loosing steps on Z because of stalling or noise, or rotational position on the spindle because of noise or encoder problems and the spindle is not repeating on the index pulse.

Since the threading cycle you posted has you threading with T3 to Z-6.5, put tool #3 in the tool holder and manually move the z-axis to, say, -10. Set up a dial indicator and zero it on the tool at that position. Now run your threading cycle. After the threading cycle finishes, manually move your tool back to Z-10. Is the dial indicator still at 0? If not, then you are loosing steps in Z. If it is at -10, the we need to look at the index pulse from your spindle encoder.

[LeChuck]

Alright, I'll test that. Regarding the autotune, no luck so far. My servo model isn't in the DMMDRV selection list and it won't let me use the correct custom values (doesn't accept a decimal). Looks like I'm going to be going from one issue to the next with this. Ugh.

[LeChuck]

Losing steps, isn't it a stepper motor thing normally?

[tblough]

It IS a stepper thing, but the Acorn IS an open-loop stepper controller. Even if you are using closed-loop servo drives with an Acorn, the Acorn is still open-loop and the only way it knows there is a problem is if the drives report it AND you have correctly configured the drive fault signals to the Acorn. The Acorn will plow along happily even if the drives are completely stalled if an error condition is not reported.

[LeChuck]

OK, thanks for the explanation regarding open loop. Makes sense. Also, I did crash it earlier, and it went right to drive fault as soon as that happened and stopped everything.

So, I did a few more tests. I won't have time to do anything more scientific before tonight, but I tried a few things and it doesn't look like I'm losing position on Z, at least not enough to explain the mangled thread.

I chucked a piece of material and zeroed Z to it with the main cutter using a piece of paper. I jogged back and forth rapidly for a while using the pendant at 100x, over 2 or 3 inches, more times than any movement in my program. I went back to zero and the paper fit the same way.

Then I ran the job, and interrupted it before the final cutoff cycle. I went back to tool one after it went back toward home, and jogged to -0.5 (because there's a 0.5mm facing operation at the beginning so the face is now at -0.5), and as you see on the photo, the cutter is right on the piece.

I ran it one more time and let the whole program cut air then do the parting (it's straight now), then I went to tool 3 (threading) and jogged it to -17mm (parting position), and as you can see in the next photo, it's right on as well. My photo angle was a bit off.

So I won't be able to do more tests right now, but there's one thing I want to try first, selecting an existing thread from the database, like 1.25 or 1.5, and see if that one works, for a hunch.

[LeChuck]

Well, it wasn't that. But I ran it 2 times again without resetting any positions in between, and the threading point is in the correct exact spot at -17mm at the end of the second job.

[LeChuck]

This is odd though: the spindle encoder has been set to -8000 since this lathe arrived (why negative?) but I'm counting 10000 ticks per revolution in my manual test. Shouldn't these numbers be the same? This might actually explain why it looks like it's making a 1.25 pitch instead of an 1.0 and also losing sync.

[tblough]

Negative means that the encoder counts backwards from the spindle rotation. Instead of counting ticks and guessing, post a photo of the label on the encoder so we can see exactly how many LPR it has. Having the spindle PPR incorrect will definitely cause what you are seeing.