Hey Bob,
This from your first post:
I currently have an opto-coupled feedback sensor that appears to give me stable RPM numbers.
What type of sensor is this ? Later you mention reflective target or such.
Is it sensing on the actual spindle and not the motor or other shaft ?
I for some reason suspect the index signal to Mach to be the problem.
And did you follow Hood's suggestion ?
Have you enabled the turn diagnostics plugin and then monitored to see if there are any problems with your index pulse?
Hood
Threading is working flawlessly here. Actuall threaded 900 pieces today and yesterday, 48 TPI. My best run yet.
The spindle sensor shines an IR LED at the spindle shaft and uses a phototransistor to sense it. The shiny shaft is interrupted by a piece of black tape.
The design is from Dave Hyland's website,
http://davehylands.com/Machinist/CNC/CNC-Spindle-Encoder/index.html#01-Encoder.jpg and I know Dave has successfully used it. I have had one screw of many turn out acceptably.
As I told Hood, I did not spend enough time trying to use that tool but tried a couple of times and didn't see how to get info out of it.
I am also suspecting my feedback pulse, although I want to go check that the settings that Rich pointed out are correct.
Here's where I think I am:
1) I think I've ruled out the Z-axis stepper loosing steps. I've run repetitive back and forth motions (20 round trips one time) cutting a rod down and the lathe returns to the same point every time. I've done this a couple of times and different ways. The cut pieces are the right shape without stairsteps from being cut in the wrong place.
2) Since I'm running the spindle at full speed while I'm doing this, I think that rules out EMI from the motor into the Xylotex controller. I had that problem on my mill, although it took hundreds of back and forth moves to really show up.
3) I think I've ruled out the Z axis motor being too wimpy by doing everything at slow speed. The Sherline motor should have around 450 in-oz of torque at the low speeds I'm running. My Z axis is running at 50% of top speed, or less.
4) I've actually watched the threading progress under a 10X magnifier, and I see the cutter not following the thread. It's like it's starting out of sync by some "phase error" (30 degrees, 60...90... it varies). It could be starting in the wrong place in Z, but I think I trust the Z axis (as I said in (1) ).
I think what might be happening is that the spindle pulse doesn't "look" right to the interface. I think it's possible that the spindle sensor might be putting out false or extra edges - perhaps caused by EMI to the sensor from the stepper motors, or the Sherline motor. That is what I wanted to try and test tonight.
Bob