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Author Topic: Lathe Threading (Single Point) Fix - Mach 3  (Read 834 times)

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Lathe Threading (Single Point) Fix - Mach 3
« on: May 24, 2019, 09:03:28 PM »
This is an FYI for other users. I hope to help anyone else who has run into this issue.

I was single pointing a screw thread with 28 TPI. The actual thread cut was closer to 29.5 TPI. Perfect looking thread, but just 29.5 TPI.

The fix to this was to uncheck 'Spindle Speed Averaging' under Config>>Ports and Pins>>Spindle Setup. After unchecking/deselecting this option, the thread cut perfectly.

I'm not 100% on why this was happening, but it is interesting that the thread pitch was in error of around 6% and the spindle speed was in error of about 6% (250 rpm command, 267 rpm actual). Is 'Spindle Speed Averaging' somehow causing the system to ignore the actual speed?? Obviously it is still picking up on the index.

My system: Smoothstepper, Mach 3 Version R3.043.062, HF-based CNC lathe

Offline RICH

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Re: Lathe Threading (Single Point) Fix - Mach 3
« Reply #1 on: May 25, 2019, 07:24:49 AM »
You are using a Smoothstepper and the problem would be associated with it, I am thinking.
I don't know what the Smoothstepper is currently doing these days!

Mach3 monitors the spindle speed in real time during the actual threading and if Spindle Speed Averaging
is checked it will modify the NEXT thread path based on the data. One could say it's trying to correct for
a varied / incorrect cut pitch and fix the thread via the feedrate. Idealy your spindle speed should be steady,
the more so the better,but relisticaly it will vary and +- 1 RPM should ok. So if the spindle speed is constant,
spindle speed averaging has little affect on the feedrate.Your spindle speed is what it is and setting of of the
spindle speed should be done manualy, else two systems related to the spindle speed will be fighting each other.
Again, I don't know what the Smoothstepper is currently doing these days!

Control of the threading cycle gets complicated very quickly............