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Bizarre threading problem
« on: November 03, 2013, 01:31:51 PM »
OK, it's hair pulling time.

If I use a wizard, any wizard, to thread, the threads come out with the wrong pitch. Not just slightly, but massively. Example, set for 16tpi, it turns out at about 26tpi. Next attempt, it'll be about 24tpi.The threads are consistent in the same run, and track correctly from beginning to end, spindle speed remains constant. These threads would be useable except for the fact that I'd have to make custom nuts for them. Not too many 3/4x26 nuts out there. This has been an ongoing problem. Originally, the threads would get wiped out at the end of the cut during the spring passes. That is, I was threading a 4.5" length and all was ok until the spring passes, at which point the last 2.5" would get wipe off. So upon researching I found that the version I was using was not up to date, 3.040.??? I decided to update to 043.057, but now I can't get past the wrong pitch to even do a spring pass.
 
I have:

-Updated to 3.043.057

-motor tuning and steps set correctly. 1" commanded = 1" move, 4" command = 4" move. It is not losing steps. Returns to correct start point and ends at exact same spot. Like I said, useable thread, just no known standard.

-Set to exact stop

-Backlash is not enabled yet. No need to muddy the waters.

-Diameter mode, tried radius for *********s and giggles

-Debounce to 0. Have tried various other settings. Mach sees the spindle and feeds consistently, just wrong.

-Spindle indexing, feedback, closed loop and averaging set. Indexing/RPM is working correctly. The RPM reads correctly, but the IPR DRO indicates that it is feeding at the bizarre rate for 26TPI. IE, it should read ~.0625 for 16TPI, but it reads ~.02 to .03 . It is like it just pulls an IPR setting out of its ass.

-Tried all infeed methods and angles.

-Tried my origignal xml. It does the same thing, but the spindle response is more accurate. The new xml slowly adjusts to the correct speed, where the old is just there right away. This doesn't seem to affect the threading,a s Mach compensates for the speed difference. Like I said, very consistent thread, beginning to end.

My next thought is to completely uninstall Mach and start fresh. Are there nasty files that don't get replaced when doing an update? If so, how do I kill them off for a totally fresh install?

Anybody have any thoughts?

Please???

Tim

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Re: Bizarre threading problem
« Reply #1 on: November 03, 2013, 01:46:47 PM »
Please attach your xml.
Hood
Re: Bizarre threading problem
« Reply #2 on: November 03, 2013, 01:53:23 PM »
XML attached.

Offline Hood

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Re: Bizarre threading problem
« Reply #3 on: November 03, 2013, 02:01:12 PM »
Turn of the Turn Diagnostic Plugin and restart Mach and see if that helps.
Hood
Re: Bizarre threading problem
« Reply #4 on: November 03, 2013, 02:08:26 PM »
Turned it off. Exactly the same.

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Re: Bizarre threading problem
« Reply #5 on: November 03, 2013, 02:13:23 PM »
Are you using a VFD? Dont see any relays set up in Mach.
Is your ratio correct? you have it at 0.67
Hood
Re: Bizarre threading problem
« Reply #6 on: November 03, 2013, 02:22:31 PM »
I'm using a VFD controlled through mach on a G540, through LPT. Ratio is correct at .67 . I might have to post a pic of the threads. They are really quite lovely! Just useless  :'(

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Re: Bizarre threading problem
« Reply #7 on: November 03, 2013, 02:37:08 PM »
Any way you can confirm the reading in Mach is the same as the spindle, maybe a mechanical tach?
Have you tried with closed loop disabled?
Hood
Re: Bizarre threading problem
« Reply #8 on: November 03, 2013, 02:40:09 PM »
OK, here's an interesting bit: If I change the thread t exactly 2/3's of what I want, they work perfectly. 16TPI, Clean and correct.

What the heck?

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Re: Bizarre threading problem
« Reply #9 on: November 03, 2013, 02:42:26 PM »
seems too much of a coincidence your spindle ratio is set to 2/3 ;)
Hood