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Author Topic: whats happening with threading  (Read 14234 times)

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Offline RICH

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Re: whats happening with threading
« Reply #10 on: December 03, 2008, 07:38:31 PM »
Hi  ALL,
I haven't tried threading with V3.042.20 or even loaded it on the my laptop.

So just want to peg a time line and version which was used by me and some info for others to relate.
 
The last threading I did was with V3.042.018. Steppers,Single index slot, G32 code ( no G76 CANNED CYCLE )
and all worked just great. Before cutting any threads, spindle speed ( manually set and manually varied)
along with the G94 the G95 was checked. Mach's RPM readout was the best ever, varying and recovering to correct DRO indication inclusive of the z axis behaving appropriately. Backlash compensation was used.

Now i only cut about five threads.
The first experiment confirmed to me that the puny lathe was going to do good because spindle slow down  was varied to mimic a heavy cut  and the z movement responded, tried to deliberately screw the thread up by manipulating the speed at the start, during ( about 40%), and end of the thread. Leaving two finish passes to clean it up. The thread didn't come out to well, but, remember this was just a brutal test.

Now the other ones were "very good" and to dimension. So with that limited testing......life is good.....and left things alone.

The SS stepper setup also seemed to work very well in dry running but without backlash available no actual testing was done.

So until I try out .20, can't say much more.
RICH
« Last Edit: December 03, 2008, 07:41:18 PM by RICH »

Offline RICH

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Re: whats happening with threading
« Reply #11 on: December 03, 2008, 08:06:50 PM »
It's been a two weeks, since fooling with threadiing so don't rmember specifics on the new
PLUGIN CONTROL>Turn Diagnostics. It's actualy a pretty neat tool. ART should give the exact description,
but, it shows that index  pulse triggered  thus out of G94 and into G95 ( threading in effect ) and the variations
on the speed ( there is a limit on just how much the speed can vary ( don't ask / don't remember / and what i knew may not apply). Need to keep your eyes on the screen and motors in view for a good indicatioin of what its
telling you ( especialy if you can..... safely.......fool around ). You can see a few of the same things if you click the
   Diag     ( little tab located in the upper left side of the screen) while threading. Don't screw around too much if your running a slow computer.
RICH

Offline ART

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Re: whats happening with threading
« Reply #12 on: December 03, 2008, 09:22:34 PM »
Hi:

 First thing to check is the Spindle RPM, is it stable in its reading? Secondly, try soem G32 moves, Its not clear from the description if this is a G76 or G32 based program,
be nice to see it run in just G32's to see if its a vb error of somekind or not. Also, Id report that spindle.m1s error to Brian, sounds like that macro file is hosed somehow..

Art
Re: whats happening with threading
« Reply #13 on: December 03, 2008, 09:28:38 PM »
my spindle rpm is stable within 1 rpm.This is using a G76.
I'll go out and try a G32 and see what happens.
Re: whats happening with threading
« Reply #14 on: December 04, 2008, 12:53:12 PM »
Here are some further observations I have made today.

If I use auto speed control (PWM) my speed is unstable 285 to 315 at nominal 300 RPM (varies with feedrate on Z axis)
In this condition I get erratic movement of x axis on almost every pass of the thread and variation in pitch. This is the same on G32 and G76.

If I use manual speed control, the speed is quite stable (298 to 300). In this condition most passes of the thread are correct, but 1 or sometimes 2 passes result in movement of the X axis and or variation in feedrate.

After several more tests I was able to observe that once or twice during the complete thread my spindle DRO speed would jump to 1000 RPM for a second or less, then settle back at 300. When this happened, the following pass would have the problem with movement on the X axis and/or change of feedrate, then continue normally. This also happens in both G32 and G76.

It therefore seems that the problem is speed related. I can understand that with the variation in feedrate, but the strange movement of the X axis was not so apparent.

The OP says he has a very steady spindle speed. I thought I did, but it wasn't until I watched the DRO throughout the entire thread that I noticed the momentary change.

I have played with index debounce, speed averaging and step/direction pulse in motor tuning, cleaned the optical switch on the indexer but these don't appear to affect it. I tried reducing the acceleration of the Z axis and this appears to have helped. It may just be a fluke, but I will try some more tests at different levels.

It wasn't my intention to gatecrash the OP's original message, but I believe from todays tests that there is a clear link between the spindle speed feedback and the strange movements on the X axis.
Re: whats happening with threading
« Reply #15 on: December 04, 2008, 01:21:21 PM »
I disagree at the moment on the spindle speed feedback.This problem is only there with treading.
My spindle speed is very stable ,I tried taking very small cuts so no way would the spindle slow down and I get the same
error.I noticed also that when this random x axis takes place it is as if the cycle restarts itself ie,
say 5 cuts fine which should be to finished tread then 5 more cuts tapering in random.
Re: whats happening with threading
« Reply #16 on: December 04, 2008, 01:59:07 PM »
I have just cut 6 successful threads, 3 in G32 and 3 in G76. I solved the momentary blip in spindle speed feedback by switching off enhanced pulsing in general configuration.

I still have the same faults in auto speed, but that is a seperate problem. I will try some more tonight to see if the faults re-occur.

Offline Hood

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Re: whats happening with threading
« Reply #17 on: December 04, 2008, 02:03:41 PM »
Keith, have you monitored the spindle in the plugin to see if it registers a missing index pulse, also whether the rest of the info looks good?
  It may be that you are seeing a very stable speed in the DRO and that you are not taking a deep enough cut to alter it but however it may be the feedback that has a glitch and thus the threading is playing up.
If you look in the Mach3 folder you will see the macro that is for threading (m1076), make a copy to the desktop for backup then open the original from Machs VB Editor and you will see a line that says Test = False (or something like that) Change the False to True and when you get code from the wizard it will produce G32 rather than G76, this will help you see what the wizard is putting out and whether Mach is deviating from it.

Hood
Re: whats happening with threading
« Reply #18 on: December 04, 2008, 03:23:06 PM »
I am now seeing repeatable screwcutting without errors in both G32 and G76.

Offline ART

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Re: whats happening with threading
« Reply #19 on: December 04, 2008, 03:26:21 PM »
Hi:

  Cant see "enhanced pulsing " doing that..
You may want to turn it back on just to be sure, enhanced pulsing usually makes the pulsing
smoother..

Art