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Author Topic: Threading problem with Mach 3 Turn  (Read 7859 times)

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Threading problem with Mach 3 Turn
« on: December 18, 2008, 06:24:42 AM »
I have just equipped my old Logan lathe with steppers and have successfully gotten pretty good results on the control of the X and Z axes.

I have a Hall effect device (the vane is almost 180 degrees, good long pulse) for the index sensor. It is working fine and the software gives the correct speed.

When I try threading the return passes are way out of sync. with the threads being totally screwed up.

My question: Does Mach 3 need the spindle speed to be EXACTLY the speed specified in the threading wizard or does it continually modify the threading (Z axis) speed to match the spindle speed?

If it is the former then I need to change my motor to one that is WAY more powerful (presently a 1 hp treadmill DC variable speed).

Offline Hood

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Re: Threading problem with Mach 3 Turn
« Reply #1 on: December 18, 2008, 07:34:36 AM »
;ppk at the config menu then Plugins and enable the Turn Diagnostics one. Restart Mach and from the Operator menu open the plugin and then run your thread and see if there is anything amiss. I suspect your pulse may be getting missed but the plugin will say for sure.
Hood
Re: Threading problem with Mach 3 Turn
« Reply #2 on: December 18, 2008, 11:02:56 AM »
Thank you for your response and I will try that (I can't get back to my shop until tomorrow).

To my specific question:  does Mach 3 modify the Z axis feed rate to match a varying spindle speed or does it require the EXACT speed specified in the wizard?

Offline Hood

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Re: Threading problem with Mach 3 Turn
« Reply #3 on: December 18, 2008, 12:02:32 PM »
I am not sure how the parallel port does it now, I think it does but as I run a SmoothStepper I am not sure. With the SmoothStepper it definitely does.
Hood
Re: Threading problem with Mach 3 Turn
« Reply #4 on: December 18, 2008, 04:15:43 PM »
I found that using the printer port the signal for threading is too slow.
I added a dwell at the start of each thread pass g04 p1.This gives the
computer time to sort itself out .I reread your post and it says on the
 return pass,are you not backing the tool out from the cut at the end of the thread?
Re: Threading problem with Mach 3 Turn
« Reply #5 on: December 18, 2008, 05:32:53 PM »
I shouldn't have said "return pass", I meant the second, and subsequent passes don't match each other.  I do have sufficient clearance specified.

I am a real neophyte with G codes, exactly what are you suggesting I do?

Thank you all for your answers on this.

Offline RICH

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Re: Threading problem with Mach 3 Turn
« Reply #6 on: December 18, 2008, 08:02:09 PM »
meincer,
I have the punniest lathe of all, such that the speed will change as the cut gets deeper. Very nice for testing
threading though.....


Mach will vary the Z axis speed dependiing on  what is happening with the spindle speed. It will not allow the Z to increase beyond what the code sets max rpm at. It will slow the Z movement down only to some % of the rpm.
Backlash compensation works fine in threading. If you use one of the wizards it will tell if you are exceeding the motor velocity defined when you did motor tuning, you can then modify rpm accordingly IN THE WIZARD and also set the spindle rpm (manualy in my case). 

You can dry run and watch what is happening in the diagnostics ( barely visible box right under FILE) or the Plug In Control>lathe turn diagnostics. Use it to watch for change of G94 to G95, rpm, etc.

In config>ports & pins> spindle setup / special functions, check "use spindle  feedback in sync mode" and
also spindle speed averaging if your using a slotted disc.

Hope this helps,
RICH


Offline DAlgie

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Re: Threading problem with Mach 3 Turn
« Reply #7 on: December 19, 2008, 10:36:31 PM »
I use the parallel port with my lathe and get perfect results with threading. I, however, do not try to cut threads at 2000 rpm, nor do I set the start point of the thread too close to the part. With a coarse thread and a fast spindle speed the acceleration needed for a lathe with small steppers can easily go under the accelleration rate available, and you end up with a mistimed thread start.
    DaveA.