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Author Topic: Mach lathe losing position  (Read 6452 times)

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Mach lathe losing position
« on: March 13, 2012, 02:37:12 PM »
Hello all,

Starting to get my lathe alive and running parts, and having an issue. I seem to be losing position occasionally. I played with the PID settings on the Granite servo drive, and got my following error limit down to 15 counts (20,000 per inch), so I think that should run pretty tight. So I'm trying to run multiple pieces. I'm using 5 tools: face/turn, center drill, drill, cutoff, and barpull. The facing and turning seems to go fine, but occasionally the shoulder I'm turning comes up .005-.010" too long or too short. The bigger problem is when cutting off the part, it can be .05-.100" too long or short. As if Mach is losing position during the tool changes or rapid moves. This doesn't happen every time. The shoulder is off in 1 part in about 10, and the overall length has been of maybe 1 part in 5.

I've tried rehoming the Z axsis, and it generally ends up way off (.100-.200) after doing so.

So where am I losing counts? I guess I need help understanding the failure modes that are possible.

Thanks for reading!

Kevin

Offline Hood

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Re: Mach lathe losing position
« Reply #1 on: March 19, 2012, 08:13:34 AM »
Could be the active state or you step pulse is wrong or even the pulse width is needing widened.
If using electronic gearing in the Granites that may be the issue, no experience with the Granites but I do know other non industrial drives that have electronic gearing can have issues with it.

Hood
Re: Mach lathe losing position
« Reply #2 on: March 19, 2012, 01:58:20 PM »
Thanks for the reply Hood.

No electronic gearing in use. I increased the step pulse width to "5," and lowered the output frequency in the smoothstepper config from 1Mhz to 512khz. Seems to be working better than it was.

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Re: Mach lathe losing position
« Reply #3 on: March 19, 2012, 02:21:16 PM »
Oh sorry pulse wdth will have no affect if using the SS.

Hood
Re: Mach lathe losing position
« Reply #4 on: March 19, 2012, 02:36:31 PM »
What effect does the pulse frequency in SS config have?

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Re: Mach lathe losing position
« Reply #5 on: March 19, 2012, 02:40:16 PM »
If you are meaning the controller frequency then it should have no affect on the issue you are having. Where it would have an affect is if you  were running out of data being sent to the SS, ie getting that message and hangups etc.
Hood
Re: Mach lathe losing position
« Reply #6 on: March 19, 2012, 03:10:54 PM »
No, it was the maximum output frequency that I was looking at. The instructions say if it is say to high, you lose some resolution.

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Re: Mach lathe losing position
« Reply #7 on: March 19, 2012, 03:19:27 PM »
Are you meaning the frequency for each axis? If so set that to what you need or the next nearest above. If you go higher than you need then you will be using overheads that you do not require but you should not lose any resolution
Where it may become a problem is the pulse width may become to small for your drives if you have it set too high.
Hood
Re: Mach lathe losing position
« Reply #8 on: March 19, 2012, 03:23:08 PM »
How do I know what I need?

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Re: Mach lathe losing position
« Reply #9 on: March 19, 2012, 03:24:52 PM »
what is your steps per unit and velocity?
Hood