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Author Topic: Intermittent inaccuracy  (Read 3831 times)

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Intermittent inaccuracy
« on: August 15, 2017, 10:01:07 AM »
I noticed my X axis was inaccurate. Went to Settings and re-calibrated X axis. Tested a few times and each time it was spot on. Ran a file that I had cut previously and the X was out again? The problem is intermittent, sometimes accurate, sometimes not. The problem appears to be during the Jog cycle, when the steppers make a sudden noise and stutter. Today I was trying to cut a 2mm deep pocket after cutting about 80% the Z axis started cutting down to almost 6mm. I'm on a steep learning curve so any help or suggestions will be greatly appreciated

Offline Tweakie.CNC

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Re: Intermittent inaccuracy
« Reply #1 on: August 15, 2017, 11:13:31 AM »
Quote
The problem appears to be during the Jog cycle, when the steppers make a sudden noise and stutter.

That sounds like you have one or more stepper motors stalling.

Try reducing your Velocity and Acceleration settings by 50% in Motor Tuning (save the changes for each axis) and see if this cures the problem. If it does then experiment to find the fastest, reliable speeds that suit your machine.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Intermittent inaccuracy
« Reply #2 on: August 28, 2017, 05:33:29 AM »
Hi Tweakie

Thanks for your guidance and sorry for the late response, I have been on leave. I reduced the V & A and so far so good. Perhaps you could help with another issue. The Z axis runs out while cutting a file. 99% of the time it maintains the correct depth, but every so often it gradually cuts deeper, especially when pocketing. Can you help?
Many thanks
Dougie

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Re: Intermittent inaccuracy
« Reply #3 on: August 28, 2017, 05:43:15 AM »
Hi Dougie,

Two possibilities come to mind...

1) Tool slipping / not tight in collet or loose coupling / grub screw, etc. driving the Z axis.
2) Loosing steps when Z axis is raising against gravity - check for mechanical tightness / binding (and that the axis is lubricated correctly) also try reducing the V and A in Motor Tuning.

Is your Z axis stepper motor getting 'hot to the touch' in use ?

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Intermittent inaccuracy
« Reply #4 on: January 24, 2018, 01:20:47 PM »
My Z axis has a gas spring counterbalance because it is heavy and ball screws back drive so well that it comes right down if I hit E-stop or loose power.  This also means the stepper motor doesn't have to overcome the weight of the Z and the load of cutting, so it never misses steps.