Z Axis Issue

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Z Axis Issue

Postby Steve T » Wed May 01, 2019 1:56 am

My CNC seems to be working fine with the exception of two times now the Z Axis has got out of control on the start of program and plunged down going through the soft limit and put the tool through the spoil board and into the table.
After which I have removed the tool and tested the program and it worked fine.

Has anyone seen this? or can offer any explanation why this may happen.

Regards,
Steve T
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Re: Z Axis Issue

Postby cncdrive » Wed May 01, 2019 2:00 am

Noise on the step/dir lines probably.
However it would be good to know if the Z coordinates went off position? Or not?
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Re: Z Axis Issue

Postby Steve T » Thu May 02, 2019 12:56 am

The Z coordinate appeared to be reading correct after, i.e. first cut -1.5 mm.
However not sure during the issue as it happens so quick I was hitting the E stop.

If it is noise is this a common issue? and how do I rectify, shielded cable?
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Re: Z Axis Issue

Postby ger21 » Thu May 02, 2019 1:00 am

It could also just be that the Z axis stalled and lost position. This is more likely than noise on the step lines, imo.
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Re: Z Axis Issue

Postby cncdrive » Thu May 02, 2019 1:03 am

If it is a common issue depends on what the problem is.
I don't really know what the issue is in your setup, the information is not enough for me to determinate that.

Bad grounding could possibly corrupt the step/dir signals which go to the drive or it can effect the stepper drives directly causing lost steps.
It is also possible that your motor stalled or jumped out of syncron. Which can be too high acceleration, too high speed, too much resonance or the combination of these.

Shielded cable to where? I did not see your control box, so I don't know where you want to place shielded cables?
If you talking about the USB cable, no, noise can't effect that in a way to cause position errors. Noise on the USB cable could cause communication errors which can only lead to lost and cut connection, because the controller CRC checks all data packets, so it does not execute errorous packets, so it is not possible that noise on the USB cable causing wrong positioning.
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Re: Z Axis Issue

Postby Steve T » Thu May 02, 2019 2:17 am

Re shielding I was referring to the step lines only.
Attached is the Z Axis configuration, could you please check if ok, re the acceleration, speed etc.

Thanks and Regards,
Attachments
Z Axis.jpg
Z Axis configuration
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Re: Z Axis Issue

Postby ger21 » Thu May 02, 2019 10:58 am

Velocity and Acceleration can vary greatly from machine to machine. The only way to set them properly for YOUR machine is with thorough testing.

As a quick test, you can try decreasing the acceleration by 25%-50%, and see if it works better.
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Re: Z Axis Issue

Postby MattTheNoob » Tue May 14, 2019 2:04 am

Did you ever figure out what was going on?
I've smashed my z axis down (usually with brand new expensive cutters) a few times, but it has always been because I didn't set the Z Zero before starting the program.
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Re: Z Axis Issue

Postby 3d0g » Sat Jun 08, 2019 1:25 am

May not be related at all but watch out for Safe Z height in the settings. While UCCNC may not care about imperial or metric, the default value for Safe Z very, very much assumes metric. Crashed Z more times than I care to admit before figuring that one out when I got started.
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