z axis randomly plunges too deep

banana
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z axis randomly plunges too deep

Post by banana » Sun Apr 27, 2014 3:56 pm

I finished my shapeoko 2 assembly(full kit from invebtables) a few weeks ago and still haven't got it working. It may cut fine for a minute or for an hour and then it ruins everything by having the z axis go down further than it should, usually by 1-5 mm. The universal gcode visualization shows the paths as they should be so it doesn't look like there's a problem with that. The z axis itself was a pain to set up but it seems to run by now, it moves smooth and even either turned by hand from the couple or jogged up and down from the universalgcodesender.

I am currently trying out meshcam and I set the Z plunge rate down to 50mmpm and it still randomly overplunges.

Any ideas?

My grbl settings are the same as suggested on docs.shapeoko.com, here's the file I'm trying to cut http://www.speedyshare.com/agjWG/mc-rauh.nc

twforeman
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Re: z axis randomly plunges too deep

Post by twforeman » Sun Apr 27, 2014 4:07 pm

Check for the following:

Loose wires.
Loose motor coupling.
Do you have a fan cooling the controller board?
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banana
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Joined: Sun Apr 27, 2014 2:07 pm

Re: z axis randomly plunges too deep

Post by banana » Sun Apr 27, 2014 4:25 pm

Thanks for the advice!

I've gone through all the bolts and nuts to make sure they're not loose.

I don't have any cooling, the ambient temperature is.. well chilly enough to have to wear a sweater. The controller board doesn't have a case, I was supposed to build one but haven't gotten around to it as the whole thing isn't even working yet.

Will check the wiring.

twforeman
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Re: z axis randomly plunges too deep

Post by twforeman » Sun Apr 27, 2014 4:35 pm

You really need a fan blowing on the controller board, even if it's cold where you are running it.

Ambient air will not do it, and overheating drivers will go into thermal shutdown.
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banana
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Re: z axis randomly plunges too deep

Post by banana » Sun Apr 27, 2014 4:53 pm

That's odd, I bought a full kit expecting a full kit. No fan in the box and I didn't see any cooling necessities mentioned in the assembly instructions.

WillAdams
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Re: z axis randomly plunges too deep

Post by WillAdams » Sun Apr 27, 2014 5:22 pm

Before adding active cooling you should adjust your current:

http://www.shapeoko.com/wiki/index.php/ ... or_Current

Active cooling was essential for the green stepper drivers typically used on the SO1 --- for the SO2 w/ black stepper drivers which handle temperature better, active cooling becomes an option, albeit one which many choose, and which will probably help your electronics to last longer.
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banana
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Re: z axis randomly plunges too deep

Post by banana » Sun Apr 27, 2014 7:02 pm

It says that too high current may lead to drivers overheating and shutting down- would it be possible that once the driver shuts down the motor keeps going and plunges the z axis too far? If the drivers overheat and shut down would they instantly come back on and pick up where they left off?

*I have no idea what I'm talking about

WillAdams
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Re: z axis randomly plunges too deep

Post by WillAdams » Sun Apr 27, 2014 7:16 pm

Possibly it's not electrical though --- the 1--1.5mm too deep you mentioned sounds like the machine is deflecting that amount for some reason.

http://www.shapeoko.com/wiki/index.php/ ... m_Expected
Z-axis cuts more deeply than expected: The bit is pulled along going deeper into the material than it should.

Spindle is loose in its mounts, Z-axis plunge rate too fast causing the machine to go deeper than it ought.

Always check to ensure the spindle is secure. Always be cautious with Z-axis plunge rates, especially when using CAM tools which lack spiral or ramp Z-axis moves.
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banana
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Re: z axis randomly plunges too deep

Post by banana » Sun Apr 27, 2014 7:52 pm

1-5, not 1-1.5

I've gone over all that could be too loose or too tight. When it plunges too deep it does it smoothly, like it was supposed to and then continues to cut the pattern fine, just on a wrong level. For example when milling a planar level it does the first half fine, then the bit lifts up and goes to do the second half that should be the same level but once it starts it plunges too far down.

On the attached picture it was leveling fine (green highlight) until it was not (red highlight), the green highlighted plain was supposed to be twice as large but I cancelled the milling when I saw it plunge too far down. Bit was 3.2mm ball end, overlap 2mm, the coin is a quarter. Path file in OP.
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cvoinescu
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Re: z axis randomly plunges too deep

Post by cvoinescu » Sun Apr 27, 2014 8:49 pm

Let me put it this way: your Z axis does not over-plunge, it under-retracts. Which amounts to the same thing -- Z axis too low -- but it also explains how missed steps, or a driver going in thermal overload, could cause it to go further than intended (because, as you mentioned, it's a bit counter-intuitive that the motor failing to run could cause it to go further).
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