Whichever it be

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wgollie434
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Whichever it be

Post by wgollie434 » Fri Apr 11, 2014 3:26 pm

I am not quite sure where to post this, so here goes:
I have Shapeopko V2, Audrino Uno, Grbl Shield 3. Sometimes when I am cutting a project
out, the Shapeoko starts to drill to china. That is the bit goes down. For no reason it
does this. It can do it on a job that I have ran before successfully. So this time I did a test
I input code on the command line, using grbl commander, to draw a square, one side at a time. First time around no problem. Gave the
command to lower the bit 2mm for the next 4 sides. Gace the command to cut 100mm on the x-axis. Half way through cutting the x-axis the bit started to go down. Had to do an emergency stop.

I haven't a clue why this is happenening. As I said earlier, it does not do it all the time, just every once in a while.

I use sketchup, phlatboyz, for drawing and code generation. I use ncplot, grbl commander, and gcodesender for talking to the grbl.

cvoinescu
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Re: Whichever it be

Post by cvoinescu » Fri Apr 11, 2014 3:41 pm

Was it just the bit being pulled out the collet, or did the entire Z axis go down?
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

Gadgetman!
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Re: Whichever it be

Post by Gadgetman! » Fri Apr 11, 2014 4:33 pm

Have you tried increasing the current to the motor just a little bit?
(Maybe vibrations are making it move)
Weird guy...
Shapeoko 2014F: 1000mm X/Y, 300W Quiet Cut spindle, Arduino Uno/G-shield and GRBL 0.9i
15x30 drag chains, custom spindle mount, 9mm belts, 8mm endplates, 6mm motor plates.

twforeman
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Re: Whichever it be

Post by twforeman » Fri Apr 11, 2014 5:17 pm

If you don't set the stepper motors to be energized all the time ($7=255) then it's possible the Z axis is drifting down.
Ender 3 3D Printer
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cvoinescu
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Re: Whichever it be

Post by cvoinescu » Fri Apr 11, 2014 6:02 pm

twforeman wrote:If you don't set the stepper motors to be energized all the time ($7=255) then it's possible the Z axis is drifting down.
Not with grblShield/gShield or anything GRBL-based on the Arduino Uno, because all stepper drivers share one enable pin. When X or Y are moving, the Z is necessarily energized too.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

wgollie434
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Re: Whichever it be

Post by wgollie434 » Fri Apr 11, 2014 6:35 pm

The whole Z-axis goes down

cvoinescu
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Re: Whichever it be

Post by cvoinescu » Fri Apr 11, 2014 9:06 pm

Sorry, no idea. But let's think about it. There are several ways this could happen.

It's very hard to backdrive the standard M8 screw -- I'm not saying impossible because, with the right kind of vibration, it may just be possible; but it seems unlikely.

Another way would be for the Z motor to be inadvertently commanded to turn. This could be caused by an electrical problem (a short, but not necessarily), or by a software error. Did you have a chance to notice whether the Z was turning or not as it dove down? If this happened more than once, was it while moving in a particular direction? Could it have been a G-code error, with GRBL simply doing what it was told?

Yet another way would be mechanical failure: a stripped Z leadnut, or the nuts holding the leadscrew getting loose and the screw itself slipping out of the coupler. I assume you examined the Z axis after the event and did not notice a problem, or you would have reported it.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

lordmundi
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Re: Whichever it be

Post by lordmundi » Sat Apr 12, 2014 1:26 pm

or, possibly, is the entire gantry/z axis sliding down? maybe something needs to be tightened there?

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