Ontopic The 3D printing thread

Jehannum

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That shouldn't kill the Z motor.

Is the motor running hot or anything?
It gets pretty hot, and the failure seems to happen hot.

It hangs in place for a little bit, and makes a grinding/humming noise like the gantry should be going up, then it starts to knock the print with the nozzle.
 
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gee

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Grab a DMM and measure the voltage on the face of the VREF pots. Thing might not have been adjusted right from the factory and it's cooking the Z motor.
 
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gee

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oh shit.

How do I adjust it if that's the case? Do I need a screwdriver that's non-conductive?
Conductive screwdriver is fine provided it's got a plastic handle, or you use a small plastic bag or whatever over a metal screwdriver handle so you don't short the pot to your body.
 
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Jehannum

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Conductive screwdriver is fine provided it's got a plastic handle, or you use a small plastic bag or whatever over a metal screwdriver handle so you don't short the pot to your body.
Should I measure the voltage of the X or Y VREF pots, or is there a specific voltage that I should be looking for?
 

gee

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I'd measure all four pots - X, Y, Z and E.

Not sure what typical voltages are, depends on the current sense resistors, there's probably some good typical values to be found online.
 

Jehannum

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According to github:
Code:
A4988 Drivers
Vref set to ~90% of stepper rated current
Rs = 0.1ohm

X = 0,58v (0,725A)
Y = 0,58v (0,725A)
Z = 0,58v (0,725A)
E = 0,72v (0,900A)
So I just need to check the voltage? I'm not sure how I would measure the amperage.
 

gee

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Just measure the voltage, yeah.

Z doesn't need to be set as high because it's not accelerating things fast and has 4x the mechanical advantage with the leadscrew, dial it back to 0.50V if it's running hot.
 

Jehannum

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Just measure the voltage, yeah.

Z doesn't need to be set as high because it's not accelerating things fast and has 4x the mechanical advantage with the leadscrew, dial it back to 0.50V if it's running hot.
I adjusted it down to .5V. All of the Vrefs were pretty on the money. I also turned the Z rod over, in case there was some schmutz binding it up. It's printing now, we'll see what happens. Since I can't print on glass on account of the new one is in the mail, not on the machine, I'm printing on blue painters tape, 'cuz I don't want to tear chunks out of the buildtac.

This morning before I got back to change the Vref, I swapped the Z and Y stepper motors. The print made it farther, but still ended up making spaghetti with a huge layer shift.
 

Jehannum

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Heh. It's always the simple things...

I tightened the one mount bolt I could get to without dismounting the hot end, and then found out that the other one was loose too. Now I'm ~8h into an 11h print, and it isn't making spaghetti (yet). I think it was head crashing and then either the belt would skip on the X gantry (layer shift), or the bed would come totally off (broken glass).

Time to figure out a fastener locking scheme.