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Prints randomly skew x or y

Posted by Chowderhead 
Prints randomly skew x or y
March 07, 2012 09:54PM
Prusa, RAMPS 1.4 on a 2650 r3, Marlin, Slic3r 0.7.0, Pronterface, Windows.

I get one very nice print (in this case a footed vertex) and after clearing the build platform, try to print another with the same gcode and after 4-5 layers the whole print skews 10mm or so towards the x-axis end stop.


Every time (and I've tried at least a dozen times) I try to print an extruder, at some point the printer forgets where it's been and skews the print either x or y, sometimes right after first layer perimeters/start infilling. It seems like the more complex the part, the more likely or promptly the printer starts skewing the print. I've had mixed results with gears -some perfect, some hosed.

What I've done:

Swapped Pololu shields (I have an extra)
Swapped RAMPS (got a friend's)
Swapped Arduinos (got a friend's)
Tried different host computers
Slowed communication between host/printer to 115k
Rerouted conductors so motor leads and hot end leads aren't near each other
Calibrated per the calibration page (motor controllers/extruder/buildplatform/etc.)
Regenerated/rechecked gcode

I have not swapped motors, yet, but that's next. One motor (extruder) is unipolar, the rest are bipolar, could this cause a problem?

Any help is most appreciated.
Re: Prints randomly skew x or y
March 07, 2012 10:21PM
Lower your "default acceleration" in Marlin. I had the same issue...mine mainly was on short repeated moves causing skips.

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Re: Prints randomly skew x or y
March 07, 2012 10:22PM
Lower the initial speed and acceleration in your firmware. Also clean and oil your bars.
Re: Prints randomly skew x or y
March 08, 2012 08:20AM
Thanks! I'll give that shot tonight after work...
Re: Prints randomly skew x or y
March 08, 2012 07:34PM
Do you have a fan blowing on your Pololus? Do you have heat sinks on them as well? Overheating of the drivers will sometimes cause skipping. This is the thermal protection that is built in to the boards.

The acceleration setting is more likely, if you have adequate cooling.
Re: Prints randomly skew x or y
March 08, 2012 09:54PM
What surface are you printing on? If glass are you cleaning it as you need to with something like isopropyl or I use methylated spirits otherwise my prints (PLA) don't stick properly

Experimenting in 3D in New Zealand
Re: Prints randomly skew x or y
March 09, 2012 07:38AM
Well, chalk this up to a violation of the KISS principle.

The issue was the x-axis pulley not being properly assembled (wrong nut) and so the pulley occasionally free wheeled. Doh!

Thanks for all the help and now I'll be starting another thread...
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