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Print skipping/shifting at high layers

Posted by wumbo6 
Print skipping/shifting at high layers
January 07, 2014 06:26AM
Hey guys. I have been working on getting my prusa i3 to print more consistently. It has been going fairly well with small prints, however today while printing an extra x-carriage I ran into this issue. The print seems to be shifting/skipping at high layer heights when it is almost done. I adjusted the driver pots so the vref is about 25% higher than the voltage it needs to move(approx .2v for axis and .5v for extruder). This happened twice around the same area where it skips a little in the y direction then more and more every few layers. The second one skipped a few layers higher than the first. I was away from my desk the first print but was there when it happened the second time. I had been checking the temperature of the drivers pretty constantly and were barely warm for the entire duration of the print. I have them heat sinked as well as a 120mm fan about 3" from the board. On top of that, for the second print I placed a really big house fan blowing at the electronics and steppers. I am seriously stumped as to why this is happening. My speeds in marlin are all set to their default values and was an estimated 5 hour print
Anybody have any ideas?


Edited 2 time(s). Last edit at 01/07/2014 06:28AM by wumbo6.
Re: Print skipping/shifting at high layers
January 07, 2014 06:49AM
Z step not correct? (would expect issues lower down)
Or extruding slightly to much so that it build up and eventually knocks your Hotend ? (cant see any drag marks)
Or the axis it is skipping on needs a little more current. I'm guessing its on the Y axis that skips.. It could just be a weight thing... pololu current set a fraction to low and as weight build up it cant move the mass anymore.

I suspect its the last one.
Re: Print skipping/shifting at high layers
January 07, 2014 07:54PM
Thanks for the response! The bed is pretty hard to stall with my hand when it is moving. I will give it a try anyways. As for over extrusion, I am using 3mm filament and using a multiplier of 95%. Any other possibilities?
Re: Print skipping/shifting at high layers
January 07, 2014 11:10PM
Thanks for the response!
Re: Print skipping/shifting at high layers
January 08, 2014 12:44AM
that's what exactly happened to me with my x axis mendel. I just realist this problem occurs while printing the tall parts. 5 hour spending time in from of pc and read some people posting still unsure what is the real problem caused this.
might be a marlin / firmware incorrect setting / value, or the malfunction of the hardware can caused this.
I have tried many kind of solution listed, trim a pot, check the belt / pulley, etc

but last night I tried to edit my config.h and lowering the max acceleration down to 2000 (originally 9000) the result is terrible, at low speed of printing (specially on the 1st layer) the skipping is just occur every print in x axis, so I revert back to 8000 (lowering bit down from original marlin value), will try the result tonight since now i am at work.
Re: Print skipping/shifting at high layers
January 08, 2014 12:16PM
I would check your stepper drives are properly adjusted AND are properly being cooled.

-Too low current setting and the drives will skip
-depending on what drives your using, No cooling or too high current setting causes the drive to get hot and go into protection mode(turn off the drive) until it cools down then it resumes working.

I would switch to repetier FW, I found it's much better and less bugs.
Re: Print skipping/shifting at high layers
January 08, 2014 09:54PM
I had a ton of cooling on it. All my steppers had heatsinks on them, I had a 120mm fan blowing on the boards a few inches away as well as a regular sized house fan on max for the entire duration of the print. I was also printing from SD so i'm assuming I can rule out the computer not sending commands quick enough. I guess a possibility is that the heat is not conducting well enough to the heat sink. I noticed my extruder was skipping and felt the heat sink and it was barely warm.
Re: Print skipping/shifting at high layers
January 08, 2014 11:10PM
Are you running any Z-lift on retraction/travel moves? I was recently having this very same problem with inconsistant filament. When I have better filament and am really dialed in on my extrusion, I don't normally use any Z-lift at all.

I just use a value that is double my layer height and it very much solved this for me.

I run 5 day prints, really sucks when something like that happens at 4 1/2 days.!

Once your print drops that first step, the next several layers cause even more lost steps.

Hopefully you are not loosing Z steps. I run a little gcode test before longer prints that just moves my Z-axis form 10mm to 200mm about 20 times to make sure that there is no binding or lost steps. I don't run from 0mm because I don't run limit switches and I don't want to crash into the bed if steps are lost when moving up and going to far when coming down.

Edited 3 time(s). Last edit at 01/08/2014 11:20PM by Dirty Steve.
Re: Print skipping/shifting at high layers
January 09, 2014 07:35PM
I dont use any z retraction during my prints. It may be more general of a problem than I had first thought. My prints are now skipping in the x&y axis at much lower heights now. I have upped the pots on both drivers and am printing something to test it out. Does anybody know if drivers have been known to go bad over time? These are genuine pololus but have only installed these heat sinks this week after running them for about 6 months without.
Re: Print skipping/shifting at high layers
January 18, 2014 09:21PM
Mostly posting here so I can find it easy later but I am having the same problem that happens on later 53 or 54 of my 59 layer print after running the same print multiple times (talking about 20 times). I made sure to watch for it and right now the only thing I can think of is a loose belt because there aren't really any noises etc, the hotend just misses the print. I'm actively looking for a solution though and will report back.
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