matthew.l7
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Y Axis crash detection and skipping on MK3

Jan 14, 2019 7:45 am

Hi everyone. Over the past several weeks my MK3 has started to skip on the y-axis, it started on a complex print, so I inspected the printer and noticed that the front idler was loose with about a 2 to 3 mm gap between it and the frame. I tighten it up and started printing again and it seemed alright till about 5 days ago. Once another layer shift occurred on the y-axis I did some reading and it seemed like there was some issue and the common advice was to disable crash detection, so for a test I did and it seemed as though the issue might be resolved. It was not, so I started to do some digging and came across a support article that mentioned the belt tension and how to check it after a self test in the menu. I ran self test and everything past, but the y axis was really close to 280 so I tightened it up by a tooth and ran self test again, it then registered 240. However, problem not solved. Today I had 2 small (different prints) shift again. So, I turned on crash detection again and printed the whistle on the sd card. The printer detected 3 crashes while printing the whistle and reentered itself. I have checked for debris, the y-axis does not have any obstruction, the belt is tensioned to spec, the rails are lubricated and everything moves freely, I have checked to make sure everything is tight, including the stepper gear and bracket, idler, frame, a basic once over of the entire printer. But I cannot print a whistle without running into several y-axis crashes. I have also updated firmware to 3.5.1. I am not sure what do at this point. I have a MK2.5 I can use, but it sees more limited use since we received the mk3 about 4 months ago. Oh, I should add I purchased the printer pre-built, but am very familiar with its workings. Any suggestions are much appreciated.

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joan.t
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Re: Y Axis crash detection and skipping on MK3

Jan 14, 2019 8:09 am

when the printer is at rest, does the y axis move smoothly backward and forward?

if not, problems could be
motor pulley rubbing on motor case,
idler pulley mounting bolt over tight causing friction,#
idler bearing failing
cabling snagging
linear bearings needing lubrication
linear bearings failing
or something similar

regards Joan
I try to make suggestions that I believe to be well founded and safe,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions,
what you do, is YOUR responsibility.

matthew.l7
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Re: Y Axis crash detection and skipping on MK3

Jan 15, 2019 4:51 am

Joan, thank you so much for the response. I spent a few hours with chat support last night and made a little progress. We went through some of these things together. while taking some photos to send to support my bed skip a tooth on the retainer. I did a self test and the bet tension came back at 265, it was 240 previously. I tried to print the whistle again and it finished without any y-crashes. However today, we started a larger print and about 20% complete and it skipped again, it did not detect a y-axis crash and kept printing. Last night support suggested unplugging power panic and seeing if that helps. In the process I have done the following:

-make sure all components are tight.
-make sure all components move freely
-the bearing are lubricated and move freely
-make sure the gear scrub screws are tight

The idler seems to move smoothly, however I have not tried it under stress. So that will be next. I am thinking of back revving the firmware, has anyone ever done this?

guy.k2
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Re: Y Axis crash detection and skipping on MK3

Jan 15, 2019 6:40 am

Testing the y-axis is easier if you isolate the components.

Release all tension on the y-belt and detach both ends of it from y-carriage. Remember which end goes into which slot of the belt holder.

Move carriage back and forth. There should be no binding anywhere along y-axis travel. If you detect binding, remove the heatbed to access the bearing mounts.

Slightly loosen the u-bolt nuts and test if that removes binding.

If loosening u-bolts helps, very gradually re-tighten the nuts until snug, but not causing any binding.

If loosening u-bolts helps does not help, suspect bad bearing or bearing needing cleaning/greasing. That means pull the rods and bearings.


----
Idler pulley check.
With y-carriage moved all the way rearward out of the way, manually check how freely the idler pulley moves with the belt.
Do so by holding two ends of belt in your hands and manually run the belt back and forth through idler pulley. You should practically zero friction.
If you detect friction or binding, check pulley mount and/or its bearing.

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