printing shifting problem

[thixio1 0]

After a certain height, the printer shifts the layers, the short belt in the rear gets loose. What can I do?

[macua85 52]

If the short belts are coming loose, its probably due to the motor not being tight enough. Is it a UMO or UM2? on a UMO its easy to fix...just lose motor screws, press down on motor until desired belt tension is reached, then retighten the screws. I imagine its the same procedure on the UM2, but may have to remove the motor shields.

Also check your pulleys are tight while you are at it. There is a small grub screw in them which you can tighten with the appropriately sized hex key.

[gr5 2,071]

This doesn't sound like a belt tightening issue - but a pulley tightening issue. Tighten the hell out of the tiny screw inside the pulleys - so tight that the tool twists a little. There are 6 pulleys on each axis (not 4!). the most important pulleys are the 2 on the short belt.

[thixio1 0]

I reduced the acceleration from 4000 to 1100 and it works just fine again. Either a pulley or a motor overheating problem.

[gr5 2,071]

Tighten the pulleys - takes 5 minutes.

Edited September 18, 2015 by Guest

[gr5 2,071]

Lower acceleration will wreck the quality of the Ultimaker and you will essentially have a makerbot. Lower acceleration means you have the head and therefore the extruder slowing down at every corner. The feeder doesn't like to slow down and speed up - there is quite a pressure build up in the bowden and in the head and slowing down will therefore cause the printer to overextrude for a split second and then accelerating out of the corner you will get underextrusion for a split second. This gives you knobby corners and other lower quality.

[thixio1 0]

Tightened the pulleys, but they all were tight already. Printing with normal acceleration and 50% speed works good. Now checking normal speed again.

[gr5 2,071]

Tightened the pulleys, but they all were tight already. Printing with normal acceleration and 50% speed works good. Now checking normal speed again.

 

All 6 pulleys per axis?  Most people say they "tightened pulleys" but they only did 4 of them.  It's the other 2 - the ones on the short belt that are the problem 90% of the time.  You want them tight as hell - the tool should twist a bit.

Edited October 6, 2015 by Guest

[thixio1 0]

Thanks for your comment. yeah I also tightened the ones of the short belts.

[macua85 52]

I've just seen what happens to my printer on a layer shift. I happened to be in the room servicing my other printer when the problem started. As suspected, the motor was skipping, so I assumed my theory of the stepper drivers was correct (after i have replaced the motors). However, when I turned the machine off and went to move the print head by hand, it was jammed solid. With a little persuasion, it moved again and all was back to silky smooth movement. When I did direct drive conversion, I used to (i think) h6 rods, which are ever so slightly larger than standard 8mm rods. Thus, the bronze bearings are a tight fit, but move ok still. I think the problem is it goes slightly off square somehow (the head/6mm rods), and jams up. I'm not sure how to fix it yet, may just end up going back to non direct drive.

[gr5 2,071]

I don't think you've even said what printer you have. Can you also supply a picture or 5 second video of the "short belt getting loose"? I'm not sure what you mean.

[macua85 52]

SO my issue is solved I think. As I had assumed, it was slightly off square, being forced so by the twister blocks i'm using and tightening the clamps too tight. All seems fine now. I figured this after I just got new rods and bearings in the post! Oh well, for another project I guess!

Edited October 13, 2015 by Guest