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UM2: low quality prints due to rod displacement

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Posted · UM2: low quality prints due to rod displacement

Hi all,

I have been experiencing low quality prints since I received the ultimaker 2.

Below are the pics which compare the quality between two robots: robot (blue) is printed with my printer and the robot (red) is printed with another ultimaker 2.


2014 04 15 16.55.03

2014 04 15 16.54.39

2014 04 15 16.54.33

2014 04 15 16.54.13


My assumption for the defects is the displacement of rods (both front and rear), which can be seen below.


2014 04 15 16.40.17

2014 04 15 16.40.21

2014 04 15 16.40.31

2014 04 15 16.40.37


The manual movement of extruder in xy axis seems to be quite challenging, especially for x axis, which supports this assumption.

Any advise on possible solutions will be greatly appreciated.




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    Posted · UM2: low quality prints due to rod displacement

    Hi Alican -

    Welcome. I'm sorry to hear you're having some teething problems with your new printer. Are the two prints done using the same gcode file in both cases? I suspect that the print quality differences might be more to do with the slicing settings that were used, rather than the rods, unless the rods have completely come out of the bearings.

    However, fixing the rods is quite simple to do. For each rod that has shifted, you need to loosen the retaining grub screws in the pulleys at each end of the rod (use the supplied hex keys). Then carefully slide the rod back into place, so it is flush with the side walls of the printer. While holding the rod in place, push the pulley and spacer at one end of the rod tight up against the bearing in the wall of the printer. Then fasten the grub screw in that pulley really tight. Then, making sure that the first pulley/spacer stays tight against its bearing, push the pulley and spacer at the other end of the rod tight up against the other bearing, and again tighten the grub screw really hard. Because the pulleys are now fixed tightly and cannot move sideways, they work together to keep the rod properly in place. The screws need to be really tight, or the pulleys can work loose enough to migrate down the bars, even if they seem, on casual inspection, to be fine.

    Once you have that sorted out, try printing the robot again. Be sure to set a minimum layer time of 7 seconds, and for best results you might want to try printing two robots at the same time, or enable the 'cool head lift' feature in Cura.


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    Posted · UM2: low quality prints due to rod displacement

    Blue shows up errors more than red. Anyway there is at least 2 issues I see on the blue robot.

    1) Levelling looks a bit off - you need to be squishing the first layer into the glass such that the traces are wider than they are tall. I think you need to closer the bed a little closer to the nozzle. Just a tiny bit.

    2) Your overhangs don't look so good. This is usually due to the default bed temp for PLA of 75C. This is too hot. Try 40C to 60C for the robot but I wouldn't go over 60C for this particular print due to it's small size (larger prints might need higher temp. Might.). Other factors that can make overhangs ugly:

    2a) are your side fans coming on by the time it gets 5mm off the print bed? Some people receilved UM2s with the side fans broken. Extremely easy to fix. You can force them on in the TUNE menu which is only available if you launch a PRINT.

    2b) PLA temp might be an issue, lower temps tend to be better but anything from 200C to 230C should be fine for the robot.

    2c) print speed - you want 7 or 10 or even more seconds per layer. If you turned off infill, that's fine but then you need to slow things down a bit - minimum layer time of 7 is good. 15 is even better for difficult overhangs. This is probably *not* your issue as I assume you have infill so I don't recommend touching this.


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    Posted · UM2: low quality prints due to rod displacement

    It seems quite a few of us are having this problem right now!


    The gear/pulleys seem to be made out of aluminum. I would think there is a small chance that tightening too much will damage the threads- the inset hex/allen head screw is made of hardened steel, after all. However, it'll probably be difficult to apply enough force to damage them with the thin hex wrench provided.


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    Posted · UM2: low quality prints due to rod displacement

    The knurled sleeve on the extruder motor shaft is quite thin, and the set screws are tiny - I have seen problems with over-tightening those.

    But I've undone/redone/tightened quite a lot of UM2 pulleys now, and I've never seen a problem tightening them hard by hand with a screwdriver.


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    Posted · UM2: low quality prints due to rod displacement

    The feeder pulley might be tricky but the rest are straight forward: tighten them so much that the hex driver twists significantly.


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