Check this guide for circles, not round
http://support.3dverkstan.se/article/23-a-visual-ultimaker-troubleshooting-guide#circles
As @sandervg says, 99% of the time, is a belt tension issue.
To illustrate the problem. When X/Y short belts ain't tight enough, as soon one motor pushes the other direction, there's a delay on feedback to the shafts due lack of tension, this causes smooth changes of direction to show irregularities. That's why, short belts, must be tight.
Other 1% of the time, the pulleys of umo (not the best quality IMO) use to show eccentricity issues. This means that the curvature isn't perfectly circular. So when two pulleys rotate one pushes more than the other, or both get loose (micro effect). If you look at your pulleys you should actually be able to 'see' that the rotation shows changes showing that the pulley isn't perfectly round. That also can cause lack of precision on very small circles when printing slow. To fix this the best is to move to a GT2 pulley, not only is more precise (UM use GT2 on their um2-um3 but umo/umo+ uses MXL), but also you can get better quality pulleys with less eccentricity.
Remember this might not be your issue. But it illustrate why all mechanicals parts must be as precise as possible to get the best quality possible.
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SandervG 1,521
Hi @Basteluwe,
Thank you for your post and welcome to the forums.
There is absolutely nothing wrong with learning through trial and error. That is what we have all done, and failure is a great teacher!
But luckily you can also rely on the forums to help
The side of your knob definitely looks great!
For the bottom I could suggest to level your bed a little bit higher so your first layer is really squeezed on the bed. That should help in getting that flat, smooth first layer with excellent adhesion.
About the top layer, would you say your knob is perfectly round? From the last photo it looks like it may not be... (maybe that is just the photo..)
How fast do you print?
To be sure, can you check how tight your small belts are?
Thanks, looking forward hearing from you!
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