Seeking perfection: Circles

[Vectorious 1]

Hey guys,

I recently got my UMO+ and finished Assembly this week. I had some minor problems finding the perfect settings to get nice prints and was quite successful with the help of this Forum! But there is still something which bothers me alot and I cant find a solution. If I I print circular structures I always end up with something slightly not circular (see pictures).

With the 3DBenchy chimey it was the worst and I started looking for solutions. I already checked belt tension/improved belt tension for the long and short belts. I rechecked the pulley positions, played around with print speed, extrusion speed and so on and it seems like I couldnt get rid of the error.

The Euro coin calibration pieces are the last things I printed and you can see that the circles are still not round. I dont know any further and I cant find more things I could do online.

Do I have to change the x/y travel distance to solve this? Everything else seems perfectly fine (rectangles are rectangular and so on)!

Thank you in advance for your help and ideas!

[neotko 1,417]

Check this guide. Most probably your short belts ain't tight enough

http://support.3dverkstan.se/article/23-a-visual-ultimaker-troubleshooting-guide#circles

[Vectorious 1]

Check this guide. Most probably your short belts ain't tight enough

http://support.3dverkstan.se/article/23-a-visual-ultimaker-troubleshooting-guide#circles

 

I already followed this guide before I posted here and was not successful (although I didn't lubricate the rods). I also tried printing very slow (20 mm/s) but the print maybe slightly improved.

[neotko 1,417]

Ok then

Recheck all your assembly, and go for the fine tunning like..

- Check x/y are perfectly square

- Check pulley vs shaft are perfectly align so the belts move smoothly to avoid any extra backlash

To illustrate this part:

- Make sure that tension on the belts is the same (at least feels the same) on both sides of the belt, if not, maybe the wood clamp on the belt is pushing too much pressure on the up side and too little on the bottom side. Fix for this should be release the pulleys, and let the belt tension adjust itself. Ofc there's also a gazillion umo+ belt tensioners.

Your machine need's oil, indeed, from day one, specially since after assembling it you might have put dirt, hand grease, wood dust, on your shafts. Is a very good idea to put a drop of oil on the shafts, and green lube on the Z bed lead screw.

[Vectorious 1]

Hey,

First of all thank you for the advice! I checked the alignment and ajusted it (was not too bad though).

I also checked the belt tension and printed belt tensioners and installed them.

Z-Stage is lubed quite well and I am waintig for the sewing maschine oil to arrive so I can oil the shafts.

I checked if x/y is perfectly square and so far it seems like it is.

But well.. As you can see in the picture the sitution did not improve (left is before right is after adjustments).

What I did not really understand was the wooden clamp thing with the uneven pressure. You mean the one in the sliding blocks holding the belts? And how should the belt tension adjust itself?

[neotko 1,417]

I think the short belt tension might need moar tension. Did you check them?

Also, since you are using default mxl pulley/belt, afaik umo pulleys are really bad. I remember a number of issues until I upgraded to gt2. Specifically the wooble they can do when rotating can make all get backlash.

This has been an issue on umo/umo+ sinxe the beginning https://ultimaker.com/en/community/2611-fixing-pulley-innacuracy#reply-14503

I think most of us went and just upgraded

https://ultimaker.com/en/community/15874-mxl-vs-gt2-print-results

[Vectorious 1]

Short belt tension was the first thing I checked and adjusted before I posted here. I will disassemble the printer a bit and will test the sliding of the sliding blocks individually now.

I already saw another post (of you I think) talking about the gt2 pulleys and I will definitly do that! I just thought that the original ones are not so bad that they cause the uncircular circles. I also planned to uprgade the sliding blocks but since I have to print them and they have round structures in them I am afraid I have to fix my problem before.

My last hope is that lubrication will solve the problem..

Anyway, thank you for your help!

[neotko 1,417]

Lubrication will help to avoid backlash but is just necessary to make all work.

The eccentricity of the pulleys can (and do IMO) make backlash on the shortbelts, because that changes/swifts the distance of the belt, creating the backlash.

For me the most visible improvement was the gt2, because they are better for fast changes of directions (jerk moves) and specially because even most china ones have better eccentricity than the ones supplied on any of my 3 umo+. Ofc you could get new ones, but since gt2 is quite cheap upgrade, is worth the trouble.

[Vectorious 1]

Ok I am slowly getting where I want and I think I found the source of the error.

First I loosens all the sliding blocks and pulleys and tried to check for friction but found that everything worked quite well. In the end I reassembled everything double checking belt tension and pulley positions. I again adjusted the short belt tension and test printed again. (bottom one is the latest print)

Now at least the gaps around the circle are closed! But unfortunately it is still not perfectly circular.

Anyway. While printing I sometimes could hear a light crack (like wood tension cracking) at certain positions and tried to find its source. Well, it turns out that, as you already said, the pulleys are super eccentricity and the light cracking occurred when the tension on the short belt was slightly increased by this. I will now decrease the tension again to not stress the parts too much but I already ordered the GT2 ...

Thank you for your help and your advice!