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poshman

UM improvements in place - Resoltion now :+-0.05 mm - Happy!

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So finally I got around installing UM upgrades.

Calibrated my machine and I'm very happy to say I reach a resolution of +-0.05 mm. Actually more of measure error... :D

So what have I installed:

Direct drive. I bought a set of GT2 pulleys, belt and new 8 mm axes.

I created a simple but sturdy enough holder for the motors. The setup allows for mounting the brackets first, attaching a part to a motor and then fixing the motor. Also leaving a bit of self adjustment due to some slack in the holes (just for alignment during mounting).

Direct Drive setup

Direct Drive setup 2

I installed Chopenmeister "twister blocks" and design a new belt clamp that fixes and gives tension to the GT2 - belts. However, I do want to redo the fixing of the parts. For now it is satisfactory.

Belt Adjuster used together with Chopenmeister twister blocks

GT2 Belt Clamp

and then I also installed my heated bed in a bit more professional way. Well, could have looked a little bit better but what the heck, the machine is supposed to deliver prints, not good looks.. :smile:

After everything was installed I calibrated the x-and y-axis regarding traveled distance to number of steps. Now when I print a part that is 100x100x10 mm I get a very good reproduction. 100.2+-0.05 in x-direction. 100.6+-0.05 in y-direction, and 10.0+-0.02 mm in z-direction.

An interesting part i have noticed now when I calibrated my UM is that circles tend to be 0.2 mm less in diameter than they should be. I included some circular patterns using the same diameter along x and y-direction.

Calibration part

This is quite interesting.. Everything else comes out just fine, but circles are to small. I have tried on other slicer (Simlify3D) and it produces the same results. Is this something that has to do how the slicer calculates circles ???

 

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Very nice work! Did you do the changes (direct drive, GT2 belts) all at once or one after the other. In other words, can you guess how much improvement came from the direct drive and how much from the GT2 belts? I currently have a direct drive but still the original MVL belts.

[...]

This is quite interesting.. Everything else comes out just fine, but circles are to small. I have tried on other slicer (Simlify3D) and it produces the same results. Is this something that has to do how the slicer calculates circles ???

I guess the circles are about 1-3/10 to small, aren't they? It's a question of shrinkage of the PLA. You have to correct in the model. As you do in injection moulding.

btw: are you not afraid that the PSU of your heated bed radiates a bit too much a the PLA gets soft on the spool? Or is it not PLA?

 

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Very nice work! Did you do the changes (direct drive, GT2 belts) all at once or one after the other. In other words, can you guess how much improvement came from the direct drive and how much from the GT2 belts? I currently have a direct drive but still the original MVL belts.

I guess the circles are about 1-3/10 to small, aren't they? It's a question of shrinkage of the PLA. You have to correct in the model. As you do in injection moulding.

btw: are you not afraid that the PSU of your heated bed radiates a bit too much a the PLA gets soft on the spool? Or is it not PLA?

Thanks,

I did all the changes at once. The pulleys on the UM i received were not reaching for high precision... so I bought the GT2 instead. In the old config I printed the rest of the parts and then I started the rebuilding.

The PLA will not get affected by the PSU. It leaves very little heat and as I have mounted it vertically the excess will not pass the PLA in high degree. If I would consider the PLA being affected it will not result more than tops 1/2 degree.. Nothing to worry about.

The next step is to modify the tension devices a bit. I'm thinking of making one of the sides fixed and just one being used for tension. The only drawback from this is that it will be slightly more difficult to mount the belt. Or - I will just change the holding mechanism so the they are straitened out more and so that I perhaps do not need the clips over the belt. However, the clips works fine..

One thing I'm curious about is how come the holes are affected and not the whole part? If the PLA shrinks all of the part should shrink. Now the outer measurements fits perfect but the holes do not. 1+1 does not add up here... or have I missed something?

 

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[...]

One thing I'm curious about is how come the holes are affected and not the whole part? If the PLA shrinks all of the part should shrink. Now the outer measurements fits perfect but the holes do not. 1+1 does not add up here... or have I missed something?

The outline shrinks only a bit because the whole infill gives quite some resistance to this shrinking which is not the case for holes. But you also get significant shrinkage of the outline for thin walled hollow prints.

 

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The outline shrinks only a bit because the whole infill gives quite some resistance to this shrinking which is not the case for holes. But you also get significant shrinkage of the outline for thin walled hollow print

I have to test that - hollow parts - to identify how the shrinkage occurs.

If it comes down to shrinkage I definitely have to do something about my fan. It is way to "unfocused" . I Think I will try some variant of cross-flow maybe combined with a improved fan shroud.

Have you improved your fan, and in such case - did you see any improvement?

Regarding the major improvement in precision I believe that in my case it comes from changing the pulleys and getting new shafts. My old pulleys wobbled a due to the through hole being 0.1-0.15 to big, and not always centered. Moreover, the original shafts were not straight enough. Besides from that, If the short belt arrangement would have been sturdy enough I would have kept them. Now I do not have to think about belt tightening. I never had any problems with it though.

 

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Is this something that has to do how the slicer calculates circles ???

 

Nope. There are 3 causes but in fact the slicer path will be .4mm larger in diameter than what CAD shows to compensate for the radius of the nozzle of .2mm on each side. The causes:

1) Shrinkage as people said. It sounds like you adjusted your steps/mm to account for this so it probably is not an issue in your case. Having infill does *not* prevent shrinkage - if anything it encourages it, pulling the sides inward.

2) segments in a circle. If you print a circle with 4 segments the cad software is cutting through the circle severely. The more segments the closer you are to a circle but even with 20 segments you are cutting into the circle a bit. So unless you have 100 segments you will probably see some minor "cutting in" due to that factor.

3) viscoscity and stickyness and pulling inward by the nozzle. The PLA while it comes out as a string is getting pulled towards the center of the circle as the nozzle goes around the edge. This places the PLA more inward than desired. This effect is stronger on smaller circles (pulls in more towards the center). It seems like the slicer could do some kind of "pulling in" compensation which might change for different types of PLA, nozzle temp, fan speed. The factor would somehow get stronger for small circles and weaker for larger ones.

Most people however just print critical dimensions twice. The first time for practice, then update your cad model to compensate and print again. After a while you can build up a set of rules of how much to compensate for your typical printer settings.

 

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