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Z-layer Error / Skipping Layers - Sharing Experience

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So I've been using my UMO+ for about a month, and since day one I have seen what looks like skipped layers on my prints, especially when using higher resolutions such as 0.1 mm or better. The skipped layer is always around the same height, at ~12 mm.  Sometimes there are two skipped layers.

I wanted to share my experience and solution on the issue.  Hopefully this posting adds to all the other postings on topic rather than being a repeat, and maybe it will help someone else with a similar situation.

After some research, I narrowed the skipped layer issue down to the Z linear bearings.  When I built the system, the bearings were crunchy and sticky in several places along the bed travel, as many others have noted.  There was an especially bad sticky area right around the 12 mm height zone.

I tried all the recommended fixes: realignment of the bearings (no change), wiping the oil from the shafts (no change), light oil on the shafts (not recommended, and it got worse), and degreasing the bearings and shafts in place (slight improvement).  As a last resort I detached the bearings from the platform, and even with no load on them, they were sticky in several places.  I degreased them further and there was minimal change.  I even flipped the shafts to rule out a shaft problem. I tried everything I could to make the OEM bearings work better, but no luck.

Since I had already ordered and received replacement bearings from Misumi (part no. LHFSW12, 40USD for two shipped in the US), I gave up on the originals and tried the Misumis.

What a difference!  The bearings glide smoothly on the shafts with no sticking.  Now I am happy!

The OEM bearings were OK when held horizontally, but terrible when held vertically as they are installed in the printer.  Orientation of the shafts with the Misumi bearings made no difference.  The Misumi bearings are a drop-in replacement using the existing screws.

Here are some before and after pictures at various layer heights for the 3DHubs Marvin test object.  I used the standard Cura settings for Low, Normal, High and Ulti-quality, except that I changed in-fill to 10%.  The material is 3D Universe Grape PLA, 210°C nozzle/60°C bed.

Before (with OEM Z bearings):

5a33213b3b5fb_PrintTest-front_Before.thumb.jpg.207476eba8621d77be03b91fd5626705.jpg

5a33213b6a4ce_PrintTest-back_Before.thumb.jpg.d52216ea4e713b3c47cfbad5371cdae7.jpg

Note that there is a skipped layer on the 0.1 mm and smaller prints.  The skipped layer is at about the same height on each print.

After (with Misumi Z bearings).  Note: I should have leveled the bed after the bearing change, so my first layers on the first three prints weren't very good.  For the 0.04 mm print, I leveled the bed:

5a33213b910ab_PrintTest-front_After.thumb.jpg.a39e9cc5588854053ceb7d487ac26b26.jpg

5a33213bc1888_PrintTest-back_After.thumb.jpg.bcf4b4778e47a549577dea9078ebd2b7.jpg

The skipped layer is completely gone on all prints.

Here is the OEM bearing (left) and Misumi replacement (right) for reference:

5a33213be742c_Z-bearingComparison.thumb.jpg.3b1f70033b397d15b8400f99e4461f90.jpg

As a result of this work, I highly recommend the Misumi replacement Z bearings.  I wish that Ultimaker had used higher quality bearings in the kit, since this appears to be a fairly common complaint.  Both of my bearings were faulty, so I don't think this is a random occurrence.

Best Regards to the Community.

5a33213b3b5fb_PrintTest-front_Before.thumb.jpg.207476eba8621d77be03b91fd5626705.jpg

5a33213b6a4ce_PrintTest-back_Before.thumb.jpg.d52216ea4e713b3c47cfbad5371cdae7.jpg

5a33213b910ab_PrintTest-front_After.thumb.jpg.a39e9cc5588854053ceb7d487ac26b26.jpg

5a33213bc1888_PrintTest-back_After.thumb.jpg.bcf4b4778e47a549577dea9078ebd2b7.jpg

5a33213be742c_Z-bearingComparison.thumb.jpg.3b1f70033b397d15b8400f99e4461f90.jpg

Edited by Guest
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Thanks neotko!

What are the "Cost Effective" Misumi bearings? All I did was search their site for the LHFSW12 bearings and bought those for 16USD each. I didn't want to take a chance on cheap bearings so I just paid the price. At any rate, I would think that the Misumi lower cost parts would also be good, since they are a reputable company. Had I known about them, I would have considered them.

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Thanks again. Just for grins I tried to look up the C-LHFSW12 bearings on the US Misumi site, and I couldn't find them. So I went to the Misumi Europe site and there they were for 6.57€ each. I guess the "Cost Effective" product line is not available in the US.

Well it doesn't matter at this point since my bearings appear to be working well.

I know that people have said that the "crunchy" noise is normal, but in my experience with motion systems, it's not. The fact that good quality bearings are not crunchy shows that.

I think that Ultimaker should consider putting better quality bearings in their products from the start--especially the UM2, which costs 2.5x of a UMO. Maybe it would cost them 10€ extra per machine, but their quality reputation would be maintained.

In my case, since I chose to build my UMO+, I expected some issues like this, so it doesn't bother me that much. My wife thinks I'm nuts though--first for buying the machine and then for tearing it apart and putting it back together :). But there are even more ideas for optimizing my system that I am learning from this forum. That's all part of the fun for me!

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My wife thinks I'm nuts though--first for buying the machine and then for tearing it apart and putting it back together :)

 

Lol I know that felling. On my umo+ I changed so much to push the quality as much as possible.

Z bearings are a good upgrade. I know that Ultimaker, while sometimes doesn't post directly, they hear pretty much everything we post.

My favorites mods for umo are

- GT2 belts/pulley

Better movement accuracy and being able to keep 180mm/s travel speed at all times.

- Um2+ Hotend upgrade

Slightly better print quality, nozzle swap fast and reliable (umo aluminium degrade/break after the 15-20 nozzle swap) and TFM coupler last 500-2000 print hours (so less maintenance)

- Big x2 40x40x20 fans to make really almost impossible overhangs. A bit too much, Gudo mod for um2 hotend it's probably better in terms of weight (check his youmagine)

- Move z endstop to the bottom + new firmware. Allows to change z offset by firmware.

- And my longtime favorite,change the hotend to 1.75mm filament with IRobertI + mk7 or FatIRobertsI + cheap bondtech kit.

Check my youmagine for some of this mods :)

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Check my youmagine for some of this mods :)

 

I will check out those mods. I am also looking at a modified fan duct for the single fan with a nozzle insulator, which I will post if successful. I want to improve printing the overhang on the far side of the Ultimaker robot by creating a more even cooling airflow, but with just one fan, if possible.

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