UM1 layer misalignment

[mahsab 0]

Hi,

 

I've been using my new UM1 without problems, however now I have bought a beautiful white PLA with the only disatvantage that it makes ALL, even the slightest imperfections visible.

 

I have noticed that layers are a little misaligned in the X-Y plane, as can be seen in the picture below. The thickness of the layers is the same.

 

Priting speed, layer heights and temperature don't seem to be making any difference. Neither do the Z-axis speed or vibration (since it was printed at both very high and very low speeds with exactly the same results).

 

Since the layers appear to be even, I susped that the cause could be the Z-axis wobbling a little bit to much and causing the table to shift a little. Can anyone with some experience confirm if this appears to be the case?

 

The brass nut is quite snug (I can't say that it moves freely in X-Y direction), so would in that case the solution be to sand the two pieces holding the nut a bit so it can move?

 

[gr5 2,071]

This is a common problem and it is caused by Z innacuracies. So for example if you are doing 100 micron layers it might only move 70microns and get stuck. Then the extruder extrudes enough PLA for 100 microns in to a gap only 70 microns high and you get a bit squeezing out the side (over extrusion). Then on the next layer you might get 130 microns (meaning it caught back up - it moved the full amount finally) and on this layer you get underextrusion because it is extruding enough plastic for 100 microns but there is room for 130 microns worth.

If your Z screw is dirty, clean it and regrease it with the green grease. Or just add a drop of green grease (a drop about 5mm across). Also put a few drops of thin petroleum oil on each of the 2 vertical rods. Do not grease the rods and do not oil the screw. Try to keep oil and grease away from the outside of the Z nut also - you don't want any lubrication between the nut and the wood (at least I don't think you do).

What layer height are you doing? If you double the layer height you might get better results. Some people have also improved this exact thing by adding a 1kg weight to the bed (under the plastic bed). If you do that you will have to re-level of course.

 

[mahsab 0]

Thank you for your response.

However, as I wrote in my post, the thickness of the layers seems to be very even, meaning they all appear to be exactly 100 or 200 microns thick (whether is 100, 150 or 200 doesn't seem to be making a difference). Rather the layers seem to be misaligned a bit in the X-Y direction (not Z).

 

[IRobertI 516]

Maybe try putting a rubber band from the bed to the outside frame. If the bed is jiggling back and forth perhaps the pull of the rubber band would suppress that a bit?

 

[gr5 2,071]

the thickness of the layers seems to be very even,

 

It's hard to tell that visually because the plastic squirts out the side - I think you would have to cut the part open to be sure.

Before I posted, II looked at a few layers in your picture that stuck out and they appeared to stick out in 3 directions - towards the camera, to the left, and to the right. I couldn't check the back side (or even the sides) very well without having the object in my hand or seeing pictures from all sides. You should pick a layer visually and if it sticks out on all 4 directions then it's probably not your theory of "misaligned in XY direction".

I mean your theory is pretty good - I've heard it before. But from the picture I'm not so sure I agree.

Also this particular problem has come up before and a few people (not all of them) have been able to fix it by simply cleaning the z screw and z rods.

Also you didn't mention what your layer thickness is.