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SQuicke

First layer bobbling

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I'm printing with Ultimaker White CPE and the first layer is bobbling.  As you can see if the attached pictures the printer has printed half the first layer from the center to the outside then moved back to the center to print the other half of the first layer.  The bobbling does not seem to have carried over to the second half of the print.  Does anyone know if this is a bed level issue or possibly an adhesion issue?  The bed has not been leveled in a month or so but the auto level runs every week so should this not help keep the bed level?

The printer is a UM3 printing CPE white (default settings) 240c Core, 80c BP.

Clean glass, hairspray

Thanks in advance

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Edited by Guest

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I don't have an UM3 and haven't printed with CPE, so the following is from experience with PLA and PET. Usually this sort of defects comes from overextrusion. Or, if it is on the first layer only, it comes from the glass being a bit too close to the nozzle: the advantage is that the layer is squeezed well into the glass, usually with better bonding as result.

I also see brown spots on the print. So I would guess that the blobs come from molten material that is accumulated on the outside of the nozzle while printing (thus due to overextrusion or the nozzle being too close to the glass), and that sags and falls off on the print. The brown is when it starts to get burned.

Usually big light brown chunks and strings come from burned material on the outside of the nozzle, while thin black chips come from the inside, in my experience.

Try printing a small test piece, for example a cube of 15mm x 15mm x 15mm, 100% filled, and see if it still happens after a few layers?

Stay with the printer and watch what happens under the nozzle.

Bad bed adhesion also causes a sort of bobbling, but as far as I experienced, it looks a bit different. If it would be bad bed adhesion, that should clearly be visible from the bottom: there should be indents, like the shape of water drops, but then hollow.

All this is a guess, but it is an educated guess. :)

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Thanks Geert. From what you have said it does look that the nossel could be a bit close to the bed. I might try reducing the extrusion rate for the first layer and see if this works, then I will have a bit of a fiddle with the bed height and see if I can get a better layer :)

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What I have observed, original CPE profiles with original CPE materials on UM3 are TOO overextruded in Cura 2.5/2.6.x. And it's not about the 1st layer, I have big issues described by @geert_2 with CPE in higher layers too. Unfortunately, if I have experimented with lower extrusion, there are visible gaps between walls and infill. So it calls for deeper changes in CPE profile.

EDIT: The overextrusion is more then visible on large models (across whole heated bad) with the standard profile for CPE and 50 %. I am trying to do some tests with manual reducing of material flow.

Edited by Guest

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