Blobby initial layer

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lesthegringo
Posts: 76
Joined: Mon Dec 26, 2016 9:41 pm

Blobby initial layer

Post by lesthegringo » Fri Jun 22, 2018 2:58 am

Guys, I have commented about this on another thread, but would appreciate any focused suggestions as to how to improve the initial layers.

The first layer comes out as a series of smeared blobs, rather than a smooth straight line. The next few layers get better until by the fourth or fifth layer it is very good.

Adhesion is fine, it's just t h e initial layers are rough

Any help appreciated

Cheers

Les

b-morgan
Posts: 219
Joined: Fri Aug 11, 2017 8:53 am

Re: Blobby initial layer

Post by b-morgan » Fri Jun 22, 2018 6:52 am

My first impression is that the Z-offset is wrong. Try setting it farther from the bed. If the first layer isn't right, the rest of the print is likely to suffer.

Galadriel
Aleph Objects | LulzBot
Posts: 272
Joined: Mon Sep 25, 2017 10:23 am

Re: Blobby initial layer

Post by Galadriel » Fri Jun 22, 2018 8:15 am

It would help to see a few photos of the bottom layer as it is printing to get a better idea of exactly what is happening. This could be a couple different things and having a good visual representation would probably help narrow down a good starting point.

kcchen_00
Posts: 1687
Joined: Thu Feb 19, 2015 12:42 am

Re: Blobby initial layer

Post by kcchen_00 » Fri Jun 22, 2018 8:51 pm

Definitely sounds like the nozzle is starting too close or actually on the PEI. The pressure built up in the nozzle/hotend eventually overcomes the springs and extrudes in blobs/smears. Once the pressure is relieved, the nozzle goes back to being blocked by the bed. And the cycle starts over until the first layer is complete or until the filament is ground through by the hobbed bolt or slips due to a clogged hobbed bolt.

Anyway... if you're lucky your auto-level isn't doing its job. Check that the nozzle and discs are clean of leftover filament, check that the wiper is clean also. Carefully check, it could be a thin film that's impeding the continuity check.

BTW - This is probably the root cause to your "too stuck" print.

I don't own a Mini or a Taz 6... so not sure if homing the Z runs through the auto level process or just moves the Z to the last detected nozzle height. Regardless, try to pass a folded sheet of paper between the nozzle and bed. There should be a little drag / friction.

If you can't pass the folded sheet through, then the nozzle may still be too close. Ensure that the nozzle and discs are clean and the auto-level is working. You'll need to adjust the z-offset in the firmware... this is where I'll have to go research the "MXXX" command to, but hopefully some community member can help out.

lesthegringo
Posts: 76
Joined: Mon Dec 26, 2016 9:41 pm

Re: Blobby initial layer

Post by lesthegringo » Sun Jun 24, 2018 2:30 am

Thanks guys - I fitted my new modular bead and the prints are coming out perfect, so I double checked the old bed and found that the PEI layer, where there were little bubbles between it and the glass, gives slightly, so it was slightly spongy. The new bed, which has no bubbles is firm. Looks like the PEI layer was being pushed up slightly when hot and so caused the nozzle to be partially blocked until the pressure was sufficient to overcome it and allow the ABS to flow.

Lesson learnt there!

By the way, the new modular bed is so much of a better idea and execution - the heater plate has a 'fabric' backing which keeps it firmly in contact with the bed, so no chance of it detaching from the bed like the old ones

Cheers

Les

lesthegringo
Posts: 76
Joined: Mon Dec 26, 2016 9:41 pm

Re: Blobby initial layer

Post by lesthegringo » Sun Jun 24, 2018 11:14 pm

Well, it is definitely something to do with he PEI layer; after only three prints the PEI layer on the new bed is starting to bubble, mostly tiny little bubbles but a couple of spots where you can actually feel that the PEI has a raised surface.

I'm printing Protopasta ABS, so am heating the bed to 110 degrees per the recommendations, but I suspect that this is too high for the PEI adhesive. I want ABS for the strength it has, but it looks like I need an alternative material than can work with a cooler bed temperature, otherwise I will be ending up with an uneven bed surface again

Any suggestions as to suitable alternative materials appreciated, not sure there is anything I can do about the PEI bubbling

Cheers

Les

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