PLA and layer adhesion

I'm trying to print what is essentially a large (100mm x 200mm x 40mm) block with a couple of large cutouts that go down to 3mm above the bottom surface. The problem is that when attempting to remove it from the bed, as soon as I start to get a thin blade under one corner, the bottom layers rapidly seperate from the infill all across the block and the top of the part comes off, leaving the bottom solid layers stuck to the bed. I've printed some larger parts with ABS, but this is my first big print with PLA.

Using blue tape on a glass bed at 60C. First time I tried printing it, I used 2 bottom layers and 20% infill, 190C. Second time I used 4 bottom layers, 30% infill, 200C. Both times the cooling fan kicks on after the first layer. Both times the part failed where the bottom layers end and the infill begins. Managed to salvage the 2nd print with a lot of superglue, but still...

Any suggestions on either how to get the infill to stick to the bottom layers? More infill might stick better, but the additional stiffness might offset that.

And since it's game day today: Beak 'em Hawks!

I've had PLA prints fail due to poor layer adhesion at 200C but succeed at 205. I've also had prints fail due to extrusion width being too small. My go-to settings for PLA are currently 205C, 0.5mm extrusion width, 0.2mm layer height with a 0.4mm nozzle. You could try increasing the temperature slightly to see if that works; I would also play with extrusion width: it should be greater than your nozzle diameter. layer height should be no more than 80% of your nozzle diameter.

From my very limited experience, PLA is more brittle than ABS. Perhaps its that aspect that is at play here?

Never had any luck with blue tape ,i use hair spray directly on the glass with no problems.

Also try increasing your wall thickness. In terms of base plate adhesion, Elmer's glue stick all the way - best solution out there by far.
cheers!
-d

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Originally Posted by Wolfie

From my very limited experience, PLA is more brittle than ABS. Perhaps its that aspect that is at play here?

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how ?
I'm not hitting the parts with a hammer :0)

It's actually more a case of vacumn adhesion versus actual grabbing adhesion.

Things stick to flat tapes and glass mainly because of vacumn adhesion. Whereas bluetape supplies a rough surface that the plastic penetrates and bonds into. Likewise the vinyl in hairspray gives active grab.
I don't have glass - I have aluminium and when I get round to making swappable plates, I will definitely be trying the hairspray thing. Just not right now :-)

So I think my next attempt will be back with blue tape. Never had anything detach from that while printing.

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right. Going for overkill. heated blue tape and a real tight calibration.
Applied the tape with the bed heated as well for extra stick.
Also decided to do one piece at a time.
And back to makerware - the infill i got from s3d was just woeful, even with boosted width and this thing needs to take some real weight.

Phew, one of te problems with makerware is the slicing sucks on overhangs. I generally get bits sticking up that the second nozzle catches. You never get these with simplify3d.

Fortunately I was here when the bloody things started catching. A few pauses and a swift application of a file and we're back to no catch printing. Should be good for the rest of the print now :-)

well that's odd. I posted with pics this morning. and it's not there now. weird.

basically bluetape stuck to pet tape on ahot bed - will stick any print. The hard bit is removing the print lol

But I do now have a fully working leg.
Interesting thing the blue tape bonds that well to the pet tape that both are coming off together.
Which means that prints cannot pull thebluetape up like they might normally do.
Did two prints - about half the plate covering destroyed in removing both prints. lol

This could be the ultimate non-warp, total stick, one use, bed covering :-)

Should have enough intact covering left for the second foot :-)
Might have a go at printing the second leg outer on the knp as I've got the cooling duct fitted now.