thick prints lifting at corners late in printing

[Tdeagan]

I've searched the forum for 'corners, lifting, curling' but haven't found anything that sounds like this. Apologies if I've missed a previous entry on this topic.

My first level lays down well and sticks (as does the skirt.) Subsequent layers go down nicely. However, on the corners of prints that are thicker than 1/4", about 2/3rds of the way through the job, the corners start to curl up and lift off the plate.

The top of the print remains flat and the rest of the print retains a really strong adhesion to the plate. It _appears_ that the problem gets worse as a function of distance from the center, but it's not consistent.

Printrbot Plus, problem prints are ABS, bed temp is 90 for first level and 95 for subsequent levels.

This picture shows the problem with the corners (and the side extrustions):
curling.JPG

Any help appreciated!
--tim

[drawcut]

This is a pretty common issue. Much of this is from the material cooling at different rates which leads the material shrinking in the cooler areas. The outer edges will cool faster than the interior. People deal with it in various ways, some more successful than others. And there are lots of different ideas and opinions.

First thing: what are you using to get the ABS to stick to the glass? Using something with more sticking power for the thick or long / large parts will help. Of the common sticking agents, I would say that ABS juice is one of the best for a lot of sticking power. Second thing to try would be brim. Brim is basically a skirt of material, one layer thick that extends outward around your part that helps keep that edge stuck down. Slic3r has this feature. Brim is pretty easy to trim off the part after printing. Third you might try using raft. Raft is a base of material, wider and longer than your part that gets printed first and your part prints on that. The raft must then be removed at the end (not always easy). Most slicing programs support raft now. Fourth: maybe an enclosure around the printer to trap heat may help. Especially if you are printing in a cooler area or one with draft. Also you can experiment with your temperatures (and fan usage). Hard to give exact temps to use since most people's indicated temperatures will not be the actual temps. But whether you are indicating high or low, it should remain off by the same amount, so you just figure in your printer's temp offset.

[Tdeagan]

Thanks!! I felt confident that it was tempo related and not confident of much after that

I've been using hairspray on glass as my sticking agent. I'd tried kapton and blue tape, but neither worked half as well as my experience to date with hairspray on the glass. I'll try ABS juice next and the Brim. I'm using Pronterface/Slic3r so that's a great tip!

thanks again,
--t

[eckerput]

I also find turning down my fan helps a lot with this as does turning up the bed temperature. The warmer the piece stays during the the less it will contract. If it contracts while part is stuck to the bed you get curling like you see. Once you remove it from the bed it can all contract evenly and there is far less distortion (but you will still often get some).

[Tdeagan]

I had a (shockingly obvious in retrospect) insight last night while printing. I was printing ABS with ABS juice and a 5mm brim. I'd forgotten that I'd previously applied hair spray (having just switched back to ABS from PLA printing.) The print started curling aggressively (ABS juice does not stick to hair spray worth spit.) The light bulb moment for me was noticing that it was _only_ curling on the end that was getting hit by the fan. The back side wasn't curling at all, but the front was lifting like a magic carpet. My fan is mounted on the front. This makes me __VERY__ interested in changing to one of the ducted ring fan mounts that blows the air evenly down around the nozzle instead of at an angle from the front.

Everyone else may have figured this out long ago, sorry if I'm being Captain Obvious

[Syntaxterror]

Don't use a fan for ABS, unless you need it for bridging and so forth. I only use a fan for pla generrally

[Tdeagan]

On ABS prints where I had really tight corners (e.g gears and other edges with small angle direction changes or tight pointy things such as the working micro heart ,) the fan made a really significant positive difference. Without the fan, the ABS would curl up at the tip of the point or get otherwise discombobulated. With the fan, the point set in place much better.

I've got an inline switch on the fan so that I can easily turn it on and off during print runs. I guess my insight here is that it's really not serving it's best purpose (IMHO) when it's non-uniform in it's cooling.

cheers,
--t

[ivymike1031]

I posted some other ideas with respect to stopping warping and layer separation in this other thread:
viewtopic.php?f=18&t=2790

[Tdeagan]

There are some really good ideas in that thread. De-lamination is a really frustrating experience that keeps coming back. I am _very_ interested in techniques that overcome it!

[ivymike1031]

Thanks...hope it helps
The gaps are a big help for me, when the design allows.