# Any possible issues with adding heat/cool down cycle in the end of print (PLA)

I'm printing with anycubic i3 mega on an ultrabase bed. When I first got the printer the prints were easy to remove from the bed after it cools down, I didn't need to put any extra effort. However after I used 70% isopropyl to clean it it seems I removed some kind of extra coating as all next prints were sticking to the bed firmly even after the bed cools down. So I tried to heat the bed up to 100 degrees and then cool it down and wait until it gets to something like 35, at that point print comes off quite easily (really helped me with some big parts with huge initial layer) so I wonder if I should just add that extra heating cycle to the end of each print job.

Is there any possible problems with that?

PS my understanding is that PLA should be okay with short temperature spike since it is being melted with twice as high heat. However long exposure to that temperature might cause some deformation (eg if I throw the printed part into dishwasher). Another possible concern is that extra heating cycle could potentially shorten life of the ultrabase, but not sure if it is the case.

UPDATE

so after some experiments I printed at least a dozen calibration cubes adjusting several parameters along the way as it seems each of them contributed to the issue

• I decided to reset initial layer thickness which I noticed was set to 0.25 when normal layer was 0.2. Since it was thicker for better adhesion I thought I don't need it since I don't have problem with sticking to the bed :)
• second thing was the flow adjustment and enabling some layer filling settings in cura (filtering small holes etc). Ended up at 91% flow rate which gave me much cleaner top layers as well as the bottom ones.
• and finally I played with Z offset, I did bed leveling recently so it was flat (did single layer tests to check that) but it might have been a little bit too high, so adding an offset seems like a good way to compensate for it. The thing I was looking after as a feedback here is the squeezing bottom layers issue, so I stopped once I got initial layers a bit smaller than the ones on top, went back a few values and ended up with 0.125 mm which sounds quite big to me but it allowed to get initial layer very clean and consistent with next layer so I think I got it right.

I can say it is easier to remove the cube from the bed now (used to be very difficult and I was using a mallet almost every time in the beginning) but it still doesn't come off on its own. I also noticed that now all three dimensions are almost identical (Z was about 0.5 less). And all X/Y/Z are ~19mm after cube cools down (the model is 20mm) so I wonder if I need to fix that one now

• I only know of layers added to promote adhesion, not release. – Perry Webb Jun 29 '20 at 16:39

Heating PLA even to 60°C will make it pliable and may affect dimensional accuracy; 100°C is likely to make that severe. Being stuck to the bed and thus constrained by it might help some, but I think it's a bad idea.

If your PLA is hard to remove, you probably have bed leveling issues. PLA should remove easily after cooling from reasonable print-time bed temperatures of 40-60°C to room temperature as long as it has not been extruded against the bed with excessive force (from being too close and having nowhere else to go).

• hmm, didn't think it could be caused by bed leveling since it wasn't changed when models stopped come off, I did check the bed level recently and it seems like it is at least flat so I will try to add some Z offset to compensate and check if it helps, thanks for the idea – Leo Jun 29 '20 at 3:17
• Don't just poke at things, measure. Print a 2-payer square with 0.1 mm layers and measure with a caliper that it's within an acceptable margin of 0.2 mm (e.g. +- 10%). – R.. GitHub STOP HELPING ICE Jun 29 '20 at 3:22
• I think I partially solved the problem with adhesion. Will add details to the body of the question. Thanks for your answer though, it made me think in another direction and look for the root cause which I think I found – Leo Jun 29 '20 at 22:47

You did exactly the right thing:

1. look,
2. see,
3. think,
5. test
6. Back to 1. or continue to 7.
7. Solution found and applied!

Congrats! Johan

Ps: I use the tape in paper, used to mask before paint jobs, I was not that keen as you! It always comes off, and I restart every time with a clean glass, no hairspray, glue or others. They cost nothing, and if you are handy, you can use 100mm wide stripes. (or just the amount needed for your part.