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Troublle with curling corners (with pictures)

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This is a very common problem with very easy solutions (curling corners). The problem is that the material shrinks as it cools and as the upper layers cool (say 2mm above the base) it is pulling hard inward like bungee cords pulling the walls inward. This causes the corners to lift up. One (not necessary) solution is to keep the air at the glass temperature for the material you are printing which for PLA this is about 50C. But this is not the best solution - the best solution is to just make it "stick like hell" to the bed.

On the UM2 you should be printing on glass.

1) Make sure the glass is clean if you haven't cleaned it for a few weeks. You want a very thin coat of PVA glue which is found in hairspray, glue stick, wood glue. If you use glue stick or wood glue you need to dilute it with water - about 5 to 10 parts water to 1 part glue. So for example if you use glue stick, apply only to the outer edge of your model then add a tablespoon of water and spread with a tissue such that you thin it so much you can't see it anymore. wood glue is better. hairspray doesn't need to be diluted. When it dries it should be invisible. This glue works well for most plastics.

2) Heat the bed. This helps the plastic fill in completely (no air pockets) so you have better contact with the glass. For PLA any temp above 40C is safe. I often print at 60C bed.

3) heat the bed (didn't I already say that?). Keeping the bottom layers above the glass temp of the material makes it so the bottom layers can flex a bit (very very tiny amount) and relieve the tension/stress. For PLA 60C is better than 50C. 70C is even better but then you get other "warping" like issues at the corners where they move inward but if you are desperate it's worth it. For ABS you want 110C (100C is good enough).

4) rounded corners - having square corners puts all the lifting force on a tiny spot. Rounding the corner spreads the force out more. This is optional if you use brim.

5) Brim - this is the most important of all. Turn on the brim feature in cura and do 10 passes of brim. This is awesome.

If you do all this you will then ask me "how the hell do I get my part off the glass?". Well first let it cool completely. Or even put it in the freezer. Then use a sharp putty knife under a corner and it should pop off.

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By the way - doing only #5 or only #1 might be enough for your particular models but if you use all 8 inches of glass you will need all the methods. I left out #6:

6) since it is the upper layers that are pulling it inward, try to reduce this by putting large vertical holes through your part. Of course for your models this is bad but for say the arm of a quadcopter this will not only reduce lifting but reduce wasted material without reducing strength.

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I have seen loads of suggestions, and tried a few. By far and away the best one so far that works for me (might not work for you, your sister or the pope) is spreading UHU branded glue stick over the bed with the temp as 100C. Slathering the stuff on. Twice. In two directions. Then I check for spots I missed using a torch and add some more.

I found UHU glue to be better than the stuff that came with the printer and some cheap garbage I bought at the local discount store (the cheap stuff is actually quite good for PLA, but right now I'm in ab ABS mood).

Now you won't get a shiny bottom surface, but if your bed levelling is good, then the PLA will stick like crazy on the stuff. Trying to pry it off with a tool will cause damage to the print, will probably cause damage to the printer and when you stick a razor sharp blade in your finger during the removal process you will begin to wonder what you were thinking of.

So how do I get the prints off? I wait for the plate to cool down. If I have printed ABS, then some 20 minutes later they will usually pop off themselves due to shrinkage. With PLA, I have to tug a little, perhaps employ some dubious language or as a last resort freeze the plate and the the prints come right off.

Again, this might not work for you. However, if all else fails or does not seem appealing to you, try this. You might just be surprised. Or shocked. Depending if you are earthed or not :-)

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