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I am currently using Ultimaker 2+ to print some big parts with PLA. As long as the printing lasts for less than 15 hours (that's what I observed by experience, approximately), there are no problems. If the duration of printing is greater than this time, the part would get shifted from its initial position. It looks like the part is not sticking to the bed anymore.

I was first using classic glue sticks and this problem occurred. Next, I tried with different masking tapes but the problem remains the same. The glass bed is not heated. The first layer and the following are actually pretty clean. I use brim. I reduced the printing speed to 20 mm/s on purpose to see if it would reduce the probability of this phenomenon to occur. However, this is not the case.

Do you have any experience concerning this problem, ideas, suggestions?

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  • $\begingroup$ Do you see any lifting or "peeling" of the work, especially at the corners of the bottom layers, where it's starting to leave the bed? $\endgroup$ – Carl Witthoft Apr 10 '19 at 13:24
  • $\begingroup$ Start a square vase mode tower. After the first few layers take a black marker and put some "witness" marks from the bed to the part in a colour that can be easily seen. After it fails check if the line is now broken. $\endgroup$ – user77232 Apr 10 '19 at 14:04
  • $\begingroup$ If you are having trouble with adhesion, your brim will warp up off the bed. Are you sure you aren't getting power surges or something occurring on your computer.? I've seen this with a power surge. $\endgroup$ – Perry Webb Apr 10 '19 at 21:48
  • $\begingroup$ For long prints on a RepRap, I print from an SD card to prevent events on the computer from interfering with the print, especially when the computer is unattended. Don't know if you have that option. $\endgroup$ – Perry Webb Apr 12 '19 at 20:27
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If the brim is firmly connected to the part and sufficiently large, you could "duck tape" the brim to the bed after a few hours; by then you should have enough space/clearance to work with.

But maybe the best advice is to invest in a heated bed platform, or use the heated bed if you only did not enable it. Heating the filament to the point close to the glass transition temperature ensures that the printed filament stays ductile. Once filament cools down, it shrinks and cannot grip on the to build plate indefinitely.

My Ultimaker 3 uses a heated build platform that can virtually make every filament stick to it as long as you prepare the bed correctly. On glass I prefer to use a specifically designed printing spray called 3DLAC; that, and a little heat (depending on the filament you print; i.e. the glass transition temperature) make that I never have had any problems with getting filament to stick to the build plate. I'm even able to get the slippery filament POM to stick to the heated bed.

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  • $\begingroup$ I agree with trying to tape down the brim. Just warning that if there's extreme curling or lifting of the bottom layers the tape may not hold (I know from sad experience) $\endgroup$ – Carl Witthoft Apr 10 '19 at 13:25

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