Warning: TLTR, possibly confusing, and definitely frustrating.
Shrinkage from air-cooling is the problem. Straight line perimeter walls very prone to this. Overhanging perimeter wall, especially corners, are going to be difficult.
- Blue tape is coated with a sealer, so should be lightly sanded w/240grit, then cleaned w/alcohol. As Tanya suggested, add “ears” to the corners. (they come in different sizes). Cut them off later.
- Use a Removable glass plate, instead of tape (adjust Z-height home to compensate for glass thickness) Apply "Aquanet Superhold hairspray, 6 light-thin layers for new glass, allow to dry for each application(tip: use hairdryer), then just 1 application for “seasoned” glass(allow to dry). Pop finished print in to the freezer for 2-3min, and the object will remove effortlessly.
This only work for me, for objects up to 2-3 inches wide.
- use ABS Slurry, on removable glass plate. (you can do it on the U2, but it’s messy, and I don’t like accidentally pulling on the bed-springs, while trying to remove the print from the glass-bed)
This is the BEST solution for larger objects. (I test-printed a 8x6x1/2" slab of ABS, and it stayed perfect flat). Paint it on fast and thick. This becomes your “sacrificial” 1st layer, as it will “pre-shrink”, once it is dry, and your 1st will bond to that base layer, better. It isn’t very smooth, so you will have to start your actual 1st layer of your print, about +0.2or+0.3mm, above the bed.(typically 0.1mm, for .2mm L.H.)
If you continue to have issues with warping corners during the rest of the print, here’s a few more tricks:
- Modifying the printer, with a Fully-Enclosed build chamber, will help to trap heat and reduce the possibility of warping.
- Find a appropriately size plastic storage bin to fit the top of the U2, cut a slot out of the back,
big enough to accommodate the cables, (thru all it’s possible movements).
- Add a clear acrylic front door.
- Interior ambient-air temp should be 100-110F(37-43C). I temporarily add hot air to the chamber
(w/ hairdryer) , while the bed is coming up to operating temperature.
Top-secret, crazy, and possibly dangerous trick: CHEAT! lol. I use my secret weapon, called the “Flatula”, (like spatula),(defined as: “flat you shall lay”) for corners that are misbehaving, It’s a piece of flat metal, 12"long x 3/4"wide x 1/8"thick. By placing the cold metal, on a hot-soft corner, “while the machine is operating, and on the other side of the print”, you can help to temporarily flatten a “lifting-edge”. (did I mention “risky”? = yes)