The kinds of materials you’re printing with also make a difference, with the most common consumer-level options being the durable Acrylonitrile Butadiene Styrene (ABS), strong but flexible nylon, and the widely used Polylactic Acid (PLA).
Stuck ABS can be dealt with using either heat or acetone, though acetone should be a last resort as it could damage the printer’s PEI sheet enough to make it unusable. So instead, try heating the printer bed to 100 degrees or more to soften the ABS bits, then gently remove them with a plastic or silicone scraper.
Taking care of nylon is a similar matter, except you’ll want to stick with heat only (no acetone). Typically a heat gun will do the trick, so long as you can get it to around 375 degrees Fahrenheit (190-degrees Celsius). Just hit the nylon with the right amount of heat to get it melting, then carefully peel it off the bed using a plastic or silicone scraper.
PLA is also a lot like dealing with ABS, but this time around you should wait for the printer bed to cool down before you start cleaning. Once it’s cooled, use a plastic or silicone scraper to peel up the plastic residue. For stubborn bits, use a clean wiping cloth with a bit of isopropyl alcohol to gently wipe down the surface of the bed.
