After much hard work and many failed motor controllers, the printer is ready to go. Since leaving school, I've brought all four motor controllers online, etched a heated build plate, added a glass build platform, replaced the Y belt tensioner, printed a ton of plastic squiggles, and calibrated the printer by printing boxes. I plan more modifications, like a holder for the filament, but they're not required.
It's finally ready to print. I'm going to go over the upgrades one by one now. A printed object should show up here soon.
The heated bed and glass build plate both help plastic adhere to the bed. Heated or not, the bed must be coated with either masking tape or glass - neither PLA nor ABS will adhere to most materials. Adding heat helps further: as the plastic cools, it shrinks. The deformation can throw off prints. Heating the build plate minimizes deformation while improving the bond between glass and print bed.
I made the heated plate from a single sided raw PCB, using the toner transfer method. I printed the board pattern onto a page of magazine rag, then cleaned the board and ironed the page onto it. Next, I washed off the paper (the toner remelted, and stuck to the copper). With the board masked, I bathed it in a mixture of HCl and CuCl2. Both compounds remove copper from the board, creating either CuCl2 or Cu2Cl2. With the exposed copper removed, I cleaned off the toner using paint thinner and steel wool, then soldered a thermistor and power lines on. The glass was incredibly easy to create: I found a sheet of 1/16" glass, then scored and snapped it to size. The glass and board are held to the bed with binder clips.
The old belt tensioner was a linear bearing riding on a pen, held down with elastics. Needless to say, it didn't work well. I replaced it with a ball bearing on a threaded rod, with washers to restrain the belt and zipties to tension it.