About a year ago, I designed a bracket for the Printrbot Play that utilized the full size of the bed using some longer smooth rods. I recently built another Play but this time with a barebones kit and a bed that was missing its holes. I decided that instead of drilling my own holes and buying a heater PCB, I should try the T15x23 beds made for old Flahsforges.
It fit perfectly (after removing the wire connector, soldering directly is safer anyway) and just needed some brackets to mount them to the rods. This design uses M3 screws and captive nuts. I cut the screws to length and you want about 28 mm for non-countersunk screws, maybe 28-27 for countersunk. You also need to remove the Z motor screw that's closest to the bed. The brackets are tall enough that they should keep the wires for the heated bed out of the way.
This is too large to be printed on the stock Printrbot Play. This is perfect for someone who has a play but finds its build volume a bit too restrictive, so they have another printer that they use most of the time.
2x 300 mm smooth rods (look on ebay or aliexpress)
T15x23 bed from RepRap Champion (also available on Amazon)
4x 28 mm m3 screw
4x m3 nuts, preferably lock nuts
GT2 belt (I'd recommend just getting 5 meters if you don't already have some)
Zip ties for the belt and bed wires
Cable sleeving helps a ton for keeping the bed wires out of the way as well as kapton tape for giving the wires more support and taking strain off the solder connections
Pretty easy to print, just make sure the side with the nut holes is facing up so there are no overhangs. Make sure infill is set to grid. Using rectilinear means it prints infill in alternating directions every layer, vs grid that does both directions every layer which gives you substantially better internal layer adhesion.I printed mine with 2 perimeters/shells but you could do 3 if you wanted to be safer, though the part is mostly only under the stress of the belt. I printed mine in PLA and I see no need to print it in ABS or any other higher strength plastic.
I was kind of lazy with this design and originally designed it for some leftover rods that are 303 mm. This was super easy to design and if you want something better, I implore you to make something better. You can import the STEP file into Fusion 360 and project most of what you need like the rod and belt holes. The Play files are here: https://www.youmagine.com/designs/printrbot-play-model