This design is for a Printrbot with threaded rods at the base, Y and X smooth rods, and a sq. heated bed. The design is ~10.5 in. by ~13 in.
There's also a design that is made up of 4 pieces which attach together with 8 short #6 bolts.
There are 2 pairs of 2 holes for the belt clamps.
There are 4 holes closest to the middle for mounting a x heated build plate.
The 4 holes closest to the outside are for the Y Bar Clamps.
02/17 Update: Made the Y-bar holes wider to allow for some slop in the distance between each of the bases.
02/19 Update: Corrected position of the belt clamps. The belt clamp needed to line up with the edge of the 608 bearings.
02/21 Update: Added length. Hot end doesn't line up with x smooth rods, so there needs to be extra length on the right or left side of the print bed. Also made the holes wider for #6 bolts.
03/01 update: adjusted position of belt clamps
03/09 update: rounded edges slightly
05/01 update: attached a design for a 4 piece print bed, because the laser cutter I have access to can't cut the 13+ inch original design
I'm planning to remove nearly all the material in the center of the plate (to reduce weight/momentum/wobble).