From Thingiverse description:
This is my own variant of a variety of 3D printer designs available. I have used ideas from Kossel, Delta Pi, 3DR and, of course, Rostock. Many thanks to the designers of those machines for their brilliant ideas that I have shamelessly 'Cherry Picked' hence the name of my design!
The rods on my printer are 277mm from steel ball centre to centre. The towers are 800mm Bosch/Rexroth aluminium extrusion and the base frame extrusions are 250mm long as are, obviously, the top frame extrusions. You need nine in all.
The bearing carriers use 6 623 10mm x 4mm x 3mm bearings and slide directly on the extrusion. Nut traps for M3 nuts are included in the carrier. The rods connect to the carrier with a plate that fastens with 3 M3 bolts, again nut traps are included. The rod carriers and the effector plate hold 10mm x 5mm countersunk, cylindrical rare earth magnets and my rod end balls are 8mm diameter. My rods are 5mm carbon tube but you could use 6mm aluminium. My rod end balls have a 10mm M5 threaded rod and are the type used for the ends of gas struts, etc. the idea of the seperate rod carriers was to enable different rod attachment methods but the magnets and balls have worked out fine for me.