Remodelled to suit my build. The biggest problems I had with the original design were the clamp cracking through the thin section, and the printed bushes being very sloppy. The original design was passable, but it was made much worse by the poor print quality of my first set of parts.

• Bushing replaced by Xlube S48M 8 x 12 x 12 hatted bush http://www.mulfordengineering.com/pdfs/MEP-Finished_Products_brochure.pdf
• Takes an M4 captive nut
• Shape simplified and material added to strengthen the part

Printed on a Replicator 2X, 0.2mm layer height, 3 shells and 50% infill. Support is required.
Takes 2 hours and 22g of ABS to print a pair (so 4 hours for a full set).

You could probably print them with thicker layers and less infill but I prefer strong, high quality parts at the expense of more time in the printer.

I think it should be printed with the largest flat face against the bed, this means the 12mm bore is not 100% round due to the layers, but that should be ok as there is a proper bush being pushed in. I had to run a 12mm drill bit through by hand just to clean up the remains of the support material, but after this the bushes press in nicely.

The main reason for this orientation is to make the layers run perpendicular to the clamp so it cant snap or delaminate when done up tight.

On my printer the clamp bores came out a little undersize, I considered adjusting the model, but I think its better to have them under size than over. Its easy enough to remove a little bit of material with a drill bit if they are too tight. I just stretched mine over the 8mm shafts and it seems to work well.

On receiving my Xlube bushes I found them to be quite loose on the shaft. I think they are meant to be pressed into a metal housing and there is room for them to 'crush' down a little and still be on size. I am going to try them out for now and see how they go. I might look for a better alternative in the future.