This is an x carriage for Mendel and compatible printers that use a 50mm horizontal rod spacing and LM8UU bearings or equivalent bushings.
It is designed to use M4 hex head bolts and the aluminium mounting plates available from hotends.com for j heads from the same source.
It is pretty much the same size as a standard carriage and thus is designed as a drop-in replacement.
I have tried to make the design flexible and work with easily available hardware:
Any belt clamp with m3/m4 holes and 10mm spacing that fits your belt will work.
No belt clamps are included, it is assumed you are upgrading from the commonly used Greg's carriage or similar: http://www.thingiverse.com/thing:9869
It can be used as a bowden carriage with your favourite adapter for that, as long it has 50mm spacing between the M4 bolts with the j head centred between them. See the included picture for one way of setting this up.
I use a customized output from this openscad design to fit my setup:
Basically you want to modify the script so that bolt_distance=50 and then change the nut size (hexSize=7 for M4 nut, in the coupling module) to match whatever you are threading onto the PTFE tube.
It can be used with any compact direct drive extruder as long as it is designed to fit over a j head, and again has 50mm spacing between bolt holes with the j head centred. A pair of these that I modified to fit over top of a j head with the aluminum plate can be used: http://www.thingiverse.com/thing:147133
Provision is provided on the carriage for a single 40mm fan at the back, between the belt mounts. This serves to assist cooling the cold-end and the printed plastic. It may also cool the hotend a bit, but it seems to work OK without a duct. I am working on designing a more specialized version with specific ducting. There are nut traps and holes for M3 nuts/bolts for fan attachment. The spacing is wide enough you can also use a 50mm fan with an adapter such as this: http://www.thingiverse.com/thing:47146
Attaching a bowden extruder and choosing the lengths of M4 bolts is left as an exercise to the end user, configurations can and do vary - consider this an open platform for adapting your current setup or available hardware to a dual extrusion system.
Rides on four bearings attached with zip-ties. Install all of the bolts from the bottom first, before installing the bearings.
Use strips of paper or kapton tape between the carriage and the mount plate to level the hot ends.