garageFab.cc

One of the expensive materials used in Contraptor set is Teflon angle. I had tried to find it cheaper than on Mcmaster.com, unsuccessfully - it is only available in one other place online, and it's even more expensive there, around $30/ft. Ultra High Molecular Weight Polyethylene (UHMWPE), which has coefficient of friction fairly close to that of PTFE, might be an inexpensive replacement. I ordered some UHMWPE to test out and built a couple of sliding elements. Turns out, the performance is as good if not better than with Teflon. 

There are couple of things that are different in making sliding elements with it though:

• UHMWPE is harder and needs more force to cut with a knife, so it must be done carefully.
• UHMWPE is abrasion resistant, so where the file was used to thin the overhangs before, hacksaw is needed now (Dremel cutter might also work).
• UHMWPE needs light deburring (with file) after drilling holes in it.
• The screws, holding in place the pair of overhanging pads, should not be screwed in all the way. There should be a small gap between the screw head and the sliding element, otherwise the pads fall out when the rail is not in the sliding element. 
• I think the abrasion resistance is also the reason why UHMWPE pads are sensitive to drilling burrs on the angle rail - something that was not as much of a problem with PTFE pads. There are two ways to deal with it - either thoroughly deburr the rails (file/sandpaper), or make shallow indentations in the pads, where the holes slide. The latter is somewhat time-consuming using a hacksaw, however it might be faster with Dremel.

The best part is that UHMWPE costs only a tenth of Teflon - $2.8/ft. In addition, it's in channel form, so the material usage for corner angles of the sliding elements is more efficient. I did the math - if I end up having to switch to more expensive higher torque motors, UHMWPE instead of PTFE will effectively neutralize the associated cost increase (+$16*3 axes).

The black screws seen in the pics are the Nylon screws that I'm trying out instead of the steel screws for some components. This is so I can cut them with a knife and not a hacksaw - faster and not messy.