igus bearings are cheap ,can be used on aluminium shafts , itwould seem to me, to be a no brainer ,am i missing something?I dont work for them but have used them in projects.self-aligning maintenance-free spherical bearings made of high-performance polymers link:-
[www.igus.co.uk]

they have plain bearings as well, or more fun:-

[www.igus.co.uk]

hope this helps someone

Hey, neat, some of those are probably printable, once we get our resolution up a bit.

My first 2 RepRaps used plastic bushings everywhere, but they do tend to wear out over time - I've got about 50 km of head travel on one of the machines now. That's one of the great things about the Mendel - if there's any wear over time, (and there should be little with ball bearings and steel rods), it's very easy to tighten up the bearings.

Properly manufactured bearings like those might last longer though, but then it's tricky to avoid the over-constraint problem on all 3 axis.

Wade

Another great thing about igus bearings is that you can calculate the wear over time using the easy on-line expert systems. The wear is usually measured in microns per kilometre, not is not usually an issue. Also, igus do make a series of adjustable bearings, so any clearance could be taken up anyway.

Wade has a good point about over-constraint, but usually 2 shafts are used in parallel, in which case one shaft should be the "master" or "fixed" and the other the "slave" or "floating". The whole system is kept accurate and stable by the fixed standard bearings, and self aligning bushes can be fitted to the floating shaft, this eliminates any possibility of over constraint.