Hi C Cunningham,

As Mark points out I am running bearing races directly onto Ali profile, but I always knew it was a short term solution and a small witness mark is appearing on the profile where the bearing runs over it. Not the best long term solution, although a hardened running strip might give better service.

Stray dust and chippings do get engrained on the top ali surface, and aligning the whole gantry (90 deg to bed, same height from bed at each each etc) took some fiddling. Once the extractor shoe is working that should solve the dust problem. The top and bottom bearings are fitted to short axles which run in adjustable slots in the side pieces. This allows complete alignment adjustment vertically. Side to side location is from single bearings set into holders, with one side fixed and the other side on an adjustable pressure plate. A bit like these :

http://www.axminster.co.uk/axminster...all-prod21223/

Linear motion, cnc and cheap are a difficult combination.