Timing belt instead of rack!

[BillTodd]

I realise that simplicity and accuracy dont go hand in hand.
Mind you ball screws are just not cheap enough.

Have a look at roller nuts:

http://www.cnczone.com/forums/showth...t=13593&page=2

This is a very long thread, but an interesting read with some good ideas for low cost alternative to ball-screws.

my original thought was to kill 2 birds with one chain so to speak in that the pulley running on the belt

If you could rig up some kind of positional feed-back (i.e. from a linear scale) then you could use a traction drive.