thanks for the input guys , may bin the mdf idea seen aluminium herehttp://www.aluminium-profile.co.uk/a...10mm_Slot.html

could get a frame for about £60 ,would it crab with 2 bearings per rail spaced say 200mm , could i run two skate bearings against the outside of the frame on the non driven side to keep it parallel and stop the racking , i have aready ordered the 16mm rails from zapp