my plan is to build router that can take 8x4 sheets so the belts would run full length of table crossing over gantry to other side,both being driven by toothed gear reduced down from stepper motor then the back of the belts would go round idler then down the other side of router. Hope that kind of makes sense:confused:
I wish i could just draw a bit faster and better but am just learning autocad
Understood perfectly. Have you priced it up tho? as Irving said belts arnt that cheap espesially as you'll need them 12' or more in one run as it also goes thro the Y axis.

I think that once you get to 8'x4' belts arnt a cheap option, just cheaper than ball screws

I wouldnt have thought belt sagg would be to much of a problem as they will be on their side, and if you use collar less pulleys you could put a small ledge for the belt to sit on.

If you make our own Vee bearing will you save that much? Have a word with vic66, hes using vee bearings and angle, look at his thread and theres a link to the mechmate stuff which sounds simillar to what you want.