I needed to make a jig for using a router to mill large slabs flat on both sides. The slabs are too large for a planner or a drum sander. If the slab was not close to square, a belt sander would not be able to cut enough off. So instead of spending $1000 for a jig, I am building one with the help of these Linear Rails with the ball bearing slides. I actually bought 2 sets of the rails, 1 set is 60 inches and the this set (40 inches). The longer rails will be mounted on a side that is parralell to the slab on each side for the jig to rest on and be able to move it from one end to the other and the shorter rails will attach to the bearings of the longer rails an the router will sit on a platform attached to the bearings of the shorter rail. This allows for the router to be moved easily across the slab and from one end to the other and hold the router flattening bit at the same level.
Ray Richardson 
