I have a small, benchtop belt and disk sander. It works great, but sanding a square edge on a workpiece is difficult. To remedy this problem, I built the sander fence you see here. It’s simple, accurate, and the fence can be adjusted for even wear on the belt.
The jig is made entirely of plywood. The drawings below show you how it goes together. NOTE: You may have to adjust some dimensions to fit your sander. You can see in the drawing that the base has two dadoes and slot for the sliding fence assembly. The uprights slide in the dadoes to adjust the fence.
The uprights are held together at the bottom by an adjustment plate. A hole in the plate is for the adjustment bolt and knob. The fence is attached to the uprights with a few screws. Here I took some extra care to make sure it was square to the belt all along its length. (You might have to use shims to square it up.) Now, sanding a square edge on a workpiece isn't such a challenge.