Two years ago, I built a jig to help me cut sandpaper sheets into a few different practical sizes for our classroom. The sizes that we use are eighths, quarters (long strips) and half sheets.
The eighths pieces are very useful for hand sanding and for working small to medium sized projects. We mount the long quarter sheet on our beloved Preppin sanding blocks, and the half sheet is useful when I sharpen gouges and chisels.
Begin building the jig by drawing a rectangle the size of half a sheet in the middle of a piece of plywood. Then I divide the rectangle in half to outline the long quarter sheet strips. I drew another subdivision to outline a traditional quarter sheet rectangle, shown in red. This size also helped me complete the cuts of the eighth sheet segment (see below) and cut traditional quarter sheet sizes.
To cut the paper, I use a hacksaw blade that is screwed onto the jig, with the teeth facing towards the cutting field. You can adjust the height of the saw blade to match the thickness of your sandpaper by placing a thin shim made of cardboard underneath the holes – or you can leave one screw a bit loose, which will allow you to lift the saw blade before tucking the paper underneath. Either way, make sure that your screw shank equals the hole diameter.
Last word of advice: when cutting, place the sandpaper upside down and apply firm pressure on the blade as you rip the paper up.