When I need a circular workpiece for a project, I don't try to get it perfect the first time. Instead, I start by cutting the workpiece to rough shape. Then to make quick work of sanding the edges smooth (and getting the disk perfectly round), I use a simple sanding jig and a disk sander, as shown in the photo at right.
Jig: Basically, the jig consists of three parts: an MDF base, an adjustable hardwood runner, and a pivot pin made from a dowel (Figure 1). The runner slides in a groove cut in the base. This way, you can adjust the position of the pivot pin for different size disks. The work-piece fits over the pivot pin that's glued into a hole in the runner.
Note: The pivot pin can be any size you need. I have a set of runners with different size pivot pins. But depending on the dowels you use, you may find the fit a little loose. A quick way to solve this problem is to wrap the pivot pin with masking tape until you get a snug fit.
Setup: Using the sanding jig couldn't be much simpler. Start by clamping the base of the jig 1/16" from the face of the disk sander and just to the left of the center, as shown in Figure 1.
Sand Disk: Then just fit the workpiece over the pivot pin and slide the runner forward until the edge contacts the workpiece. At this point, all that's left to do is clamp the runner in place and sand the disk by rotating it clockwise (Figure 2).
Nice!
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