While I had presented instructions for a disk sander elsewhere, there were some questions raised for a 3" disk and for those who do not as yet own a Jacob's chuck but have a drill press or an electric drill that can be mounted in a bench vise. So...
Woodturning sander for you to make. Page (1)
An alternate method of making a disk sander for the electric drill for woodturning, especially bowls and vases.
Take a piece of 3/4" plywood and draw around a 3" sanding disk with your choice of pencil or what have you.
Cut the disk free on a bandsaw. A jig saw will do although it takes longer.
Drill a 1/4" through hole on center.
Using a 3/4" spade bit drill 1/2" deep into the wood. the point of the spade bit will serve to center the bit. the depth will allow a washer and nut to be countersunk into the disk.
I do not like to hold threaded rod with a drill so I start with a 1/4" bolt, 2 1/2" long; 2 nuts and 2 washers. If you do not mind holding threads in your drill chuck, threaded rod may be used or a carriage bolt or what have you.
I cut the head off the bolt with a hacksaw. I now have a 1/4" piece of steel threaded 1/4"x 20 on one end.
Save yourself feeling foolish. Put a nut and washer on now!
Assemble nut, washer, wood disk, washer, nut and tighten.