I'm guilty of buying those inexpensive sanding blocks in the past. For the most part they work but I've often found that they either don't hold the sandpaper in place very will or they are extremely uncomfortable to use. We are talking about hand sanding after all. Why make it any worse on your hands than it needs to be. After cussing about the last small block sander I bought several years ago I decided I would be better off making a simple one myself.
3-2/3" x 9" sandpaper (the type used for electric sanders)
a scrap of 2"x4"
a staple gun
foam, rag or some other type of padding (wadded up duct tape will work too!)
Step 1: Cut the Block to Size.
Cut a 2-1/2" length off the 2x4. This will be the sanding block.
Step 2: Pad & Tape.
Set the foam, or whatever padding you have chosen on top of the block. Tear off several strips of duct tape about 3-4" in length and one at a time tape over the padding to the block sides. Do this until you have the padding thoroughly secured and decorated in a stylish silver that is duct tape.
Step 3: Secure the Sand Paper.
Fold and tear a piece of the sandpaper in half. Flip the block upside down, place the piece of sandpaper on top and fold each side so that it is fairly even. Now staple each side, securing the sandpaper to the block.
When you need to replace the sandpaper all you have to do is pull the staples or even staple a new piece directly on top of the old. I have found that the thickness of the 2x4 block combined with the foam padding is much more comfortable to use for finish sanding than any sanding block I have purchased. Best of all, it is cheap and takes only minutes to make.