My piece of maple was about 1 1/4" by 1 1/4" by 12". Clappers are generally about 2" to 3" wide, but I decided to use my skinny piece for now and make a larger one later. I drew a half circle at both ends to mark where I was going to round it off.
Step 1: Cut Rounded Edge With Band Saw
Step 2: Sanding and Finishing
After the belt sander I used sand paper to further smooth the surfaces, progressively working down to finer grits. The last paper I used was 400 grit and gave the clapper a wonderfully glassy smooth finish. I also turned the clapper on edge 45 degrees and sanded down the sharp edges just a touch. This ensures that the edge of the clapper won't press an unwanted line in my fabric.
That's it! You don't need to seal, stain or varnish the clapper, as those things could potentially transfer to your fabric. Just shape it, then sand it till it's mirror smooth!