When you turn calls on a mandrel you can't rely on wood or your drill press being square. After you drill your holes you have to square both sides of your blank to the hole you drilled or you will have some wobble.
If your boards were plained perfectly flat one side and your drill press drilled at a perfect 90 degs to the table it would be much easier to turn a call that didn't wobble when you turned it over.
I start by drilling all of my holes on the drill press. By drilling all of the sound holes the same depth it makes it easier to get a consistant thickness on the bottom of the call.
After drilling the holes I clean up any tear out on the hole that goes all the way through with a piece of sand paper.
With the tear out gone the pot will lay flat against the spacer I made for my mandrel.
This is what my spacer looks like. Its made from scrap that I had laying around the shop.
When I put the call on the mandrel I put it on so the side with the sound holes faces out and the side I cleaned up the tear out on is facing the spacer.
Next I clean up the bottom of the call and square it to the mandrel. If your going to put any divots on the bottom of the call now is the best time to do it. I try to do everything to the bottom of the call that I want to (except sanding) before I hollow out the inside.
Now it's time to flip the call around. It's going to wobble until you square it up.
After both sides are square I shape the outside of the call and then hollow out the center. I use a 3/4" center hole and the center hole is part of the sound board pedestal.
This method isn't perfect but I can flip the call around and get very little wobble. I did a test. I flipped the call back over and marked four lines on the call and made 2 light passes with a scraper.
It's not perfect but it's
close. You can see a little bit of the 1 line at 10 o'clock but the rest of the lines are gone.
