[Michael C Henry]

If you are fitting percesice holes go under sized and open while smoothing .For me hole saws have always cut a larger hole than the size measured distance accross the hole saw . The tape and sand paper are winning tricks.
If you want to make a simple tool that you can use in different jobs mostly inside objects. Get a piece of rigid strait drill rod. The length will depend on how far you need to reach into your work. Put two hacksaw blades in a hacksaw frame from the end saw a centered two inch slot .Now insert two inch sanding tape into the slot and twist in the direction that your drill motor would. The amount of sanding tape would determine the size of the roll,and and coarseness of sanding tape would varry. Use coarse for stuff like heavy rust and fine for smooth finnish. You can add lengths by inserting under a flap of tape allready wound tape. You can tear off tape as it is worn out or filled up. and twisting. I have many different lenght of drill rod for different reaches. With the longer lengths you can put side pressure with your hand on the shaft above the sanding tape . Mine are callased but a cloth glove would work also.