OK, a couple of easy questions.

First off, I'm build ing some paneled doors and drawer fronts for a shop base cabinet project. The rail and stile bit set produces a panel slot that is 3/8" deep. So, my game plan was to cut the panel 1/4" smaller then the total inside slot measurement/s. This would leave an 1/8" gap all around for expansion. I'm using poplar.

1. Is 1/8 expansion gap enough?

2. The space balls I have are 1/4" in size, so I won't be using those. How do you keep the panel centered without using some type of material in the slot?