I wanted to pass this along. I made two sets of coasters with team logos. I made these out of shorter material, so I used rails on the sides to meet the 7 inch rule.

The first set was made from 1/2" thick material. Although I didn't notice it until spraying with urethane, but there is a gradual ridge which I attributed to the point where the leading edge of the board got under the forward roller.

The second set was made from 5/8" material, and there is no ridge.

Apparently, there is just enough flex in the thinner board that it must be raised up a little when the board is not under the roller. The thicker material must be a bit more rigid and does not seem to have this problem.

Just something to keep in mind.