This is how the arrow rests on the spinner if I am checking for wobble. The end board that the tip is pointing at is what I call the wobble board If I'm cresting I put the nock end towards the end board. (Tip when checking for wobble check both ends against the wobble board)

The base is 24" long but if I had it to do over again I'd make it an inch or two longer than the arrows I plan to build. That way I could seperate the supports a little more.

The support closest to the check for wobble end is 6" from the wobble checker board and is 4" tall.

The 2nd support is 18" from the wobble checker board and is 4" tall.
This is the end piece aka wobble checker board. I made it 7" tall.

This is how I spin to check for wobble and or cresting. I place the palm of my hand here and stroke it back to get the arrow shaft to spin. Also note the square of metal on the base. I check for wobble on the spinner and back that up by placing the tip on the plate and spinning the arrow like a top. If it passes the wobble board and the plate it is good to go.

The marbles glued on top of the supports are about an inch in diameter but that's just a guess. The space between the marbles is centered on the top of the support board. I used hot melt to secure the marbles in place.
The paint is a waterbased paint bought from wallyworld. Since it is waterbased I sealed over it and the entire shaft with 2 coats of polyurathane.
Items needed to build the spinner/crester are:
1"x4" board about 6' long
hot melt glue
4 marbles
nails or screws
metal plate optional (ceramic tile might even be better since it would be smoother)