Wooden RA2 Backstop for tumblers.
Open File and set power settings to 100 and speed to 12
I used 3mm Walnut Plywood, but you can use whatever you have… 5mm would fit with out using the back plate (Smaller of the two cirlces)
Remove cutouts from machine, and remove the arms from the chuck. Place smaller circle on the chuck first, then the larger one. The larger one is cut so the rails of the arms are able to slide more freely. Attach Arms and test it out.