Name: IMG_20170426_200503.jpg Date: 2017 Apr 26 Size: 0.89MB ---------------- Doubling up the ground ring 3_4" plywood (19mm) scrap glued & screwed together. The ring needs to be thick enough resist bending down. It must be at least as strong against bending "out" (trefoil-ish) Note: the inside edge relief of the SudiBall in the background where the tube will pass thru