Installing Backing Plates
Step 2: Fabricate the aluminum stock to be used for the backing plate. Use a rectangular piece of aluminum that’s 1/2 inch thick by 3/4 inch wide with a length that’s at least 1.5 inches greater than the maximum distance between the mounting holes. Use a marine grade alloy like 6061, which has some corrosion resistance. Then carefully drill and tap two holes for the alignment rods. These holes must match exactly two of the hardware-mounting holes. If the hardware has more than two mounting holes, the rest of them will be drilled and tapped once the backing plate is in place. Use the hardware itself as a template for locating the holes. Note that we’re making threaded holes for the alignment rods, not for the final mount. The edges of the aluminum plate that faces the inside of the mast should be rounded to conform to the inside curvature of the mast. Either a file or a belt sander can do the job easily.