With the abutments bolted just hand-tight, we can overlay some 1.50 millimetre sheet and rivet it to the rotor-arms to fix the geometry. I've used leftover material, and in fact this is its third outing... another advantage of alloys over exotics. What this means here however is that it is slightly undersized at 12" square instead of 12.5", although we can live with this as it'll be in the museum at Oshkosh one day, warts and all.
Using 12 x 4 mm pop-rivets, fix a couple into each side of the square before loosening the bolts again prior to drilling the corners. During the great pandemic lockdown of 2020 I bust a drill-bit by not removing those bolts first. What, with all those hardware stores closed, "Fuck," I said.
