Brief Description: Left tank: install floating nutplates (Part I)
Long time, no airplane work! Spent a while (not logged) cleaning up the shop, the some time (logged) scratching my head over the left tank.
Floating nutplates MS21059L3 from GAHCo are still backordered. Found MS21075L3N at ACS--for cheaper than GAHCo. (See Image 1.) How to deal with 0.312" spacing of the rivet holes? (Standard nutplate spacing 0.688").
Finally ecided to "fill in" the existing csk rivet holes by cutting AN426-3-3 rivets down to "AN426-3-1" size. Drilled a #40 hole in a maple block and csk for flush rivet. Made a cut ~1/8" from edge. Placed a rivet in the csk hole, held it in w/a scrap of wood (Image 2). The scrap of wood is important--the rivet head gets very hot in a hurry as the shank goes through the blade. (Don't ask me how I know...)
