I followed the supplemental plans for the most part except for the initial locating process. I did measure from the center of the hole they called out. And I drew a perpendicular line on the rib flange along which the crotch strap parts will line up. But what is important here is how these two parts fit relative to the hole cut out in the seat skin.
So I drew a centerline on the flange of the aft crotch strap plate. The flange is about .6 wide, so this line is about .3 from the edge.
Next I clecoed the floor skin to the ribs. Then I clamped to the two crotch strap parts together with the 1/8 spacer in between and positioned them inbetween the ribs and slid them up to the skin. I wanted these to fit flush with the skin.
I moved the two crotch strap parts until the center line showed through the two factory drilled holes. I clamped and drilled these to holes. Then I drilled the other two holes thru the floor skin into the flange of the crotch strap part. This positions the crotch strap flush with the skin and centered in the rectangle hole.
