I'm getting really close to being at a stopping point until I get more primer. The pile of parts to be primed is getting pretty deep! I took a quick break from the firewall to figure out the pitch autopilot servo bracket that got delivered recently. The only measurement they provide is the distance of the front flange of the bracket to the center of the bellcrank pivot point. How the bracket is attached to the bellcrank rib is left up to the imagination of the builder. They simply say it can be bolted or riveted to the rib. Since I had left three holes open in the rib, I decided to just go the rivet route. The bracket comes with a bottom flange that can be riveted to the skin. They say it can be cut off though, so instead of drilling more holes in the skin, I decided to remove the flange and just rivet the bracket to the rib. I match drilled to the top three rivet holes in the rib/angle, then drilled another two rows of three rivets. This bracket is all I need to install for now (after I prime it...it's in the pile). The servo and connection to the elevator bellcrank can be done later.
Back to the firewall. I needed to deburr the holes, but the stainless steel was far more difficult to deburr than aluminum. I tried a cone shaped grinding stone in the die grinder, but the holes just ate it up. Then I tried a drill bit, but it wouldn't cleanly trim the burrs. I asked online and the suggestion was to use a cutoff wheel at really low speed. That did the trick.
Next up, dimpling. All of the rivets used on the firewall are flat head rivets with the manufactured head on the front side. This makes the firewall smooth on the engine side so mounting brackets is easier. The stainless is very easy to dimple since it's super thin, but it dings and deforms much more easily than aluminum sheet.
Since the firewall gets dimpled, that means all of the brackets, spacers and stiffeners have to be countersunk. I got about halfway through with them before stopping for the day.
