I decided to use some self-etching primer for the stiffener/skin union for the rudder. Making up a batch of 2-pack primer was going to see most of it thrown away. I plan to spray 2-pack primer over the whole lot when I finish fabricating, drilling and dimpling the rest of the rudder components so I can spray them all in one go.
After spraying some primer down the rivet hole lines on the skins and on the skin side of the stiffener angles, I let them dry and then clecoed them to the skins. I then picked some -3-3 flush rivets and popped them in the holes, holding them in place with some rivet tape. Next the skins were flipped over and I got my back riveting set and plate ready.
I would like to warn others at this stage to be very careful that the back plate is properly aligned with the rivets. I had 2 instances where I didn’t (1 on each skin). In the first instance, the plate’s edge was right through the middle of the factory head when I tried to set it. This almost split the rivet and it deformed the dimple in the skin and stiffener. I managed to drill this rivet out without enlarging the hole and ended up re-dimpling the hole with my C-frame. This is what the deformed dimple looked like after I drilled out the rivet.
The second instance was me just getting complacent. Things were gong smoothly and I was probably going a bit too quick. Consequently, I ended up trying to set a rivet with the back plate edge running across the edge of the rivet hole (i.e. in a tangent). This created a small crease (for want of a better word). I drilled out the rivet and de-dimpled the hole. This is what it looked like after I dimpled it.
The crease is not full thickness, and it is fairly small. I replaced the rivet and set it without any dramas. I’ll get my TC to have a look at it at his next visit to make sure it is OK.