Dimpling the rudder ribs (and other control surfaces) will be a challenge but with a little creativity, it can be done without relieving the bends dimpling then re-bending the ribs which I feel is the wrong path to go down.
Earlier today I took the time to work through a small issue that I knew was going to arise at this point in the construction … because of my decision to dimple the parts for flush rivets. I remembered from working
on Pete’s RV-9A that the last couple of rivets on the trailing edges of the control
surfaces can be tough to get at for dimpling. I think the RV-12 is even tighter
yet. The last two holes on both sides of the narrow end of the rudder ribs will
require special treatment … because there is no room for the usual methods of
dimpling. Even while work was been done on other items there was a lot of
thinking going into what sort of jig or tool would work to dimple the small end
of the ribs that make up the control surfaces. Using scrap metal, my first easy
idea of squeezing the dies together with a small vice grip (no room for a
regular vice grip) did not work well … was not able to get achieve enough
pressure to get a deep enough dimple for a flush rivet to sit flat … scratch
My second idea (which was actually my first but
required grinding metal off a tool so it became my second choice) turned out to be
the best overall. A small 1/8” nail was cut in length to go through the 120
degree dies I had custom made with holes in them. The length of the nail was
made just shy of the total depth of the dies when placed together. The purpose
of the nail is to keep the two dies centered on the hole being dimpled when they are squeezed by a C-clamp.
The C-clamp needed a portion of the
back of the clamp ground away on a grinder to allow for clearance at
the very narrow space available due to the taper of the rudder ribs.
Fortunately, Van’s offset the two rivet holes at the narrowest point on the
rudder ribs … because of this nicety, the dimples at the narrow end of the ribs
won’t create a clearance issue and interfere with one another after dimpling. That said, should you decide to build your RV-12 with
flush rivets, I would strongly suggest dimpling the hole with the least amount
of clearance first.
My crude but effective way of generating enough
brute force to dimple the ribs.
The short nail stub keeps the dies aligned with
the hole while the C-clamp squeezes the dies together.
Clicking on the photo above to make it larger
you can see the first dimple I made by placing a nail into the dies to hold
alignment, then squeezed the dies together with a C-clamp. The C-clamp had
material ground out of the back side to gain enough clearance to fit into the
small opening at the narrow end of the rib.