The trailing edge of the rudder has a very thin wedge of AEX sandwiched between the left and right skins. This fragile piece of metal has to be well secured during the countersink operation making ready for the double-sided rivets eventually holding everything together. Using the angle iron jig prepared earlier, I drilled #40 holes through the iron about every 7th hole using the AEX piece as a template. Clecoes were then used to clamp down the trailing edge for processing with a micro-stop countersink.
The two middle holes indicated with the Sharpie lines in the middle are #30 in size – big enough to allow the guide portion of the countersink bit to protrude through the trailing edge, but small enough to still provide solid backing. The overall result was very good. A few finished holes can be seen on the right.