Prepared edges of R-901 skins, R-913 counterbalance skin and rudder ribs. Deburred and dimpled skins and ribs. Set countersink cage for #40 holes on R-916 trailing edge extrusion.
Dimpling the last 3-4 holes at the narrow end of the R-903 and R-904 rudder ribs is very tricky. Even the pop-rivet dimple dies are no use as there is not enough separation between the flanges to get the long nail that pulls the dies together into the holes. I looked on Doug Reeves Vansairforce forums and found various approaches. One is to drill and countersink a piece of mild steel and use it as the female die to make the dimple. Another builder had adapted his DRDT2 dimpler as pictured here. While machine countersinking the hole in the steel with the bench drill and the #40 countersink cutter mounted in the hex adapter (that I usually use for my deburring bit), I managed to break the pilot off the countersink cutter. This was because the steel piece was not held securely and the pilot jammed in the hole when it came up off the table and the hole being countersunk moved out of the vertical plane. That will mean that I can't countersink the R-916 rudder trailing edge until I replace the countersink cutter (or borrow one temporarily from someone else).
I got down to the last two holes on each rib using the pop-rivet dimple dies and I tried using the mild steel die on the final holes with the normal male #40 dimple and a light hammer. However, I am not happy with the results. The test rivet did not sit properly into the hole. This is probably because the countersink cutter did not do its job properly before I thrashed it.The final solution I came across was from Dan Checkoway, whose own website is legendary. He says
simply bend the flanges out until you can get at them and then bend them back again. However, I wonder if the metal will be work-hardened by this process. In the end, I decided to partly follow Dan's advice. I gently parted the two flanges until I could just get the female pop-rivet die and nail into the last hole. The flange sprang partly back into position once the nail was in, leaving only a small 'permanent' deflection from its normal position. Once the dimple was made, I had to spring the flange slightly further out of position to get the nail head back out. However, after all the dimples were made, I was easily able to get the flanges back to square using the flanging tool. this picture shows a test rivet sitting in the last hole of the R-903.
simply bend the flanges out until you can get at them and then bend them back again. However, I wonder if the metal will be work-hardened by this process. In the end, I decided to partly follow Dan's advice. I gently parted the two flanges until I could just get the female pop-rivet die and nail into the last hole. The flange sprang partly back into position once the nail was in, leaving only a small 'permanent' deflection from its normal position. Once the dimple was made, I had to spring the flange slightly further out of position to get the nail head back out. However, after all the dimples were made, I was easily able to get the flanges back to square using the flanging tool. this picture shows a test rivet sitting in the last hole of the R-903.
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