Dimpling the skin.
The back riveting technique is an easy way to get high quality flush rivets quickly. The down side is that you have to be able to access the back side of the piece with the rivet gun. Back riveting is used on the rudder and elevators and I also plan on using it on the top wing skins.
To back rivet you use a special rivet set and put the gun on the tail of the rivet. Riveters tape holds the rivets in place until riveted. Underneath the work piece I have a large, heavy steel back rivet plate that the front or flush side of the rivet and work piece rests on.
Back rivet plate and riveters tape, ready to flip the skin over and rivet. 
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