I have been told by what I consider to be very reliable sources that both Vans and Synergy Air have tested drilled, deburred, dimpled, riveted joints versus simply dimpled and riveted and the non-deburred joints performed as well or better than the deburred. This is the way I am doing it.
Tim
I can reliably say that what you are saying is true
but you have left out an important detail.
Dimpling without final drilling and deburring on prepunched holes for kits prior to the RV-12 and RV-14 is not recommended because the holes are punched slightly under sized. This means that the dimple die pilot is bigger than the hole, so it must be forced through which stretches the material even before it begins to form the dimple.
Doing this on a prepunched hole that has not been final drilled (cleans up the rough surface finish of the material edge inside the hole edge), or deburred, adds a much higher risk of radial cracks at the perimeter of the holes.
Case in point...
On the RV-12 and RV-14, which the plans specify dimpling without final drilling or deburring, the holes are already punched correct size for the rivets and the dimple die pilots are a slip fit. But on these two kits, on any holes larger than .128 (for 1/8" rivets) the holes are punch under size and specified to be final drilled to proper size, and then carefully deburred if it is intended to be dimple countersunk. The reason for this is that the bigger the dimple, the bigger the amount of stretch that occurs in the material at the edge of the holes while the dimple is formed.
So, Van's does
not endorse (and we don't do it our selves) dimpling skins that have not been punched to final size, before they are final drilled and deburred (the deburring is because final drilling typically leaves more burr that the punching process does). This would mean that any kit other than the RV-12 and RV-14, the recommended procedure is to final drill before dimple countersinking.