The problem (danger) with text discussions like this (no one on one, physical demonstration) is that light deburring can mean very different things to different people. Especially if they are a novice at aircraft construction or working with very thin sheet metal.
A recent post mentioned using an electric screw diver and only turning the bit one revolution. That is probably ok if done properly. Anything more than very light pressure on and the skins could be being turned into scrap without knowing it (considering that with the tool doing the turning, the operator has no torque feedback based on how much pressure they apply) .
The shear strength of a riveted joint is related to many factors (rivet strength, material strength, etc), but for a typical RV builder, they have no control/effect on most of these (it is inherent to the design). Where they do have control is in what they do for deburring. An undeburred hole on an RV-12 skin is not likely to have any strength difference compared to a properly deburred one. The burr is (usually) very small and its sharp edge is aimed away from the skin surface and does not actually bare on the rivet shank directly. If instead of doing nothing, the builder over deburrs both sides of a skin, they are actually reducing the cross section baring area within the hole. This causes two problems. With the load of the rivet working against a reduced baring area, the skin material can have a tenancy to yield at a lower load value than it would have otherwise. The other issue is that you have now made the surface area inside the hole more like a knife edge which can result in it more easily cutting/shearing through the rivet.
Years of experience has shown that RV builders (particularly beginners) tend to deburr excessively, to the point it may actually be weakening a rivet joint (see causes above).
This needs to be taken into consideration even more with an RV-12.
Why, you ask?
Because the skins are thinner than the other RV models. In some cases only half as thick. This leaves very little tolerance for error when deburring RV-12 skins.
This is the reason that emphasis was put on deburring holes made in the traditional way (a drill bit generally leaves a pretty jagged burr that would interfere with flush fit of a mating skin, etc.), but the burr typically left by the punching process is not much of a factor. There are exceptions... (sometimes a tool has started to get dull) so inspecting is a good idea, but anything that does not seem like much to a bare finger slid over it, is probably fine. Once again... describing versus showing is a difficult situation.
Bottom line.... deburring incorrectly can be far more detrimental than not doing it at all. Particularly on an RV-12.
If you are doing it, make sure you know that you are doing it correctly, and not just feeling secure in the fact that "you are building your airplane the right way.... deburring every single hole"
(I have encounter a lot of instances over the years where a builder in full confidence New they were doing something properly, but the weren't even close)
