Weighing up re-rivetting - procedure and risks

My investigation of rivet behavior with dished and flat heads is making me lean towards a decision to re-rivet, at least selectively. Such a decision must factor in time, difficulty and risk of this operation, in damaging parts. If controlled, it is a great precaution against any lingering doubts about the performance of the dished rivets which will not be available when buried under many many more rivets.

My investigation of rivet performance has revealed how easy it is to remove rivets provided the correct procedures are followed. I have also noted the absence of hole expansion in 6061-T6 comparing before and after a rivet is set. It seems that the 5052 rivet alloy (AlMg2.5) does all the yielding. Done correctly I have found that rivet holes remain fully in spec after rivet removal.

Rivet holes are drilled to the following diameters

4.9mm for 4.8mm rivets

4.1mm for 4mm rivets

3.3mm for 3.2mm rivets

The requirements are that rivet holes should not exceed the above values by more than 0.1mm for correct operation of the Gesipa rivets.

An attempt at wholesale de-rivetting (low 100s rivets, at this stage) should not be considered if there is likely to be more than a small handful of holes to be enlarged or elongated beyond these levels due to mishaps (mostly drill centering errors).

In practice, in nearly all cases, the hole dimensions after deriveting are actually extremely close (+/-0.02mm) to the nominal diameters given above, well under the upper limits.

I have found that the risk of damage when deriveting is greatly reduced by the dishing of rivets, as currently set, since there is a slight gap between the bottom of the head and the metal surface. A visible depth margin currently exists when drilling out the head with the following procedures

The procedure for removing the rivets would be as follows:

4.8mm: drill almost to the surface level with a 3/16" drill. Insert the tail of this bit into the hole, and break off the head. Then drill down through the shaft of the rivet with a 4.1mm drill until the steel mandrel is reached. This weakens the shaft and makes tapping it it out much easier. Tap out the rivet shaft with a 4mm punch, with a bucking surface for support

4mm: drill almost to the surface level with a 5/32" drill. Insert the tail of this bit into the hole, and break off the head. Then if the rivet has an extended depth drill down through the shaft of the rivet with a 9/64" or 1/8" drill until the steel mandrel is reached. Tap out the rivet shaft with a 3mm punch, with a bucking surface for support

3.2mm: drill almost to the surface level with a 1/8" drill. Insert the tail of this bit into the hole, and break off the head. Tap out the rivet shaft with a 3mm punch, with a bucking surface for support

When done, the rivet holes are cleaned with Turps, of any wet Duralac, or dislodged primer. They are then checked dimensionally. If mishap has resulted in any elongation, etc, repair with JB-Weld if damage minor, or consider stepping to a larger rivet.

At present for the wing, only the flap, ailerion, wing ribs 1, 4, 8 and 9 are rivetted in several cases only partially due to waiting for parts. No skins have been rivetted.

The empennage internals have been mostly rivetted but again no skins, also due to waiting on parts. The number of rivets in the empennage internals to be possibly re-set comparable to the wings. There is also the greater difficulty and risk in de-rivetting the thinner materials in the empennage.

I imagine the overall task would take a couple of weeks.