This is what I have choosen for my Sonex project. I don't reget this decision, but recently ran in a big mess.

The Problem

The problem seems is connected to my dimpling practice (or the tool?). Some time ago I purchased some of the highly praised 'Avery' springback dimpling dies. When I drill for AD-4 rivets, I use a #30 (or #31, makes not much difference) drill bit. Then I dimple. The hole will expand by this dimpling process to about 3.6mm (metric from here on). This is too much for a 1/8" rivet (according to AC43-13 and good judgement). I made some tests and it's obvious that the rivet does not fill up completely this oversized holes. The joint is sloppy.

Panic Reaction

I have contacted Avery's tech support by email two times but did not receive any response yet. Also the Internnet had no good advice. What makes the mess worse is that I have already dimpled both rear fuse sidewalls and the attaching bulkheads (sevaral 100 rivet locations). If this sidewalls are scrap then also the longerons are, the bulkheads and more than 100 hours of building. This work I definitely won't repeat. If the parts cannot be saved then this project will join the other 80% of unfinished hombeuild projects (gladly I didn't order an engine yet).

The Cure?

I dimpled and opened up some holes for AD 5 rivets. These are the 'big' (4mm) ones used to rivet the wing mainspar. Totally unsuitable (unesthetic) for fastening thin skins. The sides look like sh.. now. Maybe I can get used to it - I don't know.

Future Dimpling

This guiding stub at the male dimpling die I have grounded down to about 2.5mm diameter. This way I can dimple directly the pilot holes The dimpling will widen the hole almost perfectly to 3.2mm. Disadvantage is that small misalignments of the pilot holes cannot be corrected anymore.

If someone who may reads this and has a (better) idea what to do, please let me know