Forward spar - Completed riveting of spar doubler. Attempted to rivet spar attach brackets:
This proved to be difficult and ultimately was a failure. The attach brackets are quite thick, as is the spar doubler, the total thickness requires a length 9 or 10 rivet. This is problematic as the pneumatic squeezer cannot handle this long of a rivet. Driving these rivets is also a problem and I did not have experience with very long rivets. The assembly was clamped securely to the bench, but execessive bouncing of the rivet set caused deformation of the heads as well as excessively deep "smileys" around the edges. I also noticed that the rivet work hardened before they were driven fully. I attempted to drill these out, this created execessively large holes. The result here is lessons learned and an expensive practice piece. The spar is 16 feet long and can only be send via freight, so I will be ordering it with the wing kit. After much research I found that there are tricks specific to these long rivets:
1. The rivet gun pressure must be turned up higher for these. I would typically use around 40-5 PSI at the gun for AN4 rivets. With the mass of the thick assembly this results in work hardening of the rivet from an excessive number of hits. This is very noticeable as the sound of the hits change as the rivet hardens. The pressure must be increased so that the shop head is fully formed in a reasonable amount of hits. I am not sure exactly yet what pressure will work best with my 3X gun. I will experiment before I get the replacement parts.
2. The higher pressure needed means more precautions must be taken to keep the set on the head. The use of masking tape over the head helps prevent slipping. It also helps to hold the gun directly in line with the driving force. I tried these techniques on my "practice spar" and the result is promising.
