I barely got anything done tonight due a new issue… cracking on the shop heads of the AN470 4-5 rivets.
The very first rivet I set, completely cracked, and didn’t even form a proper head. I was perplexed because I knew I had squeezed it properly. No worries, it was an excellent opportunity to use my new rivet removal tool! I was able to set the proper drilling distance on my second adjustment, and the rivet head snapped off perfectly. Certainly the easiest and best job I’ve ever done drilling out a rivet… so we’ll add that to my list of awesome tools.
I continued to rivet the rudder spar and spar reinforcement plates. On the third plate I noticed another crack. The crack was diagonal just like the first one, but not as severe as the head was properly formed. I decided to inspect all the rivets I had just set. Turns out about 8 of them show some type of cracking. Time to stop and give some consideration to the problem.
I found some information on Van’s Airforce. First this thread shows the EXACT problem I have. Same rivet type, and same angular cracks. I also referenced the mil-spec for the problem which states that “Cracks in driven heads (1) which fall with a circle concentric to 1.10 times the diameter of the nominal shank diameter, or (2) intersecting cracks, or (3) five or more cracks” are unacceptable. Finally, I found this thread which provides some feedback given by Van’s support. The majority of the time Van’s recommends leaving the rivet in place.
Its really hard to tell, even with a magnifying glass if the rivets are within spec. There are a few that look worse than others, and I will likely drill them out. More to follow.