I've got a problem and I'm not sure how to proceed. I'm working on the VS rear spar and the plans call for dimpling the rear spar and countersinking the doubler. It's a #30 hole for an AN426AD4 rivet.
Before I do something irreversible to my doubler, I decided to do some fit checks on scrap. I cut a small coupon out of 0.032 in. material, which is the same thickness as the rear spar, and did some test countersinks on a thick piece.
Here's a picture: https://ibb.co/fojrnw
So the problem I'm seeing is that the dimple will not allow the sheet to lay flat against the countersunk part. I tried several different depths of countersink to get it flat, but when the sheet does lay flat the dimple will wiggle from side to side.
I measured the size of the dimple and it came out to about 0.350 in. I then countersunk another hole to 0.360 in. C/S diameter and it still didn't fit perfectly flat, however it was closer. There was still a gap between the sheets, but no wiggle though.
The dimple set is a 426-4 from Cleaveland Tools and the C/S bit is a #30 100 degree also from Cleaveland.
So to my questions:
(1) Is there a recommended diameter countersink for AD3 and AD4 rivets for a dimple resting in a countersink? Of course by diameter I mean the diameter of the C/S on the surface.
(2) What is the acceptable gap tolerance between parts?
RV-14A Kit#140433, N393AJ Reserved
Completed: Vertical Stab/Horizontal Stab
Working on: Empennage (Elevator)
Construction log - mykitlog.com/ajackson
Dues paid on 10 October 2018
Member of EAA Chapter 92
Pet peeve: "Lose" is the opposite of "find". "Loose" means "not tight".