Can I avoid machine countersinking this thin part?

[DonMcKee]

I'm prepping parts for the W-00012 ADAHRS Mount Assembly to be used in my RV-14A wing:



The instruction to machine countersink the 0.032" thick W-00012C Retainer for an AD4 rivet made me pause. I considered machine countersinking the underlying, and much thicker, W-00012B Mounting Spacer, and dimpling the Retainer, but then it dawned on me: why not use 470AN4 universal rivets instead of the 426AN4 flush rivets called out in the plans?

There wouldn't be any interference with the GMU-22 Magnetometer that I plan to put there:



and, as far as I can tell, there wouldn't be any interference with the Dynon SV-ADAHRS-200 unit that was originally meant to go here, either. There may have been a good reason to use flush head rivets on the W-00012C Retainer, but I don't see it. Do you know what that reason was, or why using universal head rivets here would be a Bad Idea?

 

[Mel]

You should not machine countersink .032 for a #4 rivet. Unless I'm missing something, I agree with your assessment of countersinking the 00012B and dimpling the 00012C. I would not use a universal head rivet just in case there might be something come up later.

Murphy's Law says, "If you use a universal head rivet here, a flush surface will be required at some point!"

 

[Mark Dickens]

I have learned that when I see instructions to machine countersink thin material, it's probably because they want you to double flush rivet the assembly.