F-783B and F-782B - dimpled. Did I screw up again?

[tegwilym]

I'm starting the fuselage and am working on the main bulkhead. I was working on those little rib things F-783 and F-782 that go on the fwd bulkhead.
I have them all done, but then looked at how the nutplate fit and realized that maybe dimpling wasn't right and should have been countersunk instead?
Arrgh!

I have a feeling this is just another one of my screw-ups even after reading and studying the drawings many times.
Can I rivet those nutplates on the way it is? Are they structural? Reverse dimple the holes and countersink? Or the dreaded and familiar "go on Van's site and order new parts"?

Thanks,

Tom
Empennage done, fuselage started - RV7A

[DaleB]

Hi Tom,

Those parts support the fuel lines and a cover screws to the front. They should get dimpled, the metal is too thin to countersink for a regular rivet. You'll also need to dimple or countersink the nut plates... get used to that, there's a lot of it to do on the fuselage. You can also use NAS1097 reduced head rivets ("Oops rivets") and lightly countersink the sheet metal, but then you will have to drill out all the nut plates.

I have done both, but drilling them out was more of a PITA then dimpling. I modified a female 3/32" dimple die by grinding/filing off one side to clear the "barrel" of the nut plate.

[tegwilym]

Ah! Ok, that makes sense. I did Google "dimple nutplate" and realized I just do the same thing as usual, but put the nutplate in there.
I figured the metal was close to being too thin for a countersink, but then when I placed the nutplate on, there was a gap due to the raised dimple and started questioning myself again.
I'll give that a try. Thanks for the quick reply!

Tom

[BillL]

Tom, dimpling the nut plates is good for this situation where you are already halfway there (dimpled skin), but you should get some -3 NAS1097 rivets for future nut plates. You can use the NAS rivets, flush, with no work to the nut plate even in .025" material. 5-6 rounds with the deburring tool is sufficient for the heads. This will save you many many hours over the build. I guarantee that you will like them after you do a few. Easy to drill out just like standard rivets.

I don't like using my expensive dimple dies on steel parts.

Only Vans calls them "oops", and Vans has the -3 and -4 in stock, but don't list them. I got -3-3, 3.5, and 4 solely for installation of nut plates. The -4 sizes are for oversize hole mistakes. (oops!)

[tegwilym]

Learned something else new about rivet variations. I'll look into some of those too, that looks like a good way to do it. Looking at the photo of the rivet, it makes sense too that just a very slight countersink will be enough for the small head.
Thanks!