Rivet Hole Size

I painstakingly drilled out 310 rivets on my outboard upper wing skin, (don?t ask me why) using the procedure outlined by Walt Aronow , drill the head, break the head off, pop the rivet tail out. I didn?t even remove the tails until the skin was removed. It was easy enough to just pull them out from the backside. I?m thinking ?That wasn?t so bad.?
Ok?here is the dilemma I?m faced with. According to MIL-R-47196A, 3.2.1.3. Hole size. Hole size for rivets shall conform to Table I unless otherwise specified on the engineering drawing or specification. Table 1 calls out the min/max for a 3/32 rivet as .093/.103 respectively.
I used a #37 drill bit with a diameter of .104 as a no go gage, I figured if it fit through the hole I f?ed up and would have to use a NAS1097 rivet. The first thing I did was check all 75 of the machine counter sunk holes on the wing spar flange. The #37 drill bit didn?t fit in any of them, yea for me. Next I checked the dimpled rib holes and, son of a!@#$ , it went through every single one of them.
Contemplating the horror in front of me, I got to thinking, sometime that?s a bad thing, what?s the size of a newly dimpled #40 hole? So I grabbed some scrap .025, the same thickness as the ribs, and drilled a nice crisp #40 hole and dimpled it with spring back dimple dies. Low and behold the #37 passed right through.
3.4.1. Oversize rivet holes. When rivet holes are enlarged beyond specified tolerances, the next larger rivet size (diameter) may be used provided the row spacing, pitch and edge margin minimum are maintained and the requirements of paragraph 3.4.3 are not exceeded?.
I call an A&P I know and explained my dilemma. He said I was overthinking the issue. And told me to use NAS1097 rivet if I was concerned. However Section 3.4.3. Repair limitations. The combined oversize rivet hole repairs and oversize countersink repairs shall be limited to a maximum of 20 percent of the rivets, or 10 rivets in a single rivet pattern, whichever is less. Repairs to more than two adjacent oversize rivets, or replacing more than half the rivets with oversize rivets in any 10 inch length of pattern is prohibited.
That many reduced rivet head on the low pressure side of the wing causes me pause.
Am I overthinking this?

jaradtke said:

So I grabbed some scrap .025, the same thickness as the ribs, and drilled a nice crisp #40 hole and dimpled it with spring back dimple dies. Low and behold the #37 passed right through.

Click to expand...

You're overthinking it.

Put a micrometer on the newly dimpled test piece and get an idea (note: an idea, not a go/no-go value) of how big the properly drilled and subsequently dimpled hole is. Then grab a drill bit of appropriate size to use as your test gauge for the drilled-out holes. If it doesn't go through, then the drilled-out hole is good. If it does, then you may have to inspect it a little more to see if it's considerably larger and/or oblonged or something, and needs an "oops" rivet.

That'd be what I'd do...others may have different suggestions.

I wondered about this effect during the entire build...here I was reaming holes to #40, and then turning around and dimpling them, which *obviously* makes 'em bigger...how much? Not sure, but that's the accepted method, so it must be okay, even though the dimpled hole is definitely larger than what it was when it was originally match-drilled....

I wondered about this effect during the entire build...here I was reaming holes to #40, and then turning around and dimpling them, which *obviously* makes 'em bigger...how much? Not sure, but that's the accepted method, so it must be okay, even though the dimpled hole is definitely larger than what it was when it was originally match-drilled...

Click to expand...

I must say that I wondered about this as well during my build. I also found that after a rivit had been fitted and then removed the hole was even bigger, it appeared to have stretched.

CALL VANS! You likely are overthinking the situation but the rules on rivet replacements with 1097's are pretty hard and fast. The 1097's fit nice and look pretty in an oversized hole but they do NOT have the structural strength of a normal sized rivet.

I am glad to see this thread. As a new builder - recently started my -10 tailcone - I feel like I could ask 20 questions every day. This was one that has been in the back of my mind from my first day of riveting. I began using substructure dies - I could visibly notice the dimpled holes looked larger - micrometer confirmed all several thou outside the MILSPEC 3/32 limit. I have since been using standard dies for everything. Skins look just as nice but the shop head is better. Certainly the learning curve had to do with my shop head quality, but the holes certainly were not helping as things went much smoother with the standard dies used on both surfaces.

I sent a RFI off to Van's.

Van's Response

Build on

"Your A&P is right. You're over-thinking this. By quite a bit.

From the beginning of time we have riveted RVs (and many other airplanes) together with dimpled #40 holes that are stretched beyond #40. They do not come apart.

Go thou and do likewise.

If your holes are not enlarged past the original, use the original rivets to put things back together.

And don't drill out any more rivets unless you're removing a damaged part. One of the reasons airplanes use so many rivets is so that you don't have to absolutely depend on one or two. If you mi**** a few, just leave them and move on."

See...all is well. One of the best things about Vans is that they have put me at ease many, many times. I honestly have to speak from personal experience that they are one of the best, if not the best, companies I have done business with. They tell the truth (always) and are always there for the customer. Probably the reason they are the most successful kit manufacturer.
Build on...have fun!