Drill Size for Wing Skins

WingsOnWheels · #1 06-15-2009, 12:40 PM

I'm building an 'extra' slow build RV-6A (the 'extra' is because this kit has no prepunched parts).

The wing skins to be dimpled are all drilled with a #41 (per the manual). I noticed that none of the current builders tools kits (Avery included) include a #41 bit as part of the kit only #40. I am assuming that these kits are centered around the new pre-punched aircraft.

Qustion: has the builders manual changed to recommend a #40 bit? If so, any idea why? Dimpling a #40 hold will oversize it and AD3 rivets will fit pretty loose. Are the skins thicker on the newer models? Just wondering if something changed, or the tool kits are just off the mark...

caryr · #2 06-15-2009, 12:48 PM

.096" #41
.098" #40

I doubt 2 thousandths inch will make much difference either way on rivet holes

WingsOnWheels · #3 06-15-2009, 12:58 PM

Quote:

Originally Posted by caryr

.096" #41
.098" #40

I doubt 2 thousandths inch will make much difference either way on rivet holes

Very true. I'm guessing by your post that the 7 builders manual recommends a #40 then...

#4 06-15-2009, 02:59 PM

I used #40 and #30 for all of the 3/32 and 1/8 rivets (respectively) on my slowbuild -6, and they worked just fine. You are correct that once a hole is dimpled it opens up somewhat and gives a looser fit, but a properly driven rivet of correct length will fill that hole nicely and give a tight joint.

As caryr points out, #40 is only .002" greater in diameter that an #41, and there are lots of other factors that go into giving you a nice round hole of the correct size (drill bit geometry, sharpness, operator skill, etc.)

Build on!

WenEng · #5 06-15-2009, 03:23 PM

to use #41 but you will see and ''feel'' a little more side slop when you set the rivet into the hole. However, as a previous responder mentioned, when you squeeze the rivet it works out just fine either way. If you are prone to extra reaming of the hole with your bit when you drill, you will notice more slop and I would suggest practicing with the drill stops. They help minimize the amount of reaming your holes get.

Flying Scotsman · #6 06-15-2009, 11:51 PM

We used #40 for all the -3 rivet holes, per the instructions and all the charts I've ever seen (not that I'm an expert, for sure) that list clearance holes for different rivet sizes.

I'm using a #40 reamer, though, for match-drilling anything that is pre-punched wherever I can (and oftentimes if I'm drilling a new hole, I'll drill it undersize and then ream to #40). Makes a much nicer hole.

And at times, I'll use a #41 to drill the head off a flush rivet, then pop it off with a punch, and then drill the remaining shank of the rivet out...I might be fooling myself, but it seems to help prevent oversizing the hole (at least, not as much) thereby preventing the need for "oops" rivets (NAS 1097s, I think they are...right?).

YMMV.

Steve

Flying Scotsman · #7 06-16-2009, 12:13 AM

Quote:

Originally Posted by WenEng

to use #41 but you will see and ''feel'' a little more side slop when you set the rivet into the hole. However, as a previous responder mentioned, when you squeeze the rivet it works out just fine either way. If you are prone to extra reaming of the hole with your bit when you drill, you will notice more slop and I would suggest practicing with the drill stops. They help minimize the amount of reaming your holes get.

I like the drill stops *a lot* when drilling out a rivet...keeps the drill from punching through suddenly and having the chuck mar the skin if it contacts it. Also, there are a few places where you'll want to use them when drilling in close quarters with something nearby (on the far side of the hole you're drilling)...like the skin, when doing some drilling on the forward fuselage/firewall stuff. Nice little addition to the tool box...

WingsOnWheels · #8 06-16-2009, 05:51 AM

The main reason I asked this question is that I have always used a #40 with 3/32 rivets in the past. When I saw the callout in the manual to use #41 it threw me off a bit since I had always seen other builders use a #40. I will say, the #41 does give a better "feel" when driving the rivet than an #40 hole does, but the difference is minute.

I agree about the drill stops - one of the best tools to have around. I keep my stops on most all the time. I try to prevent even the stop from hitting the skin, but it is nice to have it there in case of a slip - better the stop than the chuck.

I'm using split-point colbalt bits for the most part. So far I have had little issue with oversizing or out-of-round holes - lets hope it stays that way...haha