Drilling to size

[LettersFromFlyoverCountry]

Just curious. Do people actually get LP pop rivets into the drilled skin on RV-12 projects without drilling holes to a #30, which apparently they already are?

I'm still getting use to the "it's-pretty-much-all-done-for-you-already" nature of the RV-12 and while working on the trim assembly in the emp kit, noticed that the only holes the builder is asked to drill to full size are the 8 holes on the trailing edge of ribs. They're obviously undersized to begin with.

The other 12 holes (each side) are already drilled proper size. Cool.

Just for kicks, I tried inserting the pop rivet in just the alredy-drilled-to-size holes and it's certainly a struggle if it goes in at all. I assume a regular old 426 or 470 rivet would slip in fine.

I'm sure the company knows way more about this than I do, but it just feels to me that forcing those pop rivets in there is doing more damage to a very thin skin than drilling it out to a #30.

Now, it's true, I suppose, that drilling to a #30 would make the hole larger than it should be, which presumably presents its own set of problems.

And I also presume this is a much more vexing for people who've built older Van's kits and are transitioning to the more simplified versions.

[Aircraft Specialty]

Originally Posted by LettersFromFlyoverCountry

Just curious. Do people actually get LP pop rivets into the drilled skin on RV-12 projects without drilling holes to a #30, which apparently they already are?

I'm still getting use to the "it's-pretty-much-all-done-for-you-already" nature of the RV-12 and while working on the trim assembly in the emp kit, noticed that the only holes the builder is asked to drill to full size are the 8 holes on the trailing edge of ribs. They're obviously undersized to begin with.

The other 12 holes (each side) are already drilled proper size. Cool.

Just for kicks, I tried inserting the pop rivet in just the alredy-drilled-to-size holes and it's certainly a struggle if it goes in at all. I assume a regular old 426 or 470 rivet would slip in fine.

I'm sure the company knows way more about this than I do, but it just feels to me that forcing those pop rivets in there is doing more damage to a very thin skin than drilling it out to a #30.

Now, it's true, I suppose, that drilling to a #30 would make the hole larger than it should be, which presumably presents its own set of problems.

And I also presume this is a much more vexing for people who've built older Van's kits and are transitioning to the more simplified versions.

A #30 reamer will be your friend during the rv-12 build. Happens with a lot of holes. Running the reamer through will give you a nice clean hole and the rivet slides right in. You can see just a tiny bit of metal shavings that comes off when reaming the holes and there is no forcing of rivets required.

Steve

[Cyclone]

I have read accounts of 12 builders requiring only an occasional touch up installing pulled rivets into the skins. That was not my experience. With surfaces scuffed, deburred and thoroughly clecoed, less than half would install without torturous twisting, turning and a dose of French thrown in. I used a #30 bit with a stop and a couple of revolutions at low speed and moved on. I much preferred the result, especially after displacing a rib tab by trying to force a rivet.

[LettersFromFlyoverCountry]

Originally Posted by Cyclone

I have read accounts of 12 builders requiring only an occasional touch up installing pulled rivets into the skins. That was not my experience. With surfaces scuffed, deburred and thoroughly clecoed, less than half would install without torturous twisting, turning and a dose of French thrown in. I used a #30 bit with a stop and a couple of revolutions at low speed and moved on. I much preferred the result, especially after displacing a rib tab by trying to force a rivet.

Yes, I agree with this. I think trying to make a pop rivet go where it doesn't want to go is just inviting deformed holes and goodness knows what else.

[rv9builder]

I think the LP4-3 rivets vary slightly in size. I wish I had a digital caliper so I could confirm this.

I?ve tried to fit LP4-3 rivets through several parts before they were deburred or clecoed together. The LP4-3s wouldn't fit, but a #30 drill bit would. I then tried a second #30 bit, and it fit, too. Next step was to try some AN470AD4 rivets and, of course, they also fit perfectly. I estimate less than 5 to 10% of the LP4-3s I've used so far are small enough to fit without slightly enlarging the hole.

What's interesting is how little material you need to remove to get them to fit. With the parts Clecoed together, passing a #30 bit or reamer through the pre-punched hole at low RPM seems to remove just enough material to make the LP4-3s fit.

[rongawer]

Originally Posted by Aircraft Specialty

A #30 reamer will be your friend during the rv-12 build. Happens with a lot of holes. Running the reamer through will give you a nice clean hole and the rivet slides right in. You can see just a tiny bit of metal shavings that comes off when reaming the holes and there is no forcing of rivets required.

Steve

I second this. There are couple types of reamers though, so if you're reaming out a blind hole (i.e. you can't get to the filings behind, as in a wing skin), you'll want one more like this:
Alvord Polk 127-1 High-Speed Steel Chucking Reamer, Right Hand Spiral Flute, Round Shank, Uncoated Finish, Size: #30

They're not cheap, but the flutes will pull the filings outward and works very well and should last the life of the build without issue (mine is on it's second build). I have it in a hand-held chuck and just insert the reamer into the hole and give it one or two turns by hand; that usually does the trick. If you have an open hole to the backside, then a straight cut reamer is great too, and generally less expensive (I recommend Isham or Cleaveland tools). As an option, you could chuck the reamer in a cordless screwdriver/drill, but just don't overdo it by "drilling it" which could oversize the hole more than you want. The idea is to just make the hole fit, or reamed, to size.

Having said all that, when I have a stubborn hole, I ensure the best alignment with a tapered alignment pin (some folks use ice picks, but YMMV) first after clecoing every other hole. And then if the rivet won't work in without deflecting the metal, I ream it.

[rvbuilder2002]

The production specification for the RV-12 parts is that the holes get punched to .1285 (#30). As with most things manufactured there is an allowable tolerance , so it could vary from that a little bit.

The same tolerance exists for the manufacture of the rivets, so their diam. can vary a little bit as well. These tolerances can work against each other to make insertion of an LP rivet difficult.

Another big influence on ease of insertion is the alignment of the holes between two parts. A common cause of mis-aligment is from being too casual about flutting/straightening of curved parts.

Add all of these together and in some instances it can mean difficulty inserting rivets.

Many RV-12's have been built with minimal reaming/final drilling (it is the best way to enlarge a slightly undersized hole, but a drill bit is fine also) of holes. If one requires a lot more, it is not an indication of a bad thing, it could just be a box of 10,000 rivets that are at the large end of their tolerance range.

A good assembly technique is to use a tapered awl in a hole adjacent to the one you are inserting a rivet into. Wiggle that awl as you wiggle and use light pressure on the rivet. If it wont insert, then try final drilling while the awl is still in the adjacent hole.

My comment in a previous thread regarding final drilling was a caution against arbitrarily doing it for every hole without even knowing if it was needed. This is a sure way to end up with a lot of ovaled/enlarged holes when the actual difficulty is caused by hole misalignment that might be able to be correct in another way.

[LettersFromFlyoverCountry]

Obviously with the old 7A instructions, you can spend a long time looking at the ISO and seeing the big picture. The one warning that everyone has given me on the 12 is the instructions HAVE to be taken literally. Doing that, it's just hard to know when a hole is already "final size" and when it's not.

Take the nutplate attach holes on the stabilator, for example.

Instructions says, of course, to machine countersink in 16 places. Cool. Easy peazy.



Unless you drill those out to a #40, you're just NOT going to get a countersink in there. As you can see, an AN426-3 doesn't fit.

Now, if I take it literally -- since there was no mention of final drilling before countersinking-- my first reaction, "Whoa!" (Which, for the record, is what brought me home from the hangar early today . :*) )

By comparison, the #40 holes for the attachment of the "horn" on the anti-tab servo? Perfect.

But, yeah, I totally get what you mean w.r.t. arbitrarily final drilling.

[rvbuilder2002]

Originally Posted by LettersFromFlyoverCountry

Obviously with the old 7A instructions, you can spend a long time looking at the ISO and seeing the big picture. The one warning that everyone has given me on the 12 is the instructions HAVE to be taken literally. Doing that, it's just hard to know when a hole is already "final size" and when it's not.

Take the nutplate attach holes on the stabilator, for example.

Instructions says, of course, to machine countersink in 16 places. Cool. Easy peazy.



Unless you drill those out to a #40, you're just NOT going to get a countersink in there. As you can see, an AN426-3 doesn't fit.

Now, if I take it literally -- since there was no mention of final drilling before countersinking-- my first reaction, "Whoa!" (Which, for the record, is what brought me home from the hangar early today . :*) )

By comparison, the #40 holes for the attachment of the "horn" on the anti-tab servo? Perfect.

But, yeah, I totally get what you mean w.r.t. arbitrarily final drilling.

Ok, consider it mentioned....
If a standard rivet wont go in the holes, assume tolerances are working against you (from my previous post) and you should final drill.

[LettersFromFlyoverCountry]

Originally Posted by rvbuilder2002

Ok, consider it mentioned....
If a standard rivet wont go in the holes, assume tolerances are working against you (from my previous post) and you should final drill.

Ha! Excellent!

The biggest lesson I've learned on the 12 so far compared to a 7 is you can NOT make a mistake. (Well, obviously, you CAN, but the options are much more limited on the 12).

I mean, sure, the first reaction -- particularly for a previous builder -- is, "well, geez, any dummy can do this." But that attitude quickly will kill your wallet. The more simple instructions require as much concentration, thought, and understanding on what you're doing as any other kit.

I know that sounds obvious.