Drilling out rivets

[papakeith]

Y'all are going to have to bear with me for a bit . I'm going to be asking any number of basic questions.

Here's today's:

Lets say I put a smilie in a 3-3 470AD rivet (not that I have of course )and it needs to be removed. What is the preferred procedure to remove the offending rivet?

[cjensen]

There are two ways. One is to buy a rivet removal tool that will center the drill bit on the head every time. Makes it a snap.

The other is to simply use the dimple in the head of the 470 rivet to center your drill bit, and work the bit slowly in to the head until it won't slide off the rivet.

Either way, just drill far enough to snap the head of the rivet off, and use a punch to knock the shop formed portion out.

[cjensen]

Oh, your bit needs to be same size as the rivet. AN3's use the 3/32 bit, AN4's get the 1/8 bit, and so on...

[bullojm1]

Keith-

Drilling out rivets is pretty easy. The basic idea is you want to drill starting on the manufactured head (the round head with the dimple in the middle). Use the dimple to act as a guide and only drill through enough to get a pin punch ( http://www.averytools.com/p-79-18-drive-pin-punch.aspx ) in there to break the head off. Now, there is a fine line here -- go too deep and you risk oblonging the hole. Go to shallow and the punch won't have enough bite to break the head off. Once the manufactures head is off, use the punch to tap the other side out of the hole.

If you do oblong the hole a little, its no big deal. The rivet expands when it is set and typically will fill any inconsistency in the hole.

Good Luck!

[Lorin Dueck]

Papakeith -

Check out the " Drilling out a driven rivet" video on EAA Hints for Homebuilders site.

http://www.eaa.org/video/

Look in the upper right corner for EAA Video Galleries.
Click on "Hints for homebuilders" link.
Click the "Sheet metal" tab.
It the third video down....

Hope that helps.

Thx, Lorin D
9A Fuse SB
N194LD reserved

[dons]

I use the following procedure (for a 3/32" as an example) rivet and have only had to use an oops rivet twice, and I have drilled out hundreds of rivets (we won't go into why).

1) make sure there is a small dimple remaining in the factory head, if not make one with a punch
2) use a 1/16" drill bit to start
3) tilt the drill as it turns to get the hole eyeballed right to the center, it's ok if you don't have a 1/16" round hole on the surface at this point because you are going to be enlarging it, what is important is that it is centered where it goes to any real depth
4) drill right through the rivet and out the back end, this is not what a lot of people say, but I find it requires a lot less force to punch out if you weaken the rivet from the inside a bit
5) drill just to the depth of the factory head with a 5/64" bit making any very slight adjustments to get the hole centered, shouldn't be required after you get the hang of it with a 1/16" bit
6) repeat the above with a 3/32" drill bit just to the depth of the factory head
7) snap the factory head off with a 3/32" pin punch, by putting it in the hole to about the depth of the factory head, be a little bit patient here by breaking the head off a little at time while working around in a circle from where it first broke loose, if you are just a little off center, start the break where the hole is closest to the edge of the rivet hole and work around from there
8 ) use something with a hole in it just big enough for the size of rivet/dimple on the back side to support the material and punch out the remaining rivet, if you don't support the back side you can easily bend the material

If the rivets are being removed in a place where you can use a squeezer, use an undersized male dimple die to push the rivet out while again using something to support the back side that won't put pressure on the dimple if there is one or interfere with the shop side of the rivet falling out. I use things like a large female dimple die, just the hole in the squeezer, a 1/4" thick piece of wood with a hole in it, whatever works, just make sure the diameter is big enough so the rivet won't get jammed when it comes out.

If the hole you drilled though at 1/16" is very close to the center on the back side and you are having problems punching out the rivet, enlarge the hole all the way through to 5/64" and try again with the 3/32" punch as it will weaken the remaining rivet even farther and require less force to punch out the rivet.

I sometimes drill only as deep as the material, and back side dimple if there is one, with the smaller diameter bits to weaken the rivet. This is especially useful if you don't want shavings to get somewhere where it would be really hard to clean up, it does take more effort to stop at a proper depth, so I only do it if I have to. A piece of masking tape on the drill bit can easily mark the depth if need be.

Along the same lines as above, put a piece of tape over the shop side of the rivet if you don't want it dropping into somewhere you can't easily extract it later, when you punch it out it should stick to the tape and make it easier to get out of tight spots.

It all boils down to getting the factory head snapped off and being able to push the rest of the rivet out without doing damage to the original hole walls and surrounding material. Man, this was way too long, remember what you paid for this, and that's what it's likely worth.

[papakeith]

thank you all for your input. Hopefully I can manage this without buggering up the hole too much

[bullojm1]

Keith-

I would make some practice scraps of AL sheet and rivet them together. Then practice drilling out them before you do one for real.

[papakeith]

sounds like a wise course of action. Will do.

[Cherokee Driver]

I seem to have developed a lot of experience in a short time in this area (so we are clear... I am not particularly proud of this)

I have been drilling deeper than the surface of the metal being riveted with a drill one rivet size smaller which seems to make the knocking out stage easier.

Use a spring loaded punch on the dimple a couple of times so that there is a good drill purchase initially. I drill almost the length of the rivet, simply to leave some material for the punch to rest on in the knockout phase, with the smaller drill. The head often snaps with the smaller size with a little rocking. In using the smaller size, I often never even come close to "oblonging" the hole. It works for me...your mileage may vary.

[tmbg]

After you drill out a couple hundred of these, it will become such second nature that you won't go through all the trouble...

Center the drill using the dimple, go slow. Once you have it centered and started, you can drill all the way through the rivet and it will pop out without doing any damage to the hole. Usually, when I drill one and get it right, the head pops off and ends up stuck up the shaft of the bit, and the shop head pops out on its own.

If you drill it off center enough that it screws up the hole, chances are you'd have a hard time breaking the head off and punching it out even if you'd only drilled into the head.

Yes, it's entirely possible you'll screw it up and oblong the hole... oh well. If it's a skin rivet, drill to #30 and use a 1097-4. In your case, you're doing internal 470-3 rivets, if the occasional rivet ends up as a 470-4, it'll be obvious to the naked eye, but who cares in the grand scheme of things?

Obviously, it's entirely up to you how anal you get with it. Don's method is VERY accurate, and gives you an easy way to not screw up drilling, but that's way too many drill changes for my taste. I riveted my entire aft fuselage last night, 99% of the rivets came out SPOT ON PERFECT, and I drilled every one that was cleated or ugly in any way, even though I knew in my heart they were strong enough. I probably drilled two dozen rivets, and had to oops three of them. I'm not concerned about it, because it still looks fantastic from the outside, and it'll be plenty strong.

[bullojm1]

Keith-

Another option is to do nothing! A lot of times when you take a rivet out, you do more damage than good. A smiley is usually not a big deal unless the smile gets close to the center of the rivet. If your smiles are on the outer diameter of the rivet, I would say leave it.

[papakeith]

The drilling and removal went without a hitch. Not an oval hole to be found anywhere.

Thanks for all of your helpful hints.

Keith

[Mike Balzer]

The 7 Rule

-3 rivet use a # 40 drill 3+4=7
-4 rivet use a # 30 drill 4+3=7
-5 rivet use a # 21 drill 5+2=7 (use a 21 for better tolerances)
-6 rivet use a # 10 drill 6+1=7

Just drill the head enough to break the manufactured head off the rivet by taking the drill and wiggeling it in the hole or a 3/32 punch. I recommed you place a bucking bar next to the rivet before you punch it out to prevent the skin from pulling away.

I have worked as a structrual mechanic for the airlines and I have always used the same size drill for removing rivets as I would for installing them. For Saftey you may want to use a numbered drill bit one size smaller if your concerened about not being perfectly centered.

EX -3 rivet #40 drill to install and #41 bit to remove.

Hope this was helpful

Mike Balzer