Riveting questions

[mustanglover]

Brazier Head rivets are different than Round Head rivets.........look it up.

Also the smaller head countersunk rivets are referred to as NAS1097 rivets. These are used all over aircraft today. The "countersink" uses less material depth and can be used in structural applications. Too many people use AN426 rivets on skin,s which are typically .032 thick, and this causes a knife edge condition at the bottom of the countersink (unless you shave the head down, which has it's own problems structurally) and can lead to fatigue cracking of the skin.

Most (not all) WWII era aircraft have dimpled or hot dimpled countersinks.

[mustanglover]

Finally a number of years ago Boeing developed a new protruding head rivet. It is similar to the AN 470 rivet except the edge is more vertical, sort of like a round head with the top flattened. It is marked with a raised circle. You wouldn't want to see any of them on a restoration.

That is a Briles rivet, and they come in both countersunk and protruding head styles. The countersink is somewhat stepped rather than a uniform angle and the head of the protruding head is exactly as you described.

S

A rivet which has a flat crown that extends from the head of a rivet. The rivet is typically installed into a workpiece hole which has a countersink. The head has a frusto-conical section that extends from a rivet shank and a cylindrical section that extends from the frusto-conical section. The frusto-conical section sits within a countersink of the workpiece hole. Extending from a top surface of the head is a crown which has a flat end face and a tapered portion that extends from the end face to the top head surface. The crown has a diameter that is smaller than the outer diameter of the head. The flat end face is approximately 0.5 times the diameter of the shank. The crown has a diameter that is approximately 1.25 times the shank diameter. The rivet is deformed by a hammer and an anvil so that the crown becomes flat and the rivet fills the hole of the workpiece. The crown maintains essentially the same diameter during the rivet deformation process so that the deformation forces are transmitted primarily through the shank of the rivet. The rivet head completely fills the workpiece hole without requiring any post-installation shaving process.

See http://www.freepatentsonline.com/5580202.html

[muddyboots]

[JDK]

And there'll be a quiz to see if you've been paying attention...

[Hemiman]

Finally a number of years ago Boeing developed a new protruding head rivet. It is similar to the AN 470 rivet except the edge is more vertical, sort of like a round head with the top flattened. It is marked with a raised circle. You wouldn't want to see any of them on a restoration.

That is a Briles rivet, and they come in both countersunk and protruding head styles. The countersink is somewhat stepped rather than a uniform angle and the head of the protruding head is exactly as you described.

S

And a royal pain in the a-- to drive!!! ( 767 belly skin repair)

[bdk]

Finally a number of years ago Boeing developed a new protruding head rivet. It is similar to the AN 470 rivet except the edge is more vertical, sort of like a round head with the top flattened. It is marked with a raised circle. You wouldn't want to see any of them on a restoration.

That is a Briles rivet, and they come in both countersunk and protruding head styles. The countersink is somewhat stepped rather than a uniform angle and the head of the protruding head is exactly as you described.

Briles rivets were developed by the Briles Corporation, not Boeing. They were used on the C-17 for a time but they were discontinued because they are very expensive to install and the heads tend to pop off in service.

[skymstr02]

I became familiar with the Briles rivets working on Embraers. It seems that several Boeing engineers became ex-pats, and moved to Brasil, and took their nasty habits with them.

[bdk]

I didn't realize that Boeing Commercial even used them until now. They work great in a perfect world, but are problematic in a production environment. There just isn't much room for error in the countersinking operation. When you are countersinking thousands of holes at a time, the special cutters can wear out quickly. This isn't such a big problem with conventional countesink cutters.

[Second Air Force]

I didn't realize that Boeing Commercial even used them until now. They work great in a perfect world, but are problematic in a production environment. There just isn't much room for error in the countersinking operation. When you are countersinking thousands of holes at a time, the special cutters can wear out quickly. This isn't such a big problem with conventional countesink cutters.

Yep, the 767, 757, etc. all use the Briles design. I'm normally a systems/powerplant guy but have done a few repairs years ago. Once you get a good countersink and properly adjust it the process isn't too bad. It does take a little more practice to get the tooling set up. Driving the rivets isn't bad if you have a competent partner.

S

[drgondog]

The key to flush rivets is to a.) disrupt as little surface flow as possible, and b.) maintain enough distance from the edge to reduce tearing/rupturing the skin edge in shear.

The design rules say 2xdia distance from panel edge for a flush rivet and 1 1/2 for round head. The key to the flush rivet is to a.) have enough 'rivet shank area' to resist the shear forces imposed by the panel on the rivet (i.e. rivet failure), and enough sheet thickness/area in contact with the rivet in the remaining (non counter sunk) material in the panel to resist local failure (due to bearing stress) of the panel.

Dimpled sheet/panels are stronger than countersunk, but there is a sheet thickness threshold (and expense) in which dimpling no longer feasible.

The AN 426, brazier head, 100 degree countersunk flush rivet has been around forever, and certainly for WWII a/c

[John Dupre]

I haven't got a source for the current practice of allowing a flush rivet head to be slightly above the level of the skin except that I read about it and the Briles nee' Boeing rivet a few years ago in an industry magazine. It comes to me now that there was another change with flush rivets going to a 120 degree angle this was also attributed to Boeing. Could that be the same as the Briles head flush rivet? I don't recall the article mentioning the cutter being stepped.

As for warbirds I just read my copy of Aircraft Riveting by Nitsa and it mentions using a 6 inch scale placed along the row of rivet heads and there should be no light showing between the skin and rivet heads and the edge of the scale. So that must mean they wanted the heads perfectly flush. It would be interesting to know if manufacturers or other users allowed any variation.

[fighter_ace06]

We have been going back with the original AN-456 "Braizer" and AN-430 "Round Head" rivets on our Wildcats. A good example of the domed head countersunk can be found on the leading edge of the stub wings on a wildcat. I cant remember the name of the company I have been getting my rivets but I will look it up. You can get the sets from US Tool.

[ZRX61]

As for warbirds I just read my copy of Aircraft Riveting by Nitsa and it mentions using a 6 inch scale placed along the row of rivet heads and there should be no light showing between the skin and rivet heads and the edge of the scale. So that must mean they wanted the heads perfectly flush.

That's how I was taught to do it. I still have all the 3x4in & 6in sq test panels in one of my toolboxes...