Rivets - simple misunderstanding or misled by liars?

[wktaylor]

AN426 and AN470 spec sheets explicitly omit any mention of non-table lengths. Hence the option -2 or -29-and-above are prohibited.

MS20426 and MS20470 both explicitly allow: (a) table-nominal; (b) nominal + 1/2-grip lengths; and (c) nominal off-table grip-lengths [so -2 and -29-and-above would be permitted]. HOWEVER, any off-table lengths are likely 'special order' $$.

Extreme Large Dia solid rivets are best installed by (a) 'squeeze' methods or (b) freeze/shrink-fit and then peen or swage the edge over the lip of the hole for mechanical retention.

Be cautious regarding use of 3/32 protruding-head ILO 4/32 flush or protruding head... without explicit drawing approval. Shear strength of 3/32 protruding head is inferior to both 3/32 dimpled install... and inferior to shear/tensile strength of 4/32 protruding head or flush/dimpled installs.

 

[rdj]

I never thought of a “rule of thumb” as a person.


BJC

Sorry, my writing is getting sloppy.

In my original post, the "persons" I implied were incorrect were the authors of the articles in Kitplanes and Sport Aviation who penned the "rule of thumb" that a solid rivet tail needed to be 1.5x the rivet diameter. The reason I believed they were wrong was because Aircraft Spruce carried rivets that clearly could never meet that rule of thumb, because the Hanson Rivet catalog mentions a "clinch allowance" that appears to be same thing as "exposed rivet tail" that is more like 1x, and that McMaster-Carr MS20470AD rivets specify allowable max material thicknesses that also are thicker than allowed by 1.5x "rule of thumb". That's what I found when shopping for some rivets I need, and which prompted my original post.

However, after doing some more book research and math, it appears that the 1.5x diameter "rule of thumb" actually is well-accepted and matches the MIL spec. Therefore, the article authors are correct and the catalogs appear to be incorrect, at least for the commonly used rivet sizes. That said, it also appears that there are indeed some solid rivets for which those rules are meant to be broken, as OBwanBD5, cvairwerks and others point out in their fascinating posts.

Anyway, I apologize for throwing shade at those authors in my OP.

It's also been quite the thread on rivet applications. As someone who knows next to nothing about solid rivets, book knowledge is one thing but nothing beats the field experience of others on this forum. Interesting stuff!

Bob

 

[David Moxley]

WK- It's been probably 22 years since I did that repair. Diameter was 28 and length would have been somewhere around a -5. We had to plug 4 or 5, 7/8" holes that were miss drilled in a high stress bulkhead. We could only do a small 100 degree chamfer, instead of a normal countersink. Engineering called for making up the DD's and driving them double flush. Both sides were then shaved, sanded and lightly polished to match the bulkhead contour. When correctly drilled, the new hole would cut out about 1/4 or so of each plug. The repaired holes then had Ti sleeves bonded in them and ever so slightly reamed for fastener clearance. Nerve wracking, as screwing up the repair would set that a/c back about 3 weeks and several hundred manhours of tearing it down to drill a new pair of bulkheads to fit.

Just curious, my 4x rivet gun does the little ones I have needed from glider to gulfstream…3-6 diameter. What kind of gun will drive a 28-5? I’m certainly not disputing it was done, but that one will take quite a punch to drive! And quite the bucking bar. I’d love to see the tools!

This this should do the job !

 

[cvairwerks]

Dave: I’ve got a 12”, a 24” and 2 36” ones to overhaul for my home shop. Missed on a couple of 60” auto riveters they were getting rid of, long years ago at work. Would have been a heck of an operation to drag that 36” unit up on the backbone and hold it sideways to do those big rivets.....

 

[wktaylor]

I have been a fastener weenie since the late 1960, helping my dad build his T18... thru my professional years up-to-today. I appreciate these small/vital parts in all their weird/diverse forms. And believe me the diversity is huge.

There is a LOT of info on fastening that I'm getting together for my engineering team. The non-proprietary stuff has been scanned/zipped... files are pretty large.

I've attached one of the smaller files. This is just a tiny sample of the many larger books [scanned-to-files], all eras, that I have found thru the years.

 

[rdj]

I have been a fastener weenie since the late 1960, helping my dad build his T18... thru my professional years up-to-today. I appreciate these small/vital parts in all their weird/diverse forms. And believe me the diversity is huge.

There is a LOT of info on fastening that I'm getting together for my engineering team. The non-proprietary stuff has been scanned/zipped... files are pretty large.

I've attached one of the smaller files. This is just a tiny sample of the many larger books [scanned-to-files], all eras, that I have found thru the years.

Interesting how "bucked-tail" and "stick through" in 1942 became "bucktail" and "exposed tail" or "clinch allowance" today. I prefer "stick through"--it's far more descriptive

 

[geraldmorrissey]

I could be wrong but the picture shown appears to be a hot dimpler.

 

[cvairwerks]

Only difference between a riveter and a hot dimpler is what dies are installed and the heating elements. Leave the heat off and snap in the appropriate rivet dies and rivet away.

 

[pfarber]

I find it hilarious that no has cited the real 'recommended' shop head as 1.3 to 1.8 with 1.5 being optimal.

So you have a wide variable to FAA recommend shop head dimensions.

The head does nothing but keep the rivet in the hole. Remember rivets should only see shear loads... Something the the head has nothing to do with.

 

[Mark Z]

A long and straight row of well shot/bucked rivets is pure art at the finest.

 

[Angusnofangus]

A long and straight row of well shot/bucked rivets is pure art at the finest.

My favourite part of sheet metal work.

 

[cvairwerks]

Hundred or more rivet guns going at the same time used to make some great music. Listen close and you could tell which pair of guys/gals were really in sync, by their rhythm and timing.

 

[Angusnofangus]

Trying to rivet with someone that you are not in sync with is a real PITA. More than once have I wanted to reach around and give the other guy a good cuffing.

 

[Pops]

My daughter and I have done a lot of riveting together and we stay in sync most of the time. No one has to say anything. We both enjoy it.

 

[kjlpdx]

I find it hilarious that no has cited the real 'recommended' shop head as 1.3 to 1.8 with 1.5 being optimal.

So you have a wide variable to FAA recommend shop head dimensions.

The head does nothing but keep the rivet in the hole. Remember rivets should only see shear loads... Something the the head has nothing to do with.

yes and no, a countersunk rivet significantly increases the shear strength in that the diameter is increased, so
stronger tha a non-dimpled rivet.

 

[David L. Downey]

I find it hilarious that no has cited the real 'recommended' shop head as 1.3 to 1.8 with 1.5 being optimal.

So you have a wide variable to FAA recommend shop head dimensions.

The head does nothing but keep the rivet in the hole. Remember rivets should only see shear loads... Something the the head has nothing to do with.

With AD aluminum rivets, the dole diameter and quality (including the deburring quality), the initial tail protrusion length in terms of undriven shank diameter, and the finished ta height/diameter all contribute directly to the shear strength developed while expanding the shank to fill the hole. That very expansion, work hardening the rivet shank and tail, is exactly where the stated shear values come from.
Too small a hole and/or an under driven tail = subspec shear strength.

 

[BBerson]

None of that matters on thin skin. A typical sport plane like a Zenith is assembled with Avex blind rivets with almost no shop head and hollow core. A driven rivet for a home made thin skin airplane doesn’t need the same shop head standards as Boeing. The spar has different standards and it's easier to make a full shop head on a heavy spar without skin damage.

 

[Angusnofangus]

None of that matters on thin skin. A typical sport plane like a Zenith is assembled with Avex blind rivets with almost no shop head and hollow core. A driven rivet for a home made thin skin airplane doesn’t need the same shop head standards as Boeing. The spar has different standards and it's easier to make a full shop head on a heavy spar without skin damage.

I couldn't disagree more about shop head standards. Some aircraft manufacturers might have very minor differences in their production standards, but they are VERY minor, a few thousandths of an inch maybe. It doesn't matter if it's in thick or thin skins, an acceptable rivet needs to meet certain dimensions of the shop head in relation to the diameter of the rivet. Rivets are shear fasteners, which is why Boeing is able to use reduced head rivets, mainly in skins.

 

[BBerson]

Do you have any experience with Avex rivets?

 

[Angusnofangus]

Do you have any experience with Avex rivets?

No, but I have had a personal relationship with at minimum 1million solid rivets. I do know that they are not comparable to solid rivets and are not substitutable on a one to one basis. Even CherryMax are not one to one replacement for solids.