Replicating a Hawker spun rivet joint

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Harvardiv

Active Member
Joined
Jan 2, 2007
Messages
41
A friend in GB posted this link for me on Practical Machinist:


Apparently the "T26" tubular rivet part is relatvely low tensile ("20ton") mild steel.



I drove 450+ of those things in the past month or so.
Mostly #10-24 & 1/4" - 20.
I doubt rivnuts have anywhere close to necessary shear unless filled with a tight fitting bolt.
Also doubt they make them long enough in the small sizes, but you could call.

Nonetheless, your note held a valuable hint!
It would be relatively easy/fast to make a simple, adjustable length, die set to pull-squeeze the tubular rivets with a typical large series pneumatic/hydraulic cherry or "pop" rivet puller. I made such a set to pull the riv-nuts, 1.)to save my aging wrists & 2.)to avoid the cost of the commercial spin-pull units. :)

(spin in this case does not refer to forming action, but to the capability of the unit to spin the rivnut arbor in the tool on or off at operator finger control, in a production setting. Rather than manually screwing the rivnut onto the arbor, then manually unscrewing the arbor aftter the rivnut is set)

smt
Hello SMT:

Show a picture of your rivnut set you made.
 

Harvardiv

Active Member
Joined
Jan 2, 2007
Messages
41
A friend in GB posted this link for me on Practical Machinist:


Apparently the "T26" tubular rivet part is relatvely low tensile ("20ton") mild steel.



I drove 450+ of those things in the past month or so.
Mostly #10-24 & 1/4" - 20.
I doubt rivnuts have anywhere close to necessary shear unless filled with a tight fitting bolt.
Also doubt they make them long enough in the small sizes, but you could call.

Nonetheless, your note held a valuable hint!
It would be relatively easy/fast to make a simple, adjustable length, die set to pull-squeeze the tubular rivets with a typical large series pneumatic/hydraulic cherry or "pop" rivet puller. I made such a set to pull the riv-nuts, 1.)to save my aging wrists & 2.)to avoid the cost of the commercial spin-pull units. :)

(spin in this case does not refer to forming action, but to the capability of the unit to spin the rivnut arbor in the tool on or off at operator finger control, in a production setting. Rather than manually screwing the rivnut onto the arbor, then manually unscrewing the arbor aftter the rivnut is set)

smt
Hello SMT:

Show a picture of your rivnut set you made. Would your tool work for 4130 tube rivets?
 

Aviacs

Well-Known Member
Joined
Oct 21, 2019
Messages
315
Show a picture of your rivnut set you made. Would your tool work for 4130 tube rivets
I'm traveling shortly and won't be in the shop today.
Will try to catch up with that tomorrow, since someone on PM also wanted to know how i was pulling rivnuts with a standard hydro/pneumatic "pop" rivet gun.

My point in this discussion is that i have experience using "pull" to compression set hollow rivets in the form of Rivnuts.

Extrapolating, dies could be made in a shape to form other hollow shapes.

The "complex" part of the existing rivnut puller is really the nose piece. The pulling part is simply a threaded stem and shank made from 4140 prehard. The shank fits the rivnut to prevent collapse, the threads fit the given size to pull. The nose piece is relieved (bored) to the shank size, and the stem is "as large as possible to still work with the largest (1/4" Pop rivets) available stock collets in the gun"

So in my rivnut pullers there is no "die". Just a removable threaded stem-shank-screw piece; + the nose piece to the gun to adapt it and actuate the collet opener.
As i envision the hollow rivet setter, the nose piece would be shaped to the head form, the threads of the stem would engage a small screw-on button die to shape the back side.

A hollow rivet heading die set could be made stronger than my rivnut setter stems - the shank could be made thicker and screw into the puller mechanism in the gun. Rather than be collet-gripped. Since the bottom/button die would need unscrewed each time anyway. The limit is the strength of the steel puller stem dia that would clear inside the hollow rivet. it is possible that the diameter could be insufficient, if the hollow rivet diameter is small and the walls thick.

Do you know a "typical" or reference ID & OD of the "T26" part?

smt
 
Last edited:

Aviacs

Well-Known Member
Joined
Oct 21, 2019
Messages
315
Per Harvardiv
Show a picture of your rivnut set you made. Would your tool work for 4130 tube rivets?
Here are the rivnut puller parts for a typcial air over hydraulic "pop" rivet puller.

I started by making a puller that screwed into the regular actuating parts, behind the collet, in order to use a thicker pulling stem.
That was too inconvenient. Without a spinning mechanism as the commercial units have, loading, and unscrewing the arbors was inconvenient and time consuming. So i changed to the system shown. Use the largest stem that will release from the largest collet set; & figure on replacing if/when they break. This is easy to finger set the rivnut on, and then finger-spin the arbor out of the set rivet. As noted previous post, they've pulled aprox 450 & counting rivnuts and no tool/mandrel failure yet, though they are getting chewed up. The parts are made of 4140 prehard. 28 - 32 RC, typically. My fear is that much harder (more tensile strength) would dull the collets and be counter productive. My go-to tool steel for "difficult" applications is S7. Possibly using that and going to maybe low 50's RC could add some strength for a tubular rivet setter. Or even sticking with 4140 & furnace hardening it here to the mid 40's.

DSC_0133.JPGDSC_0139.JPGDSC_0142.JPG

I may have been overly cautious making the arbors with the solid section, to support the upper, relieved portion of the rivnuts from collapsing. Only rarely do they seem to need it. Having added the solid support section, it became necessary to make nose pieces to accommodate them, bored to the specific size of each. Not sorry at all, but someone who wants to just set a few in non-critical app could probably dispense with that nicety, just thread the end of an arbor thin enough to be gripped by the large-series collet set, and pull most without trouble using the largest pop-rivet (1/4" body dia) nose piece.

Last sketch suggests shaped nose piece and back-die with long stem, for flaring hollow rivets.

Why i've been pulling lots of rivnuts. For one thing, the plywood is screwed on (removable) as are some of the internal panels and ducting. The plywood is just an outer final insulation and protection layer over a riveted sheetmetal case.

DSC_0091.JPG

Back to airplanes: What is a typical hollow rivet ID & OD?
My suggestion of adapting a puller was based on the original "T26" spec which is aprox "20 ton" tensile; IOW fairly "mild".
So it gets back to minimum ID you want to pull, and what is the wall thickness as aked in my post #64.

smt
 
Last edited:

Harvardiv

Active Member
Joined
Jan 2, 2007
Messages
41
Aviacs,
Kind of lost you there. I have not yet attempted to install rivnuts so I have no idea how this process works. Are you saying to use an elongated pop rivet stem, and create a custom die for a tube rivet? Can you sketch what you mean? Also, you talk about using T26, but from what I understand tube rivets are similar to grade 8 or 4130. So would need sketches and a statement of what tooling would be different than what is available for pop riveting.

Thanks,
 

Aviacs

Well-Known Member
Joined
Oct 21, 2019
Messages
315
Can you sketch what you mean?
Done, above.

Also, you talk about using T26, but from what I understand tube rivets are similar to grade 8 or 4130.
T26 is a British designation, included in the original spec someone else provided for the hollow rivet system.
If you read the other posts on the subject and the links, you can see what it boils down to.

similar to grade 8 or 4130
Grade 8 and 4130 are in no way similar. Grade 8 is a condition, 4130 is a steel alloy.

If you want another spec, provide the information i asked for, and i will "guess" whether it might be possible, and whether to keep doing your development work for you. Even if you spec "4130" you need to state the condition.

You should also sketch the form for heading the hollow rivets, with dimensions or reference to define the curve. The weak point in my speculative option is the stem diameter of the lower die. The shape of the curve and the material the hollow rivet is to be made of will determine force required.

smt
 
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