Blind rivets

[theoldwizard1]

I have a project where two pieces of material will be blind riveted together. The load will be almost 100% shear and I will use 2 rivets. It has been awhile since I have riveted anything, so this question may sound stupid !

When the mandrel breaks off, does it break off flush with the dome or does it break off closer to the bottom ? I want that little bit of extra length to help prevent the rivet from shearing. I would love to use a backing washer, but it is truly a "blind" installation.

 

[mrolds88]

It varies a bit from size to size and rivet body materials. Larger rivet will be stronger. 3 most common body materials include aluminum (softest), Steel, and Stainless steel. If you're worried about it even further, you could drill the rivet after installation and drive in a bit of drill rod or regular round stock. Just drill out as minimally as possible.

 

[The Cobbler]

I think the steel rivet with steel mandrel usually break at the head, alum rivet & steel mandrel pull through.
what size rivet are you using? could you run a self tapping screw through the mandrel?

 

[hawkeye2]

Install a rivnut then put a screw in. Looks like they’re available in 6-32 and up.

 

[Jerm]

http://www.cherryaerospace.com/product/cherrymax

I use those in aviation almost everyday.

 

[rlitman]

http://www.cherryaerospace.com/product/cherrymax

I use those in aviation almost everyday.

+1. The cherry is what you want for this sort of shear use. On the cherry, the stem is integral to the strength, unlike most pop rivets where it does little to nothing.

 

[MFolks]

Cherry,are good rivets,strong,but need to be installed correctly,grip length is important.

 

[MoonRise]

Specific application?

Shear load analysis has to consider not just the failure of the rivet, but also the failure of the plate/sheet via several possible failure modes.

And making the joint as a double-shear configuration is 'better' than a single-shear lap joint, if at all possible.

Quick rule of thumb is to not place the rivet (or a bolt/screw) closer to the edge of the plate/sheet than 1.5 x the fastener diameter.

And +9 on use a bigger diameter rivet and a stronger material to get a 'stronger' rivet.

 

[joe49]

Just pull tight and stop short of the pop. Remove rivet tool, then cut and dress stem as you like.

 

[rlitman]

Just pull tight and stop short of the pop. Remove rivet tool, then cut and dress stem as you like.

That doesn't help.

For starters, the stem is grooved to snap, and will snap in shear if you just leave that piece in.

Next, the stem is designed to pull freely out, and at the surface of the rivet is a slip fit (the wide part at the back doesn't extend that far forward), so it does not provide any help to the rivet in shear.

If you really want to re-invent the wheel, you could pop the rivet entirely, knock the stem in with a punch, and then drive in a taper pin (or, I suppose, a spring roll pin). But none of this is superior to a Cherry that's made already for this exact purpose (and yes, with a Cherry, grip length must be selected properly).

 

[joe49]

Did you miss the original post? I missed space craft or aircraft mentioned. I did notice he wanted to try to leave the stem in order to maybe gain some extra shear.

 

[Jerm]

I use cherrys outside of aviation, partially due to my ability to get them easy. The stem stays in a Cherry rivet and it breaks off flush with the head which also engages the lock ring at the top of the rivet head. They could be over kill for the application, with knowing the material thickness the proper grip length could be gotten. There are probably a dozen other fasteners that could be used, they were just a suggestion.

 

[4xdog]

Probably an application for a “structural blind rivet”. The Hanson Rivet site has lots of useful information and all kinds of products. Good mail order service. Two rivets is kind of inefficient to buy from them, though...

 

[theoldwizard1]

I use cherrys outside of aviation, partially due to my ability to get them easy. The stem stays in a Cherry rivet and it breaks off flush with the head which also engages the lock ring at the top of the rivet head. They could be over kill for the application, with knowing the material thickness the proper grip length could be gotten.

CherryMAX Rivets sounds like what I want ! I ASSUME the 1/8" diameter MONEL rivets can be "popped" with a standard rivet gun, yes ?

The material is 0.0625" thick stainless tube. The outer tube is 1" OD and the inner tube is 7/8" (0.8750") OD. Yes, there this will likely be an interference fit, but I am hoping that heating the outer and cooling the inner will allow them to slip together and then holes can be drilled for the rivets.

 

[Jerm]

With only doing a few rivers, you should be able to do them with a hand puller. The grip length on two pieces at that thickness should be a (-2). You will want to make sure that the holes are burr free, cause cherrys do not like rough holes.

 

[MoonRise]

How about some 3/16" diameter stainless steel interlock rivets?

Grip range of 1/16" to 1/4", so your tube thickness is right in range.

1300 lb rated shear strength. So if your 'small' tube is loaded in tension (thus loading the rivets in shear), you'd need about six rivets to equal the tensile strength of the stainless tubing (assumption of 50 ksi tensile yield strength of the 7/8" OD stainless tube). That's with NO Safety Factor added.

Order a few more than just your two that you plan on using though, just in case a 'pull' doesn't go right.

$0.63 each, if ordering individually.

https://www.boltdepot.com/Blind_riv...ess_steel_18-8_-_Stainless_steel_mandrel.aspx

You might have trouble setting them with a 'standard' Pop Rivet tool.

If you go up to the 1/4" diameter stainless steel interlock rivets, they have a rated shear strength of 2400 lbs. So you could match the strength of the tubing with just 4 of the 1/4" rivets (well, 3.3 but you have to round up ).

$0.95 each, when ordered individually.

You will NOT be setting the 1/4" stainless rivets with a handheld Pop Rivet tool though.

https://www.boltdepot.com/Product-Details.aspx?product=15416

 

[metlmunchr]

If you're able to shrink those 2 tubes together with .005" interference as you talked about in a different thread, there's no need to worry about any rivets as they ain't coming apart with anything short of some sort of cutting tool like a lathe or splitting the OD with a cutoff wheel.

 

[joe49]

Couple of holes on in the outer piece and little silver solder or braze would take care of the shear.

 

[rick carpenter]

How is shear strength figured for multiple rivet applications? I want to rivet two small plates on each side of my truck bed's sheet metal rear cross member. If I use 4 blind rivets with shear strengths of -- for instance -- 160 lbs each, will the finished shear strength be as simple as 4 x 160 = 640 lbs?

 

[rlitman]

How is shear strength figured for multiple rivet applications? I want to rivet two small plates on each side of my truck bed's sheet metal rear cross member. If I use 4 blind rivets with shear strengths of -- for instance -- 160 lbs each, will the finished shear strength be as simple as 4 x 160 = 640 lbs?

That depends on how the force is applied. A torque can work one rivet against another for example.

 

[rick carpenter]

I'm talking about shear strength only, no torquing or tensile forces will be applied.

 

[Jacko264]

Depending on the size of rivet you need there is rivets called mono bolts they look like pop rivets you will need a mono bolt gun to use them