Rivnut weight capacity

[02rangeredge]

alright guys, I have an aluminium truck cap in need of some reinforcement ribs for a ladder rack and was going back and forth between nuts and bolts and rivnuts to fasten in these ribs since I don't have the time or resources to weld the aluminium ribs in- this rack is going to carry 2 kayaks so roughly 90 lbs not a rtt. So that said would rivnuts be able to carry 90 lbs at 70-80 mph? or are nuts and bolts my only option?

 

[Ducky's Dad]

Will depend on the rivnuts. Big ones will be plenty strong, probably stronger than the shell, but can be a real pain to install if you can't get a good angle on the tool. If you are using a manual puller, you can cheat by adding a length of pipe to the handles to increase leverage. I used 1/4" rivnuts to reinforce the nerf step mounts on my truck after I got stuck and bent things a bit. Mounts now appear to be strong enough to support the 8500-pound truck in a pinch. Your mounts will probably be loaded in shear rather than tension, so should be OK if you distribute the load. But don't rely on my opinion.

 

[BPD53]

Just an example. I used 3 stainless 1/4x20 rivnuts to secure my auxiliary fuel cell in the bed of my truck. The cell holds up to 35 gallons. The fuel cell weighs roughly 225 pounds when full. I have been at some pretty crazy angles off road with fuel in the tank and have had zero issues.

I have faith in my rivnuts, but I used a quality tool for installation. I also like stainless rivnuts for rust issues.

I have several rivnuts on my truck and countless rivets with no issues yet.

 

[02rangeredge]

Will depend on the rivnuts. Big ones will be plenty strong, probably stronger than the shell, but can be a real pain to install if you can't get a good angle on the tool. If you are using a manual puller, you can cheat by adding a length of pipe to the handles to increase leverage. I used 1/4" rivnuts to reinforce the nerf step mounts on my truck after I got stuck and bent things a bit. Mounts now appear to be strong enough to support the 8500-pound truck in a pinch. Your mounts will probably be loaded in shear rather than tension, so should be OK if you distribute the load. But don't rely on my opinion.

I was thinking I'd try to have the legs of the rack span across the width of the cap's original 1 inch aluminium tube ribs to try to prevent flex of the added cross members

 

[02rangeredge]

thanks for the tip, I'll probably choose stainless in case the rack carried any more weight than planned I don't want my fasteners to be my weak point

I honestly wasn't aware rivnuts came in various materials- I'm just planning out this modification right now, it'll have a few weeks before everything is planned/researched/ordered

 

[BPD53]

If I was going through the roof of anything I would use stainless closed end rivet nuts. The closed end should help with leaks. I even think they make rivnuts with gaskets on the outer flange?

The only problem I found with stainless rivet nuts is you usually have to buy a bulk pack. You end up with enough to last a while. I had to buy a bunch because of the different thicknesses of metal I was working with at the time. They categorize them according to material thickness among other things.

 

[02rangeredge]

If I was going through the roof of anything I would use stainless closed end rivet nuts. The closed end should help with leaks. I even think they make rivnuts with gaskets on the outer flange?

The only problem I found with stainless rivet nuts is you usually have to buy a bulk pack. You end up with enough to last a while. I had to buy a bunch because of the different thicknesses of metal I was working with at the time. They categorize them according to material thickness among other things.

thanks, I'll start reading up and try to find my material thicknesses- any knowledge is a new knowledge at this point since I'm early in my planning stages

 

[Ducky's Dad]

I use only stainless on my truck because it's stronger than aluminum, but not as strong as carbon steel. I always use anti-seize on stainless threads because stainless has a tendency to gall, and once it does, you are pretty much screwed if the stainless is stronger than your aluminum shell.

 

[rayra]

Problem won't be the rivnuts, it will be the thin metal of the shell. I think you'd do better to have an interior strip that matches the exterior and thru bolting things so the cap skin is sandwiched between them. You're planning to penetrate the roof anyway.

 

[javajoe79]

You might consider wide flat feet for the rack and glue it down with Sikaflex. That will spread the load, not put holes in the skin of the capper and be plenty strong if you have enough surface area to glue to. Or build a rack with attachment points that mount between the bed rail and the capper. Run bars up, across the capper and down to the other bed rail.

 

[02rangeredge]

Problem won't be the rivnuts, it will be the thin metal of the shell. I think you'd do better to have an interior strip that matches the exterior and thru bolting things so the cap skin is sandwiched between them. You're planning to penetrate the roof anyway.

I'm only penetrating the thin metal skin a few times, maybe 6, and it's going to be straight to about 1/4 inch of aluminium bracing I've spent a lot of time thinking over the weaknesses of that skin so any penetrating of it will also penetrate a brace-also rivnuts was not actually what I've decided to use are wide flange blind rivets

 

[02rangeredge]

You might consider wide flat feet for the rack and glue it down with Sikaflex. That will spread the load, not put holes in the skin of the capper and be plenty strong if you have enough surface area to glue to. Or build a rack with attachment points that mount between the bed rail and the capper. Run bars up, across the capper and down to the other bed rail.

the cap itself isn't designed in a way that glueing the feet would allow the rack to be fully supported and as far as your second idea there, I just don't have the fabbing skills to join materials at those angles (I can't weld sadly) and the way I've laid out to add the ribs will actually increase the strength of the cap

 

[javajoe79]

Ok cool. Can you take some pics and post them? I'm not sure I am envisioning what you have to work with

 

[02rangeredge]

Ok cool. Can you take some pics and post them? I'm not sure I am envisioning what you have to work with

It's just a standard light duty aluminum truck cap/topper made of super thin sheet metal and 1x1 square tubing with four ribs spanning width wise across the yft bed, I'm taking .125 in 1x2 to run 2 braces between each rib, a . 125 plate will sandwich the rib extending 3 inches down each brace, 4 as wide flange blind rivets will go into each brace at each end, primarily done before sliding the braces in between the ribs, making so only about a third of the top side rivets pierce the shell, the bottom halves of the saving will be identical to the top plates, a few screws from below will hold the bottom plates to the ribs, the feet of my rack are 1x2 so depending on mounting location the will either straddle a factory rib going through the brace and plates or simply go through my brace and plates behind the rib, running the bolts for the rack through thicker aluminum than the cap framework is constructed from, again, the rack isn't going to be hauling wait all of the time it is simply to transport 90 lbs of kayaks to and from the river

 

[javajoe79]

Sounds good