2

I have an enclosed cargo trailer. I need to install some rivnuts in the roof beams from the outside of the trailer. The aluminum skin of the trailer is attached to the steel tubing framework using some sort of adhesive. The result is that the aluminum is not directly against the steel tube. When the rivnut is installed, the deformed part of the rivnut ends up between the aluminum skin and the steel tube instead of inside the steel tube. This results is a much weaker anchor.

The following pictures shows the problem:

enter image description here

These are three different cross section drawings. Looking at the left one you can see the aluminum skin on top and the 1" wide x 1.25" tall steel tube. Between them is the layer of adhesive. I have no access to the underside of the steel tubing (which is why I am trying to use rivnuts in the first place). Removing the adhesive is not an option for several different reasons.

The rivnut is just placed into the hole in the left cross section.

The middle cross section is the result I am getting after compressing the rivnut in place. Note the compression is happening where the adhesive is.

The right cross section is the result I wish to get with the compression inside the steel tube.

The tool I'm using to install and compress the rivnut is little more than a big nut on a grade 5 bolt.

How can get the rivnut to install as shown in the right-most cross section shown in the picture? Would a different/better tool work?

The nut on my installation tool has a slight lip on it about the same height as the flange on the rivnut. It seems that if the nut had a taller lip on it (the same as the thickness of the aluminum skin, the adhesive, and the wall thickness of the tubing) then it might work.

8
  • Are you sure you're drilling the right size hole for the rivnut? I can imagine what you describe happening if the hole is a little too large. – brhans Feb 27 at 4:40
  • The hole seems to be the correct size. The rivnut needed to be pushed into the hole ever so slightly. – rmaddy Feb 27 at 5:36
  • This problem makes that quarter-twenty-eight tap look a bit more attractive. – fred_dot_u Feb 27 at 10:48
  • @fred_dot_u , what’s the comment about 1/4-28 tap? Rivnuts are threaded inserts used where the metal is thin or in some cases two soft. The only place I use 1/4-28 is on ar15 pistol grip screws, just wondering? When I install rivnuts I want a very tight fit, maintains downward pressure on the skin I have tied 2 layers of metal to the aluminum frame on my van for mounting ladder racks in the past. – Ed Beal Feb 27 at 14:48
  • 1
    @EdBeal They are most likely referring to a related question (engineering.stackexchange.com/questions/40430/…) I posted earlier. – rmaddy Feb 27 at 16:05
1

You need a longer rivnut where the compressive section is further away from the head.

Or remove the adhesive layer and then the rivnut will work correctly .

4
  • The grip range on the rivnuts I have are 0.027" - 0.165". The distance from the outside of the aluminum skin to the inside of the steel tube is within that range but it is close to the max. I supposed I could by a set with the next higher grip range and see if that helps. Removing the adhesive is not an option for several reasons. Thanks. – rmaddy Feb 27 at 6:38
  • Because the expansive section is mostly with the metal parts as you have just explained is why it does not work. There are only two options: Get longer ones or change something. – Solar Mike Feb 27 at 6:46
  • Thanks. I'm going to try a better tool and different rivet nuts. It will be a couple of weeks before I can get and test the new setup. I'll update when I can. – rmaddy Feb 27 at 16:28
  • Using a rivnut with a longer grip range solved the issue. I also got a better tool as shown in the answer by @Michael Karas. That definitely made it easier to install. But the longer grip in the rivnut allowed the rivnut to form in the correct location. – rmaddy Mar 6 at 5:45
2

I think that part of your problem is your use of the super economy installation tool. With that kind of tool it is difficult to hold the rivet nut very firmly into the hole.

I use this type tool for installing rivet nuts and have had good luck with its use. The tool allows you to press down firmly on the rivet nut while at the same time folding the handles together to compress the rivet nut.

enter image description here

Picture Source

Rivet nuts are designed to allow crimping into materials in a certain range of thicknesses. They do require a hole through solid material that is a snug fit with the body of the uncompressed rivet nut. It is quite possible that you will never achieve a satisfactory result with the soft adhesive material between the outer skin and the metal tubing. One thing that you may want to try, after obtaining a better installation tool, is to heat up the area surrounding the installation site for a four or five inch area to soften the adhesive. Then with the better tool you may be able to compress the softened adhesive a bit when pressing hard down on the compression tool.

2
  • Thanks. I'm going to try a better tool and different rivet nuts. It will be a couple of weeks before I can get and test the new setup. I'll update when I can. – rmaddy Feb 27 at 16:28
  • I ended up getting a better tool very similar to that shown in this answer. That made it much easier to install the rivnut. But the key, for my setup, was to use a longer rivnut with a more appropriate grip range. With the proper rivnut and a better tool I was able to get a proper install without having to do anything special with the adhesive between the two pieces of metal. – rmaddy Mar 6 at 5:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.