Rivnut Tool

[GeeTwo]

The longer (.225") rivnuts arrived a couple of days ago, and I spent some time today in testing. I'm planning a white paper to be out before kickoff, but here's the gouge:

• I began by inserting the machine screw "dry", and tightening with a T-handle (I did not use arm strength; with limited hand strength, I can get to about 2 ft-lb with a T-handle). Unless that failed, I then disassembled the test unit, sprayed the threads with WD-40, and re-assembled for higher torque tests. All tests utilized new (or lightly stressed) stainless 10-32x1" allen-cap-head machine screws; I expect these to be a bit stronger and more consistent than "plain steel" machine screws.
• In 1/16" 6063 aluminum, I only tried the short rivnuts, because the longer ones would clearly not grip. The maximum torque supported with lubricated threads was 4 ft-lb, which theoretically corresponds to a clamp load of over 2200 pounds, which should have broken the machine screw. However, the failure mode was the rivnut pulling out of the aluminum through a "volcano" deformation.
• In 0.1" versaframe tubing (6061), the short rivnut performed sililarly to the 1/16" case above. The long rivnut secured tightly originally, and supported a torque of up to 6.5 ft-lb for several full revolutions. Failure was due to shearing of the machine screw near the head. After failure, there was definite visible deformation of the surface (~1/16"), and the rivnut was loose in the hole after failure of the screw.
• In 1/8" 6061-T5 C-channel, the short rivnut pulled out easily with about 2ft-lb of "dry" torque (provided by an Allen T-handle; torque estimated by hand). Note that in the preliminary test, I had applied far greater clamping force to the tool than should be required; in this case, I applied forces similar to those necessary to clamp in thinner material.
• In 1/8" 6061-T5 C-channel, the longer rivnut supported a maximum torque of about 6 to 6.5 ft lb. Failure was due to shearing of the machine screw, and there was no discernible deformation of the aluminum.
• In 1/8" 5052 plate (particularly, an AM-14U2 end plate), the behavior closely matched the 6061-T5 C-channel above in both cases.

Bottom line: Use the longer (.225) rivnuts in 0.1" and thicker material. TBD if a spacer or gusset will make mounts in VF thick wall tubing more secure.

Caveats: Due to budget limitations, we decided to try rivnuts this year in a very limited case. As we use 10-32 bolts for the majority of our structural work, this was the single thread we decided to experiment with this year.

Originally Posted by Munchskull

When you machine 6063 Aluminum the chips tend to reform and stick on your end mills and other cutters.

Thanks. I have noted that sometimes holes drilled in 6063 are not as large as the drill bit would indicate; I presume this is somehow related to "gumminess".

[Fusion_Clint]

Geetwo,

Help me understand your test. It seems that you are torquing the screw in the mounted rivnet to see when it will fail/stripout, is this the case?

Considering that the recommended torque for a typical 10X32 screw application is in the 30 In Lbs range, reaching from 48 to 80 In Lbs in most of the material is fairly impressive. http://www.federalscrewproducts.com/torque-chart.htm

[GeeTwo]

Originally Posted by Fusion_Clint

Geetwo,

Help me understand your test. It seems that you are torquing the screw in the mounted rivnet to see when it will fail/stripout, is this the case?

Considering that the recommended torque for a typical 10X32 screw application is in the 30 In Lbs range, reaching from 48 to 80 In Lbs in most of the material is fairly impressive. http://www.federalscrewproducts.com/torque-chart.htm

Yes. As described several posts above, I was using a 1/2" nut and three washers against the stock so that I was pulling on the rivnut, not simply tightening against the flange.

I had already noticed that the stainless machine screws supported several times the rated torque, even a good bit over grade 8. What I found even more impressive was that all of the shear failures occurred at the same torque to within about 10% (my measuring precision with this tool at that torque). Further the torque on the threaded portion was probably quite a bit less than the torque I was applying, due to friction between the head of the screw and the large washers.

[Forhire]

Testing is fun and you can learn a lot. Have you looked at the published ratings?
http://www.cardinalcomponents.com/as...properties.pdf

Like Clint mentioned fasteners under 1/4" will generally be measured in in/lbs rather than f/lbs.

Understand that the torque charts are a guide for a properly torqued fastener. These are within the working limits of the fastener. As you've discovered the shear point is quite a bit higher and material plays a big part.

I would think that if your seeing fastening system failures it is likely due to poorly designed joints and/or improper fastening system selection. Of course that's assuming proper installation.