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.
Quote:
Originally Posted by Munchskull
When you machine 6063 Aluminum the chips tend to reform and stick on your end mills and other cutters.
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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".