Construction with gussets and bolts

[AdamHeard]

Originally Posted by Chris is me

If you end up using rivets again, for critical areas like a drive chassis, where you don't expect to ever be removing the rivets, high strength aluminum rivets stay very firm over time and are just as light as regular rivets. They aren't that difficult to remove if you have to - you just need to center punch the rivet hole as the mandrel tends to break flush with the top of the rivet, rather than slightly inside the rivet.

The other benefit of these pricier high strength rivets is that they are rated to work in holes going all the way up to .201". That way, you can cut holes to .196" or so and use a tight #10 bolt clearance hole that doubles as a rivet hole.

The extra cost of these rivets isn't insignificant though - http://www.mcmaster.com/#aluminum-rivets/=x9kpy0

We've ran regular 3/16" rives in .201 holes for years w/o issue (for anyone reading this and thinking you NEED high strength to handle the larger hole size).

[pfreivald]

If you insist on using bolts, consider these.

http://www.mcmaster.com/#standard-rivet-nuts/=x9l7zq

[Gregor]

Originally Posted by Nick Lawrence

One way that you can prevent the tube from being crushed is to press wood blocks into the center of thin wall tubing. This probably is not necessary for 1/8" wall tubing, but could be useful to make robust connections in 1/16" wall or thinner. I've attached a quick cross section below.

-Nick

The alternative to this is just proper training on not crushing tube. It's not worth the extra weight of putting in wood blocks or standoffs when the problem can be solved through training.

[AdamHeard]

Originally Posted by Gregor

The alternative to this is just proper training on not crushing tube. It's not worth the extra weight of putting in wood blocks or standoffs when the problem can be solved through training.

Yes and no.

By not crushing the tube (with no internal reinforcement) you limit the amount of preload and clamping force you are able to generate.

[Bennett548]

Adam is right.

Fasteners work best when they generate clamping forces high enough that the friction between the two parts being fastened is enough to keep the joint from moving. The bolt or rivet is never in danger of shearing or loosening because there is no movement in the joint.

That is why you should either put an aluminum spacer inside the tube, or figure out how to fasten the gusset plate to the tube wall itself. This is normally achieved with blind rivets. Rivnuts or small self tapping screws will also work.

[Mike Schreiber]

Originally Posted by Joseph Smith

If I understand correctly, this allows you to bolt thin sheet metal together without tapping?

Yes. Just press them in with an arbor press (gently) and make sure your material is stiff enough that when you clamp you don't locally deform the metal.

Originally Posted by Bennett548

Adam is right.

Fasteners work best when they generate clamping forces high enough that the friction between the two parts being fastened is enough to keep the joint from moving. The bolt or rivet is never in danger of shearing or loosening because there is no movement in the joint.

That is why you should either put an aluminum spacer inside the tube, or figure out how to fasten the gusset plate to the tube wall itself. This is normally achieved with blind rivets. Rivnuts or small self tapping screws will also work.

This is correct for bolts - the bolt loads the material it is clamping and the friction between these materials reacts shear loads. In FRC most chassis loads related to gussets or corners will be shear loads.

From my understanding of things, rivets are actually meant to be loaded mainly in shear, not tension.

[GeeTwo]

Originally Posted by Mr V

I have to agree with GeeToo that tapping 1/8" aluminum is not a good choice. The general rule of thumb is that for a hard material like steel the thickness of the tapped material should equal the diameter of the fastener. For soft materials with a hard bolt the thickness of the tapped material should be 2x the diameter.

Mr. V has most of the reason - too little thickness of too-soft metal. In addition to not having enough thickness for lathed or other fully-formed formed threads, There is the loss of strength which comes from a tapped thread. In order to use a tap (or die), you must give up some of the inner or outer surface of the thread, reducing all of the forces, shear, tensile and torque locking significantly.

Originally Posted by Mr V

In regards to the original question I prefer a bolt and nut through just the gusset and one wall of the tube. That does mean that the order of assembly must be considered and held to since if you are joining two tubes at right angles you will block access to one of the tubes with the other tube. This method will result in the ultimate strength since you'll have double the fasteners and often with less weight. Yes it is more difficult to assemble.

I concur that all of this is true. However, when our team has used gussets (actually steel flat angle braces), we have usually used gussets on both sides and through bolts for ease of assembly, at a slight loss of holding power. Since we were using C-channel in these cases, it can also be argued that we improved the torque resistance a bit more than if we'd used separate bolts on each face.

3946 has not used rivets for structural joints to date, but we plan to experiment with them this summer. The experiences I have read seem to indicate that we can do as well or better using several aluminum rivets with steel shanks where we used to use a single through hex bolt or cap screw and nylon locking nut. Still a bit of number crunching required to better define "several".

[Joseph Smith]

Thank you everyone for the helpful replies. I'm planning having my team do some testing this off-season to gauge how different fastening methods hold up to vibration, cyclic forces, shock forces, etc. Your responses have given me some new insights and ideas for other construction methods that are available. Thanks!