Rivets vs threaded fasteners

[ToddF]

This post is spurred by a conversation with a student yesterday. He suggested that we use rivets instead of #10-32 fasteners to attach a critical piece of structure. My first reaction was negative, but I found myself unable to articulate a truly good explanation why we should use fasteners over rivets. As an engineer, that's not acceptable, and is a sign that I've got some unjustifiable biases in my thinking.

Would anyone be willing to share their engineering based opinions about the pros and cons of using rivets vs threaded fasteners in FIRST robots? Are there certain applications where your team prefers one type over another? Do you have certain design rules, tools, specific rivet part numbers, etc. which you use successfully? Would you, for example, use rivets to attach a plate sprocket to a versahub? Why or why not?

We've used rivets sporadically in the past, but it always seems that by the end of competition season, many, if not all of them have been drilled out and replaced with threaded fasteners. Rivets are used quite successfully in the industrial world, on a wide variety of applications, so I suspect that we are just using them wrong.

Here are my observations based on past experience. Please correct my mistaken beliefs if your experience says I'm wrong:
- If parts need to be removed for servicing the robot, you should use threaded fasteners. Rivets should be used for installations which are expected to be permanent.
- Rivets are best in shear applications. If used in tension applications, they tend to loosen up over time, and aren't easily re-tightened except by drilling out and replacing the rivet.
- Rivets of similar strength to threaded fasteners (tension and shear) don't offer significant weight savings. Corollary: Replacing a threaded fastener with a lighter rivet results in reduced strength in that joint. (The exception may be if use of a rivet results in the elimination of a nut)
- Rivets are most useful and have the most potential for weight savings when joining very thin materials (ex 1/16" thick aluminum) which can't be tapped.
- When riveting soft materials, like lexan, the head of the rivet must be against the soft material, or a close fitting washer must be used on the "bulb" side, so the bulb doesn't pull into the soft material.

Anyone care to share their experiences? I'm hoping for more detailed responses than "We use rivets. They work great for us." How do you use them? What do you do to make them work for you?