Hi,
My team is working on a practice chassis during the off season using 1/8" sheet metal. To hold it together, we are use 1/4" diameter rivets. Does anyone have any suggestions as to how far apart the rivets should be placed?
Luke,
What type of metal and rivets are you using? Also, where in the frame are you looking to use the rivets? Different frames will distribute the loads through the rivets that are holding it together differently. 1/4" diameter rivets sounds like a bit of overkill to me. It was hard to pull our 3/16 rivets with the hand tools we had, and 1/4 would be even harder. The maximum size rivets we have used were 3/16" rivets, and they had something like 400 lbs of sheer and tensile strength. We typically use 1/8" rivets for medium strength stuff, and 3/16 rivets where we need strength.
While this won’t answer your question exactly, you can look up the sheer and tensile forces that the rivet can withstand on McMaster or wherever you bought the rivets and use that to determine what you need. A quick search on McMaster found a variety of strengths, but, for example, 98780A412 has a sheer strength of 2450 lbs and a tensile strength of 2250 lbs. Which shows that at least that rivet can withstand a heck of a lot of force, and you won’t need very many of them to hold something together.
Hopefully someone else can weigh in on what they would recommend as well.
Having used 1/4" Rivets on a chassis before, I have to confirm that they are probably overkill for your application. However, a proper physical analysis of the expected loads on your frame is the only way that you can fully confirm what you should be using, where, and how much.
If you want a point to start from, I would suggest a quick look at the design of the old IFI Kitbot, as people have reported success in the past rivetting them up.
Or put another way: Use as many as you think you need so it doesn’t fail.
Rivets are pretty strong, probably more so than the material being riveted. If I were building a bumper frame around my robot, I’d use rivets only in the corners where I need to join metal. If I wanted to hold 2 long pieces of metal together, I might use a rivet every foot or two and see what happens.
But the real answer is what ,4lex S. wrote: Analyze (aka “Do The Math”)
Keep in mind that designing to the rivet’s failure tensile or shear strength isn’t the only thing to consider. Typically, inter-rivet buckling is a dominant failure mode. That is, the material between rivets has enough room to buckle (bend out of plane). Sometimes that’s OK, but this is why smaller rivets are typically used with closer spacing.
For airplanes we keep the pitch (distance between) about 4 to 8 times the diameter and reduce the diameter until the total load carrying capability is just met. Though our loading is less impact dominated than FRC.
or so we hope!
3/16" rivets may be a better as it is cheaper and easier to get the rivets and tooling needed and are plenty strong enough when used correctly.