Rivet bucking question

[spaceflightmeow]

I'm confused about how the shop head is formed when a rivet is driven with the rivet gun on the manufactured head side. Does the process rely on the surrounding sheet deflecting in order to transfer impact momentum to the bucking bar? Say the rivet is dropped into a countersunk hole and sits flush. Since it can't be displaced any further, the rivet gun blows to the head cannot transfer momentum to the bucking bar unless the surrounding sheet deflects as well. Isn't that risky since you are bending the sheet and potentially making smilies?

This video by Disney on riveting raised the question:
http://youtu.be/dyXEjn7f330?t=9m30s

You see the rivet gun stationary on the manufactured head, holding the rivet in the countersunk hole, and the bucking bar striking the rivet from the bottom to form the shop head. Seems like it would be the opposite way around.


Back-riveting makes more sense to me. The rivet sits flush in the skin and a steel plate backs up both the skin and the rivet. The rivet gun then bangs on the shop head side and strikes ONLY the rivet, transferring momentum directly into the rivet rather than relying on skin deflection.

[cfiidon]

Originally Posted by spaceflightmeow

I'm confused about how the shop head is formed when a rivet is driven with the rivet gun on the manufactured head side. Does the process rely on the surrounding sheet deflecting in order to transfer impact momentum to the bucking bar? Say the rivet is dropped into a countersunk hole and sits flush. Since it can't be displaced any further, the rivet gun blows to the head cannot transfer momentum to the bucking bar unless the surrounding sheet deflects as well. .

Not quite so. You are imparted momentum thru the rivet to the bucking bar. Think of the old desk top toy with 5 ball bearings suspended (Newton's Cradle). One ball hits the second, and the momentum is transferred to the last ball. This motion continues unabated for quite some time. It should be forever, but the real world induces losses.

See http://en.wikipedia.org/wiki/Momentum for more info, but fair warning, it's heavy in math, but the visualizations with the ball bearing and billiard balls "might" convince you..

Don

[spaceflightmeow]

Thanks, I guess that makes sense. I push electrons around in my day job so my intuition on mechanical things is rusty.

Incidentally I'm working my way through "Structures: Or Why Things Don't Fall Down" by J.E. Gordon, which offers an intuitive approach to understanding materials and mechanical concepts. It's an excellent book!

[Charles in SC]

I had a friend that was willing to help me with some of my two people rivet jobs but had never done it before. I set up some scrap pieces for us to work with and while doing this I found that it is helpful to set the rivet gun very slowly while you get the feel of it. Practice with a couple hundred rivets and draw your own conclusion. I am of the opinion that for good results the material being riveted together has to move enough to push the bucking bar. When this happens your hand holding the bar is pushed away and the metal and rivet flexes back as the rivet gun makes it's back stroke. Then the rivet gun starts it's next outward stroke at about the same time your hand with the bucking bar comes back in. The bar and rivet hit and the shop head forms as this happens over and over. Back riveting is different.
Hope this makes since!

[BillL]

Originally Posted by spaceflightmeow

I'm confused about how the shop head is formed when a rivet is driven with the rivet gun on the manufactured head side. Does the process rely on the surrounding sheet deflecting in order to transfer impact momentum to the bucking bar? Say the rivet is dropped into a countersunk hole and sits flush. Since it can't be displaced any further, the rivet gun blows to the head cannot transfer momentum to the bucking bar unless the surrounding sheet deflects as well. Isn't that risky since you are bending the sheet and potentially making smilies?

This video by Disney on riveting raised the question:
http://youtu.be/dyXEjn7f330?t=9m30s

You see the rivet gun stationary on the manufactured head, holding the rivet in the countersunk hole, and the bucking bar striking the rivet from the bottom to form the shop head. Seems like it would be the opposite way around.


Back-riveting makes more sense to me. The rivet sits flush in the skin and a steel plate backs up both the skin and the rivet. The rivet gun then bangs on the shop head side and strikes ONLY the rivet, transferring momentum directly into the rivet rather than relying on skin deflection.

Yes, the rivet and the structure move, although only a tiny amount. These structures are quite flexible. Even the swinging balls move, but maybe only 1 X 10^-6 " Strain energy has to be generated to transfer the momentum. It's not magic.

Don't worry about the physics, just learn to use the practical knowledge to properly set (drive) the rivets.

I just taught my neighbor to buck rivets yesterday. I sent the disney link to him and he found several more good youtube videos. There are some good vids there, watch them and experiment on your own.

[wjb]

Try using a tungsten bucking bar if you haven't .. the significant extra density over steel (about 2.4x) really makes a difference. That extra inertia in a small package makes for easy riveting!

If you want to see structure flex, try shooting a rivet with the bucking bar on the wrong rivet (no, I've never done this ;-). You get quite a bit of motion.

[BTW, my day job is to push electrons around, too, though I'm loving the mechanical stuff. Pro seal is way scarier that the whole of the electrical system]