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Posted by D Sherman [72.47.9.228] on Friday, April 29, 2011 at 19:26:36 :
In Reply to: Why rivets in cross frame members???? posted by Doinco [68.177.210.80] on Friday, April 29, 2011 at 18:47:17 :
The reasons usually offered are:
1) No chance they'll work loose.
2) Cheaper to install in the factory.
3) Can work with misaligned holes.
4) Fill the holes completely thus providing greater load-bearing area.
I think we tend to gloss over the importance of #4 these days.
Rivets are rarely used these days and so we think of them as exotic, but 50 years ago they were still the common way of attaching structural steel in bridges and buildings. Most rivets in structural work have been replaced by welding, with bolts used in the rare places where field welding would be impossible or impractical. To get maximum strength with finished bolts, you need to drill or punch the holes under-sized, clamp the parts together, and then ream them to a close fit with the bolts. With anything less than that, the bolt will bear on only a small part of the hole, which will deform until sufficient bearing area is obtained to carry the load. If the joint can slip at all, and the load changes direction from time to time, the result is a "wallered out" hole. With rivets, on the other hand, the rivet automatically expands to completely fill misaligned, rough, or over-sized holes.
Well-fitted high-strength bolts would probably be fine here, since the parts are over-built anyway, and rivets may only have been used because installation was cheaper. The main thing is to make sure the holes are drilled to finish size together so they fit the bolt as snugly as possible. And of course use a bolt whose shank is exactly as long as the thickness of the frame members, since the threaded part has very little bearing area. A heavy lock washer helps with the transition.
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