Quote:
Originally Posted by ToddF
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.
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Threaded fasteners do make removal and replacement a bit easier. If you know you need to remove a part to service it (or another part) then use threaded fasteners.
Quote:
Originally Posted by ToddF
- 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.
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Not quite true. Screws in tension have stress risers at the threads which can cause the thread to fail. Threaded fasteners tend to loosen due to vibration. Rivets tend to loosen because they are incorrectly sized (reach is wrong or hole size is wrong). Rivets only loosen in tension if there is a shock load on them. So if you expect a lot of vibration, use rivets. If you expect heavy shock loads, use threaded fasteners (with Loctite).
Quote:
Originally Posted by ToddF
- 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)
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Most threaded fasteners are hardened steel. Most rivets are aluminum. For the same strength the rivet will typically weigh 2/3 the weight of screws.
Quote:
Originally Posted by ToddF
- 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.
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Rivets tend to be useful on thin material for that reason as long as the reach of the rivet is correct, however, rivets also save weight when the strength of steel screws are not needed and nuts can be removed.
Quote:
Originally Posted by ToddF
- 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.
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The same is true for screws. Soft material should always have washers to spread the load of the fastener (regardless of type).
Hope that helps.