fastening to aluminum square tubing

dman93

Adventurer
I hate to respond with another question, but you guys are provoking me to thought!

Q: unless it's a degree in engineering conclusion, how would one determine "tight enough". I have a 1/4" drive torque wrench (which I rarely use) I bought for bike repairs, but unless i'm given the setting to torque, is there a general 'rule of thumb' table somewhere?

for example: Joe wants to attach 1/8" aluminum to 1/8" aluminum with nutserted #8 x 32 tpi x 3/8" RH machine screws.

Q: what is the distance between fasteners and what should the torque (inch pound ???) of the fasteners be?

or is this getting a bit out of hand and I need to be reeled in?
The torque for a #8 fastener is so low that just a few variables can throw things off, so honestly, just snuged up is probably the best engineering answer. As for for how many fasteners or distance between, that is easier to calculate but depends on the magnitude and direction of the load, as well as the geometry of the assembly. A light load in tension or shear could get away with one fastener. That’s what you hold your pants up with. Where the assembly needs to resist rotation, you need at least two fasteners, as far apart as possible. If the load is say 2x the working limit of one fastener, you should probably use 4 fasteners (factor of safety). Etc ...
 

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