Quote:
Originally Posted by SerpentEagle
Thanks for the rules of thumb, they will definitely come in handy.
Im not actually going through both walls of the tube, just the one on the inside. Is this a bad thing?
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Going through only one wall of the tube is a good thing assuming that you can actually get tools in there to tighten the fastener.
Keep in mind everything is relative. A lot of it depends on the type and magnitude of the loads that will be seen on that part.
For example tapping a piece of 1/8" wall tubing for a #10 bolt will result in a far lower strength that the bolt is capable of. However it may still far exceed the loading requirements for a given application. For example if you were using that to mount say an encoder or a motor controller you would still have more than the strength needed for the job.
The same thing applies for going through both walls of a tube. A low applied force means that you could stop before the tube starts crushing and have more than adequate strength.
The relative strength of the materials also is a factor. Use a grade 8 5/16" bolt to go through a 1/16" wall tube and you'll certainly be able to crush to tube flat. On the other hand use an ungraded #6 bolt to go through 1/4" wall tube and the fastener will probably fail well before you could do any crushing of the tube.
For applications like the one in your picture where the fastener is at the end of a tube I like cutting the end of the tube at an angle when it doesn't affect anything. That makes it easier to put a tool on the fastener and to get the fastener installed.