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My objective is to join 1"x1" aluminum tubes (80/20 Quick Frame: https://8020.net/9000.html) with external plates. Trying M5 screws, I discovered that tapping 0.06" aluminum sheet produces very fragile thread, which is easy to strip. Using #10 sheet metal screws with predrilled hole produced better strength, but still possible to strip with a screwdriver. What is the optimum screw size and a thread pitch to use on 0.06" aluminum sheet?

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    $\begingroup$ A pull rivet would be much stronger than any thread in this case. If you have to use a screw or bolt for future disassembly, use a threaded rivet on the tube then bolt the plate onto the rivet? $\endgroup$ Sep 12, 2022 at 13:37
  • $\begingroup$ Is torque out really a problem? A screw that's easy to torque out can still be very strong in tension and sheer. $\endgroup$
    – Drew
    Sep 13, 2022 at 9:14
  • $\begingroup$ @Drew The project will be disassembled, shipped and assembled by someone else. Stripped threads may still hold well, but the first impression is quite bad. $\endgroup$ Sep 14, 2022 at 16:21

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Have you considered a Thread Setter? (Reference: Marson Thread Setter kit) Drill a hole through your base, put in the thread setter insert, and crimp it down. Then you have a strong thread to attach your plate with. Just be sure to use a drill stop on your drill bit so that you don't accidentally drill all the way through your tubes.

This works very well for closers and hardware on sheet metal doors, also.

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  • $\begingroup$ Thank you. I didn't know about this kind of tool. They even have it in the store nearby: harborfreight.com/… $\endgroup$ Sep 11, 2022 at 20:28
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It is the material thickness that is the issue.

Consider using a backing nut to reduce the load on the thread in the thin material and also spread it over more area.

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    $\begingroup$ Unfortunately, the frame will be closed, so I won't have access to insert a backing nut. $\endgroup$ Sep 11, 2022 at 20:17
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I would think a welded nut is stronger. It depends on how strong it needs to be.

My second choice might be a SS fastener. It is recommended that the surface area of aluminum is larger than the stainless steel fasteners for corrosion reasons.

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