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Question. What non-welding options do I have to reliably attach square aluminium tubes to an aluminium frame?

Context. This will be used for outdoor environment (gate). I'm thinking of non-welding options to attach horizontal square aluminium tubes to an aluminium frame.

The frame is welded. But I'd like the tubes to not be welded.

My reason is that I think that replacing non-welded aluminium square tubes is easier than re-welding. Because, repairing welds will require to repaint the door, including other areas near the weld, even parts not relating to the damaged part. On the other hand, if the square tubes are attached in a non-welding way, I can only replace the damaged square tubes, without needing to repaint anything nearby.


Appendix. I'm trying to achieve this look using square aluminium tubes.

enter image description here

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    $\begingroup$ What about fasteners or riveting? $\endgroup$
    – NMech
    Oct 16 at 13:20
  • $\begingroup$ @NMech - Applicable. Is riveting more reliable for outdoor use than fasteners? $\endgroup$
    – caveman
    Oct 16 at 13:34
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    $\begingroup$ Any fastener will work loose over time. $\endgroup$
    – Solar Mike
    Oct 16 at 14:59
  • $\begingroup$ sheet metal screws (carefully chosen for the aluminum thickness) + sealant? be aware that aluminum + steel + outdoor = galvanic corrosion $\endgroup$
    – Pete W
    Oct 16 at 17:36
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I've constructed a couple of square aluminum tubing "structures," of relatively small overall size, but subjected to forces applicable to this project.

Rivets will indeed loosen, but combining an adhesive such as epoxy with rivets will provide for durability. Should replacement be required, drilling out the rivet will allow a hammer blow to release the epoxy.

That method was successful for one project, but for another, I used rivnuts and bolts.

rivnut image

I had to drill "access holes" in the bolt-side tubing, as I wanted the bolt heads to be within the tubing. If one is going to use a full length through-bolt, one would want an inner bushing/sleeve to transfer the load from the head of the bolt to the inner tubing wall and prevent crushing of the tubing.

Installation of the rivnut should be done correctly. As noted in the linked article below, oversize holes are problematic. Stripping the internal threads is easily done with aluminum inserts.

failed rivnut

The images are from the linked site. The image above appears to have been the result of an oversize hole, as the bulbed part of the rivnut is flush with the underside of the head. Another aspect of the linked article is the suggestion to use the correct tools. With a project of this size (fence/gate), it is a wise suggestion.

In researching for photos for this answer, I found a website that references both rivnuts and plus-nuts, a product of which I was unaware until now.

plus-nut image

It's easy to see why this product is called a plus-nut. More expensive, but with greater holding power, according to the linked article. The article suggests that it is more tolerant of oversize holes, but that falls back to the "use the right tool" reference.

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The only reliable way to make a tube-to-tube connection is using a "thru-bolt", it is removable but aesthetically unpleasant. "Blind bolts" can be considered for the tube-plate connection, but you might damage the base material while trying to remove it.

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