Buying SHS and RHS Steel.

[birchy]

How about using a thinner wall and reinforcing with either plates or tubes inside the box? The tubes go across the inside faces to prevent the walls collapsing when you tighten the bolts...

[Wal]

Well, that's an option, I guess, but it'll probably be quicker and less hassle to bite the bullet and just drive down and collect the section I want - positioning a plate or a tube deep inside box section sounds like a bit of a ball-ache - especially as it'll have to be a tight fit for it's intended purpose (bracing the walls).

Cheers.

Wal.

[birchy]

Normal practice with the tubes is to saw them to about 0.5mm undersize a tack weld them inside the box. Obviously you can't do that if your holes are not near the ends of the box.

[Wal]

Cheers for that info.

Chances are that it's academic in this case, as the bolts are going through and into (threaded) adjacent walls as opposed to through the entire cross-section, so it's really more a case of thread engagement and being able to apply torque without distorting the walls of the box that are joined. Hence the 6mm.

Thanks for your advice.

Wal.

[GEOFFREY]

If using thinner wall box, you can drill right through enlarge the bottom hole to allow the tube to pass through end extend at the bottom by say 5mm. Bolt up (long bolts) very tightly and then weld the tube extensions to the underside. The use of lighter tubes would certainly make any future move easier. G.

[birchy]

In my honest opinion, I think that 6mm wall thickness on those lengths is way OTT. You'd have to use something like M16 or M20 bolts to match the shear strength of those sections. It is generally poor design to pass a bolt through a box section as it will crush the walls unless you use reinforcing tubes as suggested earlier. The next option is to drill a clearance hole in one face and use short caphead bolts and nuts so that you're tightening face to face rather than across the section. If you insist on having threads in the box section, you could also weld a nut or threaded block inside the box section. Or you could use rivet nuts: How to install a rivet nut (rivnut) and the tools you need - YouTube

[Wal]

>The next option is to drill a clearance hole in one face and use short caphead bolts and nuts so that you're tightening face to face rather than across the section.

Indeed, that was the plan all along - fastening the adjacent walls together without having to compress across the section (hence no need for the tubes).

I did wonder how we all got onto the tubes...

Cheers!