Thread: Buying SHS and RHS Steel.
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.
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.
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
>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...
Ermmm...so that brings us back to the beginning...why do you need such thick wall box sections? Is the frame going to be supporting several tonnes?
Heh, no, you're right. I'm not going to be supporting a great deal of weight. To re-cap:
The frame needs to be built in situ (in my cellar) and will at some point in the future need to be dismantled, so - welding is not really an option.
Bolting it together is very much an option. To avoid issues with rigidity and to give me a reasonably good starting point in getting the frame square, I have decided to build a squat floor level frame (as in the animation at the top of the thread). This means I'm using less metal, but I still need the frame to have a fair bit of heft to it. In it's current theoretical spec the frame alone weighs 110Kg. That's not super heavy, but it's also not that light. A reasonable compromise, I'd say. Using 6mm wall box section not only adds to the weight of the frame, but it also means that I'll have an ample 6mm of thread for the holes that I'll tap. That, to me, is important.
Yes, I could use a screw and a nut through oversized holes, rather than tap into the box, but for now I'm favouring the former (threaded) approach with the screw passing through an oversized clearance hole.
Because box section has a slight curvature across it's profile (exaggerated in the pic below) using section with a thinner wall there'd be more of a danger of distorting it when torquing up the screws - 6mm wall will help to mitigate this.
So while I am over-engineering this a bit, it's for the right reasons: weight and rigidity.
Anyway, it's all drifted a bit off-topic, I just wanted to buy some hollow section steel...!
Seriously, thanks for your posts and advice - it's all really helpful, but I have thought long and hard (well, for my pea-brain) about this, and I'm at the stage of having to go with the courage of my convictions.
(Guaranteed if I changed my mind to 4mm then someone would be along sucking their teeth and telling me how badly it's going to deflect and knock the earth off its axis etc...)
I've been planning this build for well over a year and I still haven't got a frame. It's embarrassing me now.
Ok, no problem. I was only suggesting alternatives as you seemed to be making hard work of a simple job. I guess you could partially weld the frame and bolt the sections together but I can see that you have your heart set on bolting everything. Your best bet for the steel is to spend half an hour on the phone to those local companies I linked to earlier. You'll get something local as most of the steel manufacturers are 'oop North anyway.
I'm planning on fitting most parts with a 'chemical metal' filling the gap. Once dried it should easily take the compressive load and allow for slight alignment errors.
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