tube / pipe fit over scaffold tube

Hello all
I've asked on a couple of newsgroup during the last month, but not their thing...
I want to find a tube / pipe, readily available, which will slide over
a scaffold tube. For making jigs and fittings from offcuts of scaffold tube.
Here in the UK (don't know about elsewhere), scaffold tube has 48.3mm outside diameter.
I did some web-searching and find, for example, that NPS 2 schedule 80, with 60.33mm outside diameter and 5.537mm wall thickness, should give 49.256mm bore.
Weld on "fins" with holes for bolts, slit between the "fins" and bolt-up, and the tube will contract and grip a scaffold tube???
Any knowledge on this?
Regards, Rich S
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Google 'scaffold tube fittings' and I think you will find what you need.
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Hiya Hope I am not missing something here, but there's stillages full of standard scaffold tube fittings here. No problem getting any number of those. It's tube to make custom fittings for the application of using offcuts of scaffold tube for purposes having nothing to do with scaffolding. eg. making rotating welding jigs which you can attach to your trestles for reliable neat series-run components. Scaffold tube is a "plastic section" (it's thick enough to never buckle in overload, only general bend) (???) so it's a very reliable structural member for improvised purposes, as well as being abundantly available. Regards, Rich Smith
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On 08/11/2019 05:59, Richard Smith wrote:

I'm still not entirely clear what you are looking for. If it is simply steel tube of a certain diameter then just search for it without mentioning scaffold.
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Clifford Coggin
Kent
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Whether or not a column of tubing can fail by buckling depends on its effective length to diameter ratio, nothing including solid rod is inherently immune regardless of the application.
https://en.wikipedia.org/wiki/Euler%27s_critical_load
"The critical load puts the column in a state of unstable equilibrium." I once accidentally loaded log hoisting shear legs made from 2x4's to precisely the critical load, where the leg would remain at whatever bowed deflection I pushed it to.
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Hi Jim.
Thanks for engaging in this line of thought.
OK - I try to avoid too many words - not as find that easy :-)
I meant "local buckling" when I only said "buckling". I know of the Euler Critical Buckling Force calculation. General bowing-out which is a distributed buckling phenomenon. Recently used it to propose the design of a sheerleg - same as the application where you offer the observation. I'd get in difficulties if I made experimental assemblies where I work - bit unimaginitive - general problem I find here of very limited outlook and not seeing success as only coming from venturing and building up experience bit-by-bit, reaching ever further into unique, valuable, remunerative (!!!) knowledge and ability.
I wondered what being on the point of the Euler critical buckling load looks like. So you do get some visible warning?
Regards, Rich Smith
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The 2" x 4" x 12' shear leg that buckled was somewhat warped so it had a cantilevered load instead of being a pure pinned-end column. It bowed slightly as the ~280 Lb log left the ground. When I saw that I decided to experiment without lifting the log further, and found it was at the point of neutral stability -- the 2x4 would hold whatever bow I pushed it to, as the equation suggests.
I switched to metal pipe whose strength I could calculate and test for the shear legs, made ball ends and socketed baseplates for them and bought a 1000Kg load scale. (Amazon.com product link shortened)
As for a warning, I suppose you could lift the load slightly off the ground and push the column sideways to see how easily it flexes, but only for thin columns, light loads and no safety margin. The column's compression strain is still within the linear region when it starts to buckle elastically. The bolts I used at the top have a bearing strength on the column walls lower than the calculated buckling load so they show overloads on inspection afterwards. I've tried a welded ring as a mechanical fuse that's visible fom a safe distance.
My degree is in chemistry, I learned electrical and mechanical engineering mostly on my own and don't trust my calculations without testing them for my home projects, solar power and moving oak logs for my home made sawmill. At work I wanted to recognize when to call in an expert from another field.
That's all. The temperature has risen to freezing and I have roof beams to replace before snow falls.
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Sorry, I had hoped your countrymen would be more helpful. 48.3mm translates to 1.90", the OD of US 1-1/2" pipe and 2" chain link fence posts, but my tabulation of commonly available (= cheap offcuts) pipe and tubing has nothing close to that ID.
Perhaps you could bore out 1-1/2" pipe tees to support your scaffold tubing fixtures. Pipe is made by a process that doesn't leave it very accurately round, especially along the weld seam, compared to DOM tubing. I chuck drawn brass pipe or a machined hydraulic fitting in the lathe so the threads run true, then screw on the rough cast fitting to turn its OD round and concentric enough to re-chuck the fitting directly to bore it.
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Hi Jim
Thanks for words of wisdom.
I noticed there is API NPS 2 schedule 80. I hadn't realised "NPS 2 schedule 80" is an API spec. That is known around the world, due to the respect for the API (American Petroleum Institute). So some chance here...
Taking tabulated specs and doing a bit of maths, that gives 49.3mm (1.939") bore, for intention to fit over 48.3mm OD (1.901"). Also now find the 1.939" bore tabulated. Which seems reasonably realistic for a fit, given experienced comments about tolerance on manufactured size and shape. Every application would have the tube split and with two plates with aligning bolt holes along the split to permit grip on the "scaffold tube". In these shorter lengths for fixtures, a die-grinder could be used to remove flash from the bore of the outer pipe, given it would be seam-welded.
Is that a common tube size as you know of? Have I got it right? This "schedule" business is about having tubes which will slide over each other, for miscellaneous practically useful reasons ?
"Streetwise" advice and comment sought!
Regards, Rich Smith
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writes:

You could also look at pipe hangers and the fittings for joining pipe hand rails. The wide repair clamp might be best if you want to line it with a friction material like hi temp gasket sheet so it could be moved with some adjustable effort, without removing gloves to loosen and retighten the bolts.
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