Stiffening a length of copper pipe

On 03/11/2018 03:56, snipped-for-privacy@gmail.com wrote:

Seems to me that what you want is something that is springy in torsion, but stiff to bending forces.
TNP, do you have any references on this?
Andy
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That’s not correct. It’s a lot lighter than a metal one.
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On 30/10/2018 10:33, Chris Hogg wrote:

I think a sand/cement "grout" might be OK but messy / fiddly. I don't think vibration would compact sand sufficiently to prevent a small sag. I'd be inclined to look at the chromed steel tubing which is sold for wardrobe rails which I'm sure is going to be significantly stiffer. IIRC usual diameter is about 20 mm. Plenty in Screwfix, both round and oval.
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After serious thinking newshound wrote :

..and near impossible to get to fill the pipe.
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Remember Cement is only strong in compression.
Brian
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On Tue, 30 Oct 2018 20:06:57 -0000, "Brian Gaff"

Yebbut, that's unconstrained cement. In a tube, where it's constrained, it will behave differently, although IANA civil engineer so can't say how in detail. But if you try and bend an open copper pipe, at some stage it will kink and flatten. Concrete inside it will stop that. Anyway, I was looking for stiffness not strength as such.
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On 30/10/2018 20:31, Chris Hogg wrote:

Exactly. It wont help a lot. Its quite elastic in compression* and rips apart in tension
*you would be surprised how much bounce there is in a block-and-beam floor.
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On 30/10/2018 10:33, Chris Hogg wrote:

20mm steel conduit - ideally the black enamel - if you can find someone local with stock?
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19mm RHS is better, thicker walls and rather easier to find now.
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Yes its seemed but rather springy unlike copper which will just bow permanently. Also what about some bamboo? Brian
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Its not as stiff to sideways bending at that diameter as steel. stainless is stiffer again, but not cheap at all.

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On 30/10/2018 10:33, Chris Hogg wrote:

The stiffness of the pipe depends on: 1. The diameter - the bigger the better. 2. The thickness of the walls of the pipe - the thicker the better. 3. The material. Steel is much stronger than copper.
Perhaps you could use some old gas barrel?
Otherwise, could you support it at various points along the length, so it doesn't need to be as strong?
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On 30/10/2018 11:03, GB wrote:

Wrong. Steel is much stiffer than copper.
Strength doesn’t come into it
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<snip> >*it's a length I have spare, but I could get some 22mm pipe if it

I think the key here is having a good vertical section. Flat strip would be good but would flop sideways so you also need some horizontal section to manage that.
So, a light rectangular box section steel or if you can get some 22mm copper in there, what about two lengths of 15mm solder tacked (taped for testing) together and used 'over and under' / Fo8?
Cheers, T i m
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On 30/10/2018 10:33, Chris Hogg wrote:

Yup I see what you mean, that has quite an impact!
Steel conduit would certainly be an option. You may also be able to get a length of oval or round wardrobe hanging rail. They may be stiff enough.
However one option would be to arrange the wall mounting so that you can put the pipe under tension. It ought to be possible to fashion a couple of attractive wood mounts with holes for the pipe to pass through (and that you can cross drill to allow a screw to intersect with the pipe to retain it), then a moveable part of one or both mounts, screwed laterally to a fixed bit so you can tighten the screw and pull it taught.
Another option would be self adhesive velcro strip. Fix a wood batten to the wall with "hook" bit of the strip fixed to it, and then place the fluffy bit on the back of the cloth. You can then stick it in place. (a few stitches on the cloth may be wise)
(you could even do a full frame like that, so that its supported at the sides and bottom also, and which could then be "hung" like a picture)
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Chris Hogg wrote:

Steel conduit is about 20mm. I use it for wardrobe rail and plenty strong enough. Black or BZP finish available
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On 30/10/18 12:18, Bob Minchin wrote:

I'd advise against (bare) copper. It will react with humidity in the air perhaps the chemicals in the dyes in the fabric- possibly damaging your wife's hardwork.
(I speak from experience, although not with copper pipe. Around the time we met (some 40+ years ago) my wife did a very intricate embroider picture. It hung for years in our bedroom. It had been framed- we bought the frame and I think she did it framed it herself. Over the years, the chemicals from the backing board stained the background. We've later learned there are techniques to prevent this- several but that is not relevant here.)
You could cover the pipe in plastic sleeve, the kind used to cover wires, it is cheap and available in various sizes. Heat shrink would be good but expensive for that much.
I'd be equally wary of galvanized or bare steel.
To stop/reduce bending, a bit of dole, covered in epoxy, and forced in would probably do the job.
However, I'd use either a chrome tube for a wardrobe rail- if it will fit. These a rigid.
OR a length of 15mm stainless pipe. That will also be rigid.
Neither are likely to react with moisture and/or chemicals in the dye.
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Something like Dexion Speed Frame instead? 1in square steel tube and very strong - comes painted in black too for about 10 quid for 3 metres. Other colours too.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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I'd use 19mm RHS, square steel tube or 12mm if 18 mm wont fit.

Not enough to matter in that situation.

Yeah, I doubt it would be.

I doubt it.

You'd be better with the non annealed stuff if you use copper. Personally I'd use RHS, its quite a bit stiffer. Solid stainless steel rod even stiffer but not cheap.
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On 30/10/18 10:33, Chris Hogg wrote:

Slide another pipe inside of it - B&Q have tube in ali and steel in a variety of sizes - it need not be a perfect fit.
Or dry sand and some repair/casting resin soaked into the sand (Halfords may still sell this for use with fiberglass)
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