Aluminium tubing for telescopic support

[EddyCurrent]

Any use ?

Speaker Stand Heavy Duty Steel 063C Adjustable 35mm DJ PA 45KG - PAIR - EC | eBay

[irving2008]

Like your 'out of the box' thinking! The legs are of no use but the pole might be, depends on wall thickness. Supporting 45kg vertically is different to doing so at an angle.

[EddyCurrent]

Probably not strong enough and also too expensive

Lighting Booms & Boom Stands - Lighting | Manfrotto

[Jonathan]

Machine a bushing on the lathe and push it in the end of a tube to get the right size?

[Greeny]

Cant find anything of those sizes

All I can suggest is
2.125 + 2.250 + tube of epoxy
2.375 + 2.500 + tube of epoxy

Massive contact area, so would be a very strong bond

Ummm... But they do need to slide... And epoxy won't stop them bending under load!

Sorry not being clear ( or more likely I'm not understanding the problem)
I meant glue two tubes 2.125 + 2.250 together to form a composite thicker stronger tube
and glue two tubes 2.375 + 2.500 together to form a composite thicker stronger tube.
these two thicker stronger tubes will now slide over each other.

Cheers greeny

[irving2008]

Machine a bushing on the lathe and push it in the end of a tube to get the right size?

Could do, but all the load would be concentrated at that point and would lose some of the benefit of the combined bending resistance of the two parts together.

Sorry not being clear ( or more likely I'm not understanding the problem)
I meant glue two tubes 2.125 + 2.250 together to form a composite thicker stronger tube
and glue two tubes 2.375 + 2.500 together to form a composite thicker stronger tube.
these two thicker stronger tubes will now slide over each other.

Cheers greeny

Ah, I get you. Could simplify construction...

In the meantime, using Phill's suggestion of 25.5mm steel tubing/19mm rod I have come up with this:



Uses two tubes with cross plates welded just below top (leaving room for locking collars, not shown) and at bottom. The T-shaped foot is made of 2 bits of 3mm wall 100 x 50 bolted together with 3mm angle and flat plate joining pieces (not shown) and the tubes are bolted into the foot from the side (2 x M8 bolts each side, not shown) and the bottom cross plate bolted into the top of the foot (4 x M8 bolts, not shown).

At the top, 2 x 19mm rods are welded to a cross plate which bolts into the underside of the upper units 10mm walls using 4 x M5 bolts and also sideways through the rods into the walls of the unit using M8 bolts.

Maybe able to shorten foot once I've checked C of G of whole assembly...

[Clive S]

The link does not work for me. ..Clive

[irving2008]

The link does not work for me. ..Clive

try it again.... file was uploaded ok but something went wrong and the forum software seems to have deleted it so had to reupload :(

[FatFreddie]

Aluminium Warehouse do 2" and 2.5" 1/4" wall round tubing but only in fairly long lengths - not sure what clearances / roundness you'd get but skimming the inner should be easy enough..

Many recumbent cycles use this sort of arrangement for attaching the bottom bracket - I have a vague memory that some sizes of standard tube work well but can't find any references. ICE might be able to help you out Recumbent Trikes - ICE - Home - most of their manufacturing is done abroad now but they might have some bits for making prototypes.

I made a carbon outer tube for a recumbent by wrapping it round the aluminium inner tube and then wrapping that in insulating tape (to expel excess resin) - works well but not too great a finish. Cure it warm and put it in the freezer to separate (there might have been a layer of cling film in between as well - it was a while ago) - glass fibre would work ok and be cheaper.

I'd be tempted to use collars on slightly thicker tube unless you are being very weight concious.

Matals4u has aluminium tube in shorter lengths - Buy 3"od x 1/4" wall Aluminium Tube from Metals4u 0844 800 0069.

[irving2008]

@FF: Yes, I'd already looked at AW but as you say, long lengths :( I only need 600mm or so of each size. Been looking in eBay for offcuts but nothing suitable seen so far. Also there's no info on size tolerance so hard to tell if one fits inside the other or how well. Yes it would be possible to skim the outside of the inner tube, tho not many have a lathe that can do 600mm between centres on a 50mm tube. Not sure how you'd skim the inside on that length as you implied.

The steel tube/rod approach as drawn has the advantage of a simple welded/bolted construction. Large dia aluminum tube will need a 'plug' of some sort thus adding to the cost. Also there are plenty of examples of 20mm steel rod and 25mm x 2.5mm steel tube on eBay.

Now I've done the c of g calcs the foot can be reduced to 500mm long and 500mm wide (from 700 x 650 as drawn).