Simple engineering question?
Discussion
I'm looking for a length of aluminium tube to fulfil the following criteria:
3m length
minimal flex
minimal weight
to support up to 2kg weight
So my question is, does anyone know what diameter & wall thickness would I need to ensure the minimal flex/weight criteria with 2kg attached to the end of it?
many thanks in advance!
cheers,
Steve
3m length
minimal flex
minimal weight
to support up to 2kg weight
So my question is, does anyone know what diameter & wall thickness would I need to ensure the minimal flex/weight criteria with 2kg attached to the end of it?
many thanks in advance!
cheers,
Steve
Oldandslow said:
There are not enough detailed criteria to give you an answer. Minimal flex, minimal weight, too vague 
I'd suggest trying a bit and seeing if it meets your needs, or Bosch type profile if you can get some.
Ah OK, what else would you need? I'm basically just after the lowest weight & diameter I can find that will ensure almost no flex with the criteria stated above.....I'd suggest trying a bit and seeing if it meets your needs, or Bosch type profile if you can get some.
O.K. I might be wrong, but I've quickly calculated here (on paper, unchecked) that a 4 3/4" dia nominal aluminuim rod will flex by 10 thou in your three metre length, with your 2 kilo load.
If the numbers are right, and they don't sound too bad (but what do I know?) that's a hefty bar. My numbers wouldn't take into account the weight of the bar. I'm pretty sure that if you just picked up such a piece of material with a sling in the middle you'd be able to see the sag easily.
The thing is that 10 thou is more than not a lot. It's always going to move.
You have to have a structure or otherwise it's a pointless exercise. It proves to me what I knew already, which is why I can't be bothered to check the numbers.
By using a structure, you put the material into tension or compression, and then you are using the material in a much better way. Just off bat, I'd say you could achieve 100 thou in three metres, with thin wall ally tube about an inch in diameter. But you'd have to use a triangulated ladder type strut. An alternative would be a big old I beam. Ally is soft and bendy, using better materials would help too.
The biggest thing most people are familiar with is a house. They don't move that much, because they're usually made of brick. Brick doesn't bend at all, but it will break. That's presumably why you're using metal, because you want it to bend, not break.
If the numbers are right, and they don't sound too bad (but what do I know?) that's a hefty bar. My numbers wouldn't take into account the weight of the bar. I'm pretty sure that if you just picked up such a piece of material with a sling in the middle you'd be able to see the sag easily.
The thing is that 10 thou is more than not a lot. It's always going to move.
You have to have a structure or otherwise it's a pointless exercise. It proves to me what I knew already, which is why I can't be bothered to check the numbers.
By using a structure, you put the material into tension or compression, and then you are using the material in a much better way. Just off bat, I'd say you could achieve 100 thou in three metres, with thin wall ally tube about an inch in diameter. But you'd have to use a triangulated ladder type strut. An alternative would be a big old I beam. Ally is soft and bendy, using better materials would help too.
The biggest thing most people are familiar with is a house. They don't move that much, because they're usually made of brick. Brick doesn't bend at all, but it will break. That's presumably why you're using metal, because you want it to bend, not break.
Edited by dilbert on Monday 12th April 02:43
Pigeon said:
No, a 3m length of that with 2kg on the end will be dead bendy.
But we don't know that the 2kg is going on the end, he just says "to support up to 2kg" he doesn't say it's going at the end so for all we know it may be going in the middle. The point is that we need more info. ETA - Whoops my mistake, he does say "at the end" I missed that bit so ignore my post then
Edited by 109 Bob on Monday 12th April 03:12
What you want is 1.5" Aluminium Conduit. Works a charm and fits Manfrotto clamps.
Outside dia is 1.9"
http://www.globaltecheng.com/alupipe.htm
Outside dia is 1.9"
http://www.globaltecheng.com/alupipe.htm
109 Bob said:
Pigeon said:
No, a 3m length of that with 2kg on the end will be dead bendy.
But we don't know that the 2kg is going on the end, he just says "to support up to 2kg" he doesn't say it's going at the end so for all we know it may be going in the middle. The point is that we need more info. ETA - Whoops my mistake, he does say "at the end" I missed that bit so ignore my post then
Nor does he define "minimal weight" or "minimal flex". To answer it literally in terms of the thread title - as an engineering question - your point that we need more info still holds. It's not possible to give an engineering answer.
But my point is that the question as posed, in those vague terms, isn't actually an engineering question. It's a bodging question... so it is valid to provide a bodging answer
Assuming horizontal orientation in an attempt to give some margin, if I was doing a bodge which fitted that description, I would probably consider the pipe idea but immediately discard it as 3m of 1.5" ABS waste (sink pipe) will sag under its own weight, and indeed probably won't be straight in the first place, plastic pipe never is.
But dinghy masts are pretty light and stiff, so I would certainly haul a chunk of that out of the junk pile and play with it.
That would very likely be a workable bodge for a statically loaded structure. A version to handle dynamic loading - eg. if it was to be fixed to a moving vehicle - would need to be guyed and/or braced, with eg. bicycle brake cable and/or lengths of 2x1, or reconceived altogether as a better optimised structure.
The load will be on the end, supported horizontally. For example:
One end would be clamped in two places (e.g. suction cups on a car bonnet), 0.5m apart - the load (a camera) would be at the other end so it would only apply bending force over 2.5m
Ideally it would have no flex at all, but of course this is not realistic without going for very heavy and/or expensive solutions! So a little flex once the camera is attached is OK, the main thing is that it has minimal flex whilst moving (which would only be done at very low speed). It sounds like a good solution would be to setup some kind of cable suspension over the top of the tube to help keep it in tension.
One end would be clamped in two places (e.g. suction cups on a car bonnet), 0.5m apart - the load (a camera) would be at the other end so it would only apply bending force over 2.5m
Ideally it would have no flex at all, but of course this is not realistic without going for very heavy and/or expensive solutions! So a little flex once the camera is attached is OK, the main thing is that it has minimal flex whilst moving (which would only be done at very low speed). It sounds like a good solution would be to setup some kind of cable suspension over the top of the tube to help keep it in tension.
Bob_Defly said:
What you want is 1.5" Aluminium Conduit. Works a charm and fits Manfrotto clamps.
Outside dia is 1.9"
http://www.globaltecheng.com/alupipe.htm
Excellent, but for the lack of a Euro-rep Outside dia is 1.9"
http://www.globaltecheng.com/alupipe.htm
Check out these guys :
http://www.mbsitem.co.uk/ for their range of ITEM aluminium profiles,
it is like "Fischer Technik" for grown-ups, you can build anything with it,
and attach bolts (camera holder) to the profiles at any point.
http://www.mbsitem.co.uk/ for their range of ITEM aluminium profiles,
it is like "Fischer Technik" for grown-ups, you can build anything with it,
and attach bolts (camera holder) to the profiles at any point.
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