# Square section steel tube



## Chris152 (24 May 2019)

Mild or stainless, can you get it with square corners? I've searched and it all seems to have rounded corners - is that just the way it's made? I'm looking for about 80mm square x 3 metres.
Thanks, C


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## sunnybob (24 May 2019)

The corners on steel tube are rounded because its made from flat, bent over formers, and welded down the middle.
The only way to get sharp corners is on cast extruded ali.
Or, grind all sides flat yourself.


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## Chris152 (24 May 2019)

Thanks sunnybob. What would the strength of this
https://www.aluminiumwarehouse.co.uk/4- ... quare-tube
be compared to the same section in steel? It'll span a gap about 1.7 metres - what kind of weight might the ali support before bucking/ bending - if someone sat heavily on it would it give? (It's not for people to sit/ stand on, just to look at, but you never know...)


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## sunnybob (24 May 2019)

Thats above my pay grade I'm afraid. :roll: 
Click the link again, theres an "ask a friend" box with a guaranteed reply in 1 hour during working hours.


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## Eric (24 May 2019)

As well as the standard and very rounded corner box section mild steel, you can also buy ERW box section, which comes with much tighter radius corners. 

Lots of places sell it, Metalmaniauk are fairly good if you only want a small quantity. They have 80mm ERW. 80mm ERW box


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## Lazurus (24 May 2019)

Could you use the Ali and reinforce with a steel rod or square inside?


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## t8hants (24 May 2019)

Not if its going to get wet, you will make a battery and the ali (IIRC) will slowly corrode away.


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## novocaine (24 May 2019)

http://metalgeek.com/static/deflection.php

Wish this stuff existed when i did my degree and had to do the calculations for myself. 

Pick a fat bloke. Assume hes sat on a pin for worst case.


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## Trevanion (24 May 2019)

What is it actually for? Does it really need to have _sharp_ square corners? I personally would much rather something have a bit of a radius at circa £20 rather than sharp edges at £120, especially if it's going to be weaker due to a different material or thinner wall to accommodate tighter radii. 




sunnybob":15iqphh3 said:


> The corners on steel tube are rounded because its made from flat, bent over formers, and welded down the middle.


Never knew that, learn something new everyday!


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## Chris152 (25 May 2019)

Thanks all. It's for a sculpture I want to make and will be mounted horizontally onto wooden uprights, supported toward (but not at) the ends. As I say, it'll carry no weight apart from its own but you never know who might try sitting on it. That said, the ERW that Eric linked to looks square enough at the corners and is relatively cheap - if someone did bend it, it's not so expensive to replace.

In my efforts to find out what ERW is, I read this:
'What is the Difference Between Seamless and ERW Stainless Steel Pipes?' - http://pearlitesteel.com/erw-stainless- ... rom-india/
so, not as strong as seamless ('It is mainly used for low/ medium pressure applications such as transportation of water / oil.') but I think it might do the job. Stainless steel would look nicer, though!

edit - novocaine - I followed the link which looks like it answers my question about strength/ movement, didn't really understand all the details but can see switching between mild steel and ali results in far greater deflection for ali.


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## Inspector (25 May 2019)

Thanks novocaine. Great calculator and I bookmarked it.

Chris the aluminium would only deflect half a millimetre if a 150 kilo person sat on it and when they get off it will return to straight. A steel one would deflect a fifth of a millimetre. The only thing you have to watch out for is mixing your metals as there is the possibility/probability of corrosion. You wouldn't want to use steel uprights to hold the aluminium horizontal part without using proper sealants, cadmium plated or stainless steel bolts and having the metals treated or painted the same way aircraft are built.

Pete


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