metal strength in section

[jape]

Getting around to fabricating a rack for the Kinlon. I have a few odds 'n sods of metal around to play with, just wondering if square or round section is strongest, given all other things like material and wall thickness are the same. Square would probably be easier to fabricate from for me with basic tools but round seems (intuitively) that it might be stronger?

[*greg*]

On a geometric consideration, no other shape disipates forces and is stronger than a circle. That is why almost everything is made out of circular tube instead of square. The bending rigidity of a tube is radius to the 4th power so even a thinner gauge metal can be extremely strong.

[jape]

Thanks Greg. I haven't welded for many years and round tube is bit daunting but I can only have a go I suppose. Got plenty of scrap to try with!

[*greg*]

no worries pal

[ChinaV]

Don't know shit about welding, but hope it's one of those things I will get to learn someday.

I like to see gussets at stress points... like this.



Don't like seeing stuff flattened, as it seems this kind of stuff breaks quite often.



Cheers!
ChinaV

[jape]

Hi ChinaV. Not sure what a gusset is, but I shall take it that you indicate a reinforcing piece welded to any flattened section to relieve the stress/weakness. Do they break in your experience at the flattening point or at the drill point for the bolt? The welder seems to trip the main fuse to the house every time I start it. Damn, it is 'brand new in box' but I never opened it when I got it, so out of warranty. I may end up making this rack from bamboo!

Any way, the omens are against making this 1000 km trip to a warmer climate - I got the trailer out as it will be a car/m'bike mixed journey and it had a puncture. Fixed that, hitched it up, drove twenty meters, the car got a puncture then while I changed that the second tree for the year fell across the driveway in the wind ... I might heed the warnings, stay home and set out in a few days instead methinks. So I head to the shed, get out the welder to make a rack and 'bang', no power! I am going to stay on the couch for a week and leave the 'bike alone. The Kinlon demon wants to stay in the warm and dry perhaps?