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DannyC
10-12-2013, 01:39 PM
Hi Folks,

I wondered if anyone had tried using elliptical tubing in any builds, and if so what their experiences were?

As I understand it the "rounder" a section gets the easier it is to bend. Clearly the use of square or oblong tube sections provides a level of strength & rigidity but perhaps with a weight penalty.

I noticed that one of my "donor" bikes (non- DF) had its main beam made of an elliptical tube with the flatter side(s) in the vertical plane (to give strength, presumably).

So I wondered if anyone had tried elliptical tubing yet in any builds at all ;-)

http://www.eliptec.co.uk/product-range/ have it in a wide range including the one used in my Donor bike 66 x 33 @ 2mm which sounds promising to me.

I quite like the look of it myself but I do not know how structurally sound it is in comparison to the square profiles we are all used to.

Any ideas? I shall do a trawl to see what I can find and report back.

Regards,

Dan.

sandman
10-12-2013, 02:34 PM
Hi Folks,

I wondered if anyone had tried using elliptical tubing in any builds, and if so what their experiences were?

As I understand it the "rounder" a section gets the easier it is to bend. Clearly the use of square or oblong tube sections provides a level of strength & rigidity but perhaps with a weight penalty.

I noticed that one of my "donor" bikes (non- DF) had its main beam made of an elliptical tube with the flatter side(s) in the vertical plane (to give strength, presumably).

So I wondered if anyone had tried elliptical tubing yet in any builds at all ;-)

http://www.eliptec.co.uk/product-range/ have it in a wide range including the one used in my Donor bike 66 x 33 @ 2mm which sounds promising to me.

I quite like the look of it myself but I do not know how structurally sound it is in comparison to the square profiles we are all used to.

Any ideas? I shall do a trawl to see what I can find and report back.

Regards,

Dan.
Get behind me ***** (horned evil thing, I hope thats allowed. with your devilish words of elliptical tube, dont you think I have enough ideas and projects going on , but a few ideas do spring to mind
:cheesy:

John

bambuko
10-12-2013, 03:54 PM
I seem to remember not so long ago someone complaining :) that life uphill was tough...
66x33x2mm - what are you building? ships?
Just because it was used on the donor bike doesn't mean it was any good :-)
1.5mm is perfectly strong enough (actually too strong, but the limiting factor is the ability to weld thin wall)
Eliptical or oval is fine, but not really necessary (and added complication when it comes to joints) - doesn't offer anything that cannot be achieved with equivalent rectangular section.

Why do you want to use it? What do you hope to achieve?
Rectangular (not square) is stronger in one direction than the other (similar for eliptical/oval sections)...

DannyC
10-12-2013, 05:56 PM
Thanks (I think... LOL) John and Bambuko.

I am only bouncing an idea around, not committing to a plan.

Yup 1.5mm is probably plenty strong enough, I am interested because round-tubes are perceived not to be as strong as square or oblong and this seemed to offer possibilities.

I agree that the joints might be "problematic" (to say the least), but the elliptical tube seems (to my eyes) to be more aesthetically pleasing than square or oblong.

The actual available ranges (if you looked) are:


http://s5.postimg.org/5b4rkypgj/eliptic.jpg (http://postimg.org/image/5b4rkypgj/)

So there seems to be plenty of scope to go elliptically "hog-wild" if one wanted to.

As i say, I'm just thinking "out-loud" as it were.

Regards,

Dan.

darnthedog
10-12-2013, 07:22 PM
Sounds like your tired of being square o'daddy'o- LOL

FrankCrank
10-12-2013, 08:26 PM
...hey Dan, my guess is that 1.2mm would be quite adequate, but then you need to be able to weld the stuff of course. On my mk2 trike I will be using 50x25x1mm stainless for the main frame structure, and will attempt to double up the joints to 2mm where possible. Will cut off a short section of same tube and make a slots in it and bash into the ends of each tube to effectively double it for easy welding - if that makes sense? I'm not a weight weenie :) but am aware that I'm building a trike and not a tank..........

bambuko
10-13-2013, 05:28 AM
...round-tubes are perceived not to be as strong as square or oblong...

There is nothing to "perceive" about it :evilgrin: - it's a matter of mathematics and engineering formulas, furthermore to say that round is not as strong as square is missing few dimensions from the discussion (ie wall thickness and size of the profile) and simply wrong.
Given the right wall thickness and tube size you can make it equally strong using either square or round, although bear in mind that if the profile is asymmetrical (whether rectangular, oval or elliptical) it will be "stronger" in one axis.

go1000go
10-13-2013, 05:41 AM
Hi Danny
Can see what you mean regards aesthetics, however just turning the square through to a diamond makes the look of square tube so much better.
Also the joints then are easier to work out.
My first mtb 4 years ago had a tube that started rectangle and finised oval, hydroformed.
Sketch some ideas and post them.
Tim

DannyC
10-13-2013, 07:56 AM
There is nothing to "perceive" about it :evilgrin: - it's a matter of mathematics and engineering formulas, furthermore to say that round is not as strong as square is missing few dimensions from the discussion (ie wall thickness and size of the profile) and simply wrong.
Given the right wall thickness and tube size you can make it equally strong using either square or round, although bear in mind that if the profile is asymmetrical (whether rectangular, oval or elliptical) it will be "stronger" in one axis.


Hi Bambuko,

I agree that you have to compare "like-for-like" as far as is possible, and had hoped that common-sense would have automatically inferred that "comparable" tubes (elliptical, square or oblong) i.e. what would be the comparable strength of a 3 x 2 oblong in 1.2 or 1.5mm Vs. a 3 x 2 in elliptical in the same gauge?

Clearly you cannot have a 3 x 2 square tube or round tube, but you can have a 3 inch square or 3 inch round tube in that gauge.

i.e. Does the elliptical only possess X% of the rigidity of the oblong variant in the vertical plane, and what is its relative strength compared to a square or round tube of the same major dimension (i.e. 3 x 3 Sq or 3 inch diameter tube of the same thickness)?

I was only asking if anyone knew. I wasn't trying to start a contest or a major debate. ;-)

Regards,

Dan.

FrankCrank
10-13-2013, 08:48 AM
...nothing wrong with starting a major debate - dull world if we all thought and did the same thing:evilgrin: .

Way I see it, most loading on a bike/trike is vertical, so seems logical that rectangular section is the best option - others may differ in opinion, but can only state my instinct on this. One thing I've picked up on in recent purchase of stainless tubing, is that rectangular/square is a lot more expensive( at least double) than round tube, given like for like size/guage. A cynic might say manufacturers mostly use round section to save money, disregarding the extra strength benefits rectangular would give.

So there you have it, tossed in my grenade, now I'll do a runner and see what happens....:joker:

bambuko
10-13-2013, 09:40 AM
...I wasn't trying to start a contest or a major debate. ;-) ..

neither was I :)
Just trying to educate - ability to withstand bending stress is related to second moment of area (moment of inertia) of the beam in question.
Calculate moment of inertia for each tube and you will be able to compare them.

Not much to debate either :evilgrin:

and as for cynics...