butting tubes

[p3ntuprage]

thought someone here might know about this type of thing:

how exactly is it done?

is it a mechanical or a chemical etching type process?

in either case, wouldn't it be easier to do it on the outside of the tube rather than the inside?

fsnl
sparky

[LWaB]

Usually a mandrel, as the tube is being cold-drawn.

[Peterpan1]

I don't know how they do it. Cold drawing would be a stretch.

It is possible to do it on the outside, rather simply if you have a lathe, there are three problems with doing it that way:

1) Stiffness and strength is related to the cube and square, repspectively, of tube diameter. So reducing the outside diameter of the tube reduces it's stiffness significantly, and it's strength. This is not a problem in all cases, but where the yield is related to the flexing of the tube, or to the tube remaining in column it would be a significant factor even in the small degree that butting involves.

2) Looks as though they taper in the middle even when parallel, the tube that is also waisted will look even less straight, which is one reason for swell in collumns in building.

3) Easier to have any tool marks or shoulders that might be stress risers on the inside where they have minimal load bearing in comparison to the outside.

Seat tubes are externally butted or they would not have a constant support for the post. And since most of the loading is parallel to the surface, the stress riser and tensile issues are minimal.

I have heard of some big name companies that adapt 4130 aircraft tubbing to particular uses, like oversize elements. In order to reduce weight they externally shave the tubes. They can deal with the aesthetic issues with paint.

[shandcycles]

As LWaB says.

see here: http://www.reynoldscycles.co.uk/buttedtubing.html

[p3ntuprage]

very interesting. thanks.

[who'd have thought so much work would go into saving a few hundred grams on a frame?]

fsnl
sparky

[Cyclepath]

Butting also improves the ride quality. I believe that's the main reason for it, more than weight saving.

[rmfnla]

Cold drawing would be a stretch.


Funny; was that intentional?