R
On Jul 26, 11:26 pm, [email protected]
(D.M. Procida) wrote:
> Ian Smith <[email protected]> wrote:
> > > I believe that the frame tubes' varied wall thicknesses are created by
> > > hydraulic expansion. This is where high pressure is applied inside the
> > > pipe to expand the inner dimension (and increase length slightly) but
> > > maintains the outer dimension due to the tube being held in tooling
> > > that prevents change. This only works on round extrusions, however,
> > > with final forms, like a diamond or elliptical section requiring
> > > rework after the tube has been hydraulically altered as above.
>
> > As written, that sounds like bollocks to me.
>
> > Not least because it requires hydraulic fluid inserted into a circular
> > tube to exert greater pressure on one part of the wall than on an
> > adjacent section. Fluid doesn't do that.
>
> > It could possibly work to vary wall thickness along a tube, but the
> > situation under discussion is varying thickness around a tube.
>
> "but maintains the outer dimension due to the tube being held in tooling
> that prevents change."
>
> Daniele
Well, it's not bollocks! How can a traditional lathe or machining
centre change the wall section of something like a bike frame tubular
section? The cutting tools wouldn't be able to reach too far into the
opening as, as far as I know, triple butted frames are thinner at the
middle than the stressed ends. By blocking the relevant sections of
the tubular frame and applying pressure, wall thicknesses can be
changed at any point along the tube.
The same process is used to expand tubes along a long length or to fit
thin walled sections into a particular shape otherwise known as
hydroforming - same process, different application (for aly based
tubes anyway). I think GT Bikes have a document on this, I seem to
remember.
You can also "draw" the material through a die to give different wall
thicknesses.
Russtler
(D.M. Procida) wrote:
> Ian Smith <[email protected]> wrote:
> > > I believe that the frame tubes' varied wall thicknesses are created by
> > > hydraulic expansion. This is where high pressure is applied inside the
> > > pipe to expand the inner dimension (and increase length slightly) but
> > > maintains the outer dimension due to the tube being held in tooling
> > > that prevents change. This only works on round extrusions, however,
> > > with final forms, like a diamond or elliptical section requiring
> > > rework after the tube has been hydraulically altered as above.
>
> > As written, that sounds like bollocks to me.
>
> > Not least because it requires hydraulic fluid inserted into a circular
> > tube to exert greater pressure on one part of the wall than on an
> > adjacent section. Fluid doesn't do that.
>
> > It could possibly work to vary wall thickness along a tube, but the
> > situation under discussion is varying thickness around a tube.
>
> "but maintains the outer dimension due to the tube being held in tooling
> that prevents change."
>
> Daniele
Well, it's not bollocks! How can a traditional lathe or machining
centre change the wall section of something like a bike frame tubular
section? The cutting tools wouldn't be able to reach too far into the
opening as, as far as I know, triple butted frames are thinner at the
middle than the stressed ends. By blocking the relevant sections of
the tubular frame and applying pressure, wall thicknesses can be
changed at any point along the tube.
The same process is used to expand tubes along a long length or to fit
thin walled sections into a particular shape otherwise known as
hydroforming - same process, different application (for aly based
tubes anyway). I think GT Bikes have a document on this, I seem to
remember.
You can also "draw" the material through a die to give different wall
thicknesses.
Russtler
