User Guide

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with any frame material, including titanium.
Butted aluminum or steel tubes are made
on a drawing bench. In this manufacturing
process, extreme force is applied to a tube
to force it through a die while a mandrel
inside the tube controls the wall thickness.
Precise control of wall thickness is provided,
while the mechanical working of the material
adds tensile strength. The strength increase
occurs because the mechanical working
alters the crystalline structure of the metal.
Its a win/win situation with lighter, stronger
tubing as the result. Similar techniques are
used to create constant wall, tapered tubes.
Examples include better grades of chain
stays, seat stays, and fork blades.
Titanium alloys exhibit very high tough-
ness and hardness, physical properties that
make titanium alloys difficult to butt or
manipulate. Like aluminum or steel, cold
working titanium orients its crystalline
structure for a stronger tube that’s more
fatigue resistant. Also like aluminum or steel,
this manipulation is expensive. Due to the
exceptional hardness of titanium, the differ-
ence in cost is huge.
To reduce the cost of butting titanium,
some manufacturers butt the tubes using a
process called chemical milling. In chemical
milling, the titanium is etched or removed
with acids. Interior chemical milling of a tube
must be carefully monitored for wall thick-
ness, requiring the extra expense of work-
ing small batches. Exterior chemical milling
is easier to monitor but decreases the outer
diameter along with the wall thickness. This
reduces the stiffness and strength of the
tube. Since the metal is not worked, chemical
milling does not provide the benefit of alter-
ing the crystalline structure of the titanium.
Another lower-cost method for butting tita-
nium is to use sheet titanium that has
been chemically milled, then rolled from the
sheet, and finally welded into tubes. This
method leaves a seam in the tube. With alu-
minum or steel, seams can be ‘normalized’ by
further drawing and cold working the tube.
Normalization is the process which restruc-
tures the molecules of the metal to reestab-
lish their original mechanical properties after
being weakened by heat. Due to the hardness
of titanium, cold working a welded seam isn’t
practical. To compensate for this weakness, a
seamed tube has to have extra material mak-
ing it heavier than a seamless tube.
A third cost-saving method for butting
titanium is outer butting, where the tube is
machined on the outside. As with exterior
chemical milling, this method makes a tube
with constant inner diameter but varied
outer diameter, reduced in the middle. The
reduced outer diameter means lower stiff-
ness and strength.
LeMond butted titanium tubing (Victoire
and Tete de Course)-
Recent advances allow 3/2.5 titanium to be
butted in the traditional way of steel tubing,
on a drawing bench. Its expensive, but pro-
vides optimal tubing shapes and outer diam-
eters, exacting precision, and works the
crystalline structure of the tube to increase
the tensile strength. The upper-end LeMond
titanium models take full advantage of
this new technology throughout the frame.
Although you can’t see it, the main triangle
is double butted.
The same processes used to butt a con-
stant outer diameter tube in the main tri-
angle is used to create the constant wall,
tapered stays (Fig T2).
Most titanium bikes use constant diam-
eter, constant thickness stays. This is
the cheapest way of making stays.
Compromises must be made between the
stiffness needed at the bottom bracket and
seat tube (defined by the outer diameter at
those joints) and comfort (defined by the
outer diameter at the dropouts).
A simple swage of a constant-wall cylinder
results in tapered stays, but with thicker
material at the dropouts. This would prob-
ably ride better, but the additional material
Fig. T2