Document 118373

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some practical knowledge over the years in aluminum framethe mountain biking experience I had there inspired me to building. Heat-treating6061 after welding requiresa hightemperaturequenchingand age-hardeningprocessthat must be
pursue my future career.Little did I know how this ride would
tightly controlled for optimal results. During quenching, the
lead me into the world of aluminum.
That day,a local trail guide loaned me his GT Zaskar-Shortly material'salloying elementsare trapped in solution, which
into the ride, I realized the bike rode far better than my own results in a soft metal. During the impurity phase of the aging
clunker with its mismatched components. lt was more process,the alloying elements form fine particles that impede
responsive,lighter and extremely rigid, making climbing abreeze. the movement of dislocations (defectsin the metal'slattice
As an engineering student at Santa Clara University, I found structure) and ultimately harden the material. Aging will occur
my young mind racing. What made this ride so well? How did naturally over time or the processcan be acceleratedat elevated
this frame's geometry compare to my cuffent bike? Did the temperatures(artificial aging).
Heat-treating 7005 after welding is straightforward and
aluminum frame offer better power transfer than steel? Could I
a low-temperature,age-hardeningprocess.The 7005
involves
bike?
design a better
have alreadybeen quenched and aged at the
tubes
butted
mechanical
my
senior
that
I
decided
beers,
After post-ride
to frame construction and welding.
prior
factory
I
design'
frame
mountain
bike
involve
must
engineering project
cracking is a known failure mode with
corrosion
Stress
credit.
for
graduation
my
frame
own
set a lofty goal to build
alloys containing high amounts of
aluminum
7000-series
of
Paul
Sadoff
skills
of
fabrication
and
the
With two classmates
is that this failure mode
layman's
understanding
My
copper.
we
framebuilder,
California
successful
Rock Lobster Cycles, a
propagation is likely to
crack
where
areas
high-stress
at
occurs
rear
inches
of
five
frame
with
built an all-steel, full-suspension
travel into crack
as
water,
such
elements,
Corrosive
occur.
three
me
to
develop
led
this
project
wheel travel. The successof
which can lead to
growth,
crack
accelerate
sites
and
initiation
my
small,
in
I996,
and
frame
design,
more generationsof this
frame
aluminum
a
7005
not
seen
I
have
practice,
In
failure.
was
born.
unofficial framebuilderbusiness
7005
because
possibly
cracking,
corrosion
stress
from
failure
frames,
custom
to
build
Sadoff
For five years,I worked with
framebuildproven
and
levels
of
copper,
low
has
tubing
bicycle
Rock
the
under
branded
primarily aggressivetrail hardtails,
ing and designpracticesaim to minimize stressat critical joints.
Lobstername.We worked with steel,the material of choice for
Aluminum frame failures due to fatigue are well
random
chance
until
custom framebuilders at the time,
although I have not directly experiencedthis
documented,
Outland
had
purchased
intervened.SantaCruz Bicycles
This meansthat at some point, after some amount
mode.
failure
the
through
and
wonder,
Bicycles,a small U.S.-basedone-hit
literally
deal,Sadoffindirectly inherited
hundreds of Outland'sEaston 7005
aluminum tubes from SantaCruz Bicycles.
It was a huge windfall of materials.
Aluminum as a bicycle frame material had
intrigued me ever since that fateful Oregon
ride on the Zaskar.I knew it was time to
branch out into aluminum framebuilding.
By 200f , I had officially launchedAhrens
Bicycleswith an immediate focus on
developing handmade aluminum
mountain bikes.
To understand aluminum framebuilding more fully, I researchedall viable
options for TlG-welded frame construction.
Two options emerged:alloy 6061 as the
first option, which gains its strength from
silicon and magnesium;and alloy 7005 as
the next option, which gains its strength
from zinc. Within the 7005 family,
ultra-lightweight scandium derlvatives
have also been developed.
With respect to handmade frame
m a c h i n el o
dwer
R e a dfyo rw e l d i n ga,nA h r e n rse a rt r i a n g lsei t si n a nA n v ifli x t u r eT.h ec u s t o m
construction, there are practical pros and
a
n
d
s
u
b
t l teo r p
r
o
v
i
d
e
s
c
l
e
a
r
a
n
c
e
p
i
c
t
u
r
e
,
a
m
p
l
e
t
i
r
e
o
f
t
h
e
y
o
k
e
,
i
g
h
s
t
i
d
e
l
o
w
e
r
i
n
t
h
e
v
i
s
i
b
l
e
or
7005
6061
cons when dealingwith either
g r e aat c c e l e r a t i o n .
j
o
i
n
e
d
f
o
r
c
h
a
i
n
s
t
a
y
s
r
e
c
t
a
n
g
u
l
a
r
s
t
o
u
t
t
o
a
n
d
i
s
s
i
o
n
a
J
l
l
e
x
in
is
readily
available
aluminum. Alloy 6061
a wide variety of sizes and shapesfor
of cyclic loads, the material will fail when it reachesits
machining frame components. Conversely,alloy 7005 is only
endurance limit. In the bicycle world, this usually translatesinto
malleable
and
are
Both
alloys
sizes.
offered in limited useful
years of riding on the same frame without failure. Some of
many
methods.
easily machined by conventional
aluminum frames are still being ridden, and one
my
earliest
gained
I've
but
material
scientist,
or
I'm not a metallurgist
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advantageof the tubing supply that
Sadoff had acquired from the
Outland sale.
Framecomponentssuch as
dropouts, cablestops and bottom bracket
shells were readily available from a local
distributor, and I assumedthat moving to
this new alloy would be painless.That
was a bad assumption. The off-the-shelf
frame componentswere poorly designed
and quality was moderateat best.
Theseparts had to be reworked by hand
to achievea decentaesthetic.I was
clearly disappointed with the available
frame componentsand new versions
of theseparts were required for my
handmade frames.
I encountered a new challenge when
I found that any weldable frame
componenthad to be machined from
7005 alloy using bar stock offeredonly in
a l-inch by 4-inch format. This bar stock
size is not ideal and has limited design
creativitysince eachframe component
must fit within this pre-definedoutline.
What if I wanted to designa
chainstayyoke that was I.5-inch thick
and 4.25-inch wide? Theseideaswere
not possiblebecausethe largest7005
aluminum blank size was too small. And
my dropout designswere less than
L-inch thick, meaning extra material
was wastedduring CNC machining.
Overall the transition to 7005 had a
steeplearning curve.
Tuning stiffness characteristicsfor
each rider is one of my primary
motivations when building handmade
aluminum frames. Through extensive
R&D, I've discoveredthat aluminum
frames can be highly tuned in a fashion
similar to steel frames. In the front
triangle, different styles of tubing can be
combined to provide the desired stiffness
level, from race-specificapplicationsto
everyday trail riding.
For example,changingthe down
tube'soutside diameter and butting
profile has an immediate effect on ride
quality. In addition, tube-end ovalization
can be further tweaked by hand to
achieve different stiffness levels.
The most advancedtuning of my
aluminum frames happens in the rear
triangle by combining the custommachined yokes I've developedwith
select tubing shapes.Riders can
perceive the aluminum frame'storsional
compliance during trail riding.
This means that the rear triangle "gives"
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