Aluminium alloys...

How do you know what alloys the different frames are made of?

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you just go www.krisholm.com, www.koxx-one.com and or www.google.com 🙂

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Ntappin said:

I'm a butcher, and it took me like 10 minutes to get one nub off my
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2nd *)---TreFlip-'O,
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Sponge said:

I've had bad experience with biketrials cranks made of 6061... thread
strip is something that's not uncommon.

At least you got 4 good rides out of them 🙂

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thejdw

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kington99 said:

A hobnob is an oaty biscuit, the fact that they don't exist in america
just goes to show that you have no culinary heritage 🙂

Quoted message said:

Quoted message said:

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It's also important to note that some manufacturers hide the type of
alloy they use by using marketing catch-phrases like "Ultra-C" or
"Optim-AL" that make it hard to tell what alloy they are using. In
probably 100% of those cases there is no special metallurgy being done
by the bike manufacturer- they just want to brand their product as
unique and that's hard to do when numeric alloy specifications are
published and well-known.

Aside from the basic specs it's also important to consider reliability
of performance in the manufacturing process. Uncommon alloys (like
Ultra-6) have good strength characteristics but can be difficult to use
with consistent high quality. A strong frame material is no good if a
higher percentage of those frames fail due to manufacturer defects, due
to construction challenges.

Consequently, I feel that 7005 Aluminum is an ideal material for uni
frames. It's much lighter than titanium (by volume) and is stiffer
than most titanium tubing of comparable weight. It's twice as
expensive as steel but has much better strength-weight characteristics.
That is why most DH bike frames are 7005 Al.

Although our frames do get bashed around, the loads they are forced to
take are not at all comparable to a bike frame because (unlike bikes)
loads off drops on a unicycle aren't taken directly by the frame.
Consequently, opinions on this newsgroup notwithstanding, I don't feel
that material fatigue is a big issue, or at least it is something that
can certainly be taken into account with proper design.

Kris

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I should add that that's not a criticism of titanium frames- Ti is
clearly also a really good material. In any case, good design trumps
material choice for most things.

K.

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"It's also important to note that some manufacturers hide the type of
alloy they use by using marketing catch-phrases like "Ultra-C" or
"Optim-AL" that make it hard to tell what alloy they are using. In
probably 100% of those cases there is no special metallurgy being done
by the bike manufacturer- they just want to brand their product as
unique and that's hard to do when numeric alloy specifications are
published and well-known."

In an aside to this comment by Kris it may be very hard for low end
manufacturers to continue to make claims like this in North America, as
I am being lead to believe by the cycle community that much tougher
restrictions are in the works in order for bikes and their components
to meet what may soon be ISO standards.

Among many other restrictions, frame materials and welding quality may
come under the gun and substandard frames will not be allowed (too many
cheeper bike frames are breaking and causing injury even in general
riding conditions)

Competitors in different catagories i.e. trials, bmx etc type
competitions may soon have to prove that they are riding on certified
frames.

Time will tell.

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Harley

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I watched a movie recently, "the John Britten story", about a garage
craftsman who constructed an entire race motorcycle himself, and won
some super bike races in the early 90's. The frame, hubs and rim were
made of carbon graphite.
The entire bike weighed 303 lbs.

Presumably a motorcycle rim has a tougher job, and needs a bigger
safety margin then a unicycle. It's been over a decade, why isn't
anyone selling carbon uni frames ? Is it purely a cost-market size
thing ? Or is there something about carbon frames that makes them
inferior to metal ?

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They have. Roger Davies handmade the original high-end uni frames from
carbon in the 90's and still rides one. But it's expensive to produce
and cost-effective designs usually have a machined aluminum crown and
bearing housings, so the weight savings isn't necessarily all that
much.

Kris

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feel the light said:

I watched a movie recently, "the John Britten story", about a garage
craftsman who constructed an entire race motorcycle himself, and won
some super bike races in the early 90's. The frame, hubs and rim were
made of carbon graphite.
The entire bike weighed 303 lbs.

That guy was truely amazing! I was a big fan of race bikes back then
and I remember when his bike came out. Not only did he design and
finance that bike himself, he had no engineering background (he was an
architect). His bikes were compettitive w/ $300,000 factory
Superbikes.

He died of cancer at only 45 in 1995🙁 The motorcycling world truely
misses him.

feel the light said:

Presumably a motorcycle rim has a tougher job, and needs a bigger safety
margin then a unicycle. It's been over a decade, why isn't anyone
selling carbon uni frames ? Is it purely a cost-market size thing ?
Or is there something about carbon frames that makes them inferior to
metal ?

A carbon uni frame and wheel rim would be cool, but pricey. I think
the uni market would have to grow quite a bit.

I think a good full suspension uni would be better, but CF could help
keep the inevitably higher weight down.

...also more development into multiple gears.

Sorry for the threadjack.
Back on topic.

Edit: wikipedia says he was a mechanical engineer, maybee I'm
remembering that wrong.

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skilewis74

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I think Kris's choice of frame material is a good one. There is no need
to increase price for a mild, if negligible improvement in performance.

I do however believe fatigue life is an important part of frame stats,
especially in relation to welded areas. It is much harder to measure,
and usually harder to find for the more obscure alloys.

Another (less important) note is corrosion resistance. If there is a
way for water or something worse to get into a frame tube and eat out
weld joints from the inside, a strong, but corrosive alloy is a bad
choice. Yes, water is corrosive, by the way. Look up carbonic acid if
you want to know more.

Sponge said:

]
Material | Mechanical Properties | *Ultra 6 | 6061 | 7005 *
Tensile | Kg/mm | 42.0 | 31.5 |
35.0
Yield Strength | Kg/mm | 36.5 | 28.0 | 30.5

Elongation % | in 2 inches specimen | 12.0 | 12.0 | 11.0

I'm sorry, kg/mm? Kilograms are a unit of mass, and tensile strength is
provided in units of force/distance, such as pound/inch or kN/mm
(kiloNewtons/meter).

Where did you get this information? I am a little bit skeptical of any
source that doesn't bother to check its units. Which is not a criticism
of you. I don't have my machinery's handbook with me in college (it
includes this information for nearly all major alloys of aluminum,
steel, titanium, and bronze/brass), so i can't check those figures.

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whoops, kiloNewtons/MILLImeter

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carbon fibre is in some ways a fragile material. The kind of damage that
dropping the frame on to rocks would cause would soon initiate cracking
and ultimately cause failure. Roger can get away with it because he
never falls off. He always wraps his frame up when it's in transit
because just banging around in the back of the car may well be enough
to cause damage that leads to cracking. I believe a batch of 30 of the
Roger Davies mk 5 were made, last time I saw they were selling at £800
each.

As for a rim, the problem would be even worse, hard muni would put
chips in it that would lead to premature failure. Of course a
motorcycle rim takes more force when riding, but when taking a uni off
a six foot drop i'm not so sure. A carbon coker rim would be brilliant,
lower risk of damage and the weight saving would be more worthwhile on
a rim that big.

--
kington99

Dave

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gerblefranklin said:

I'm sorry, kg/mm? Kilograms are a unit of mass, and tensile strength is
provided in units of force/distance, such as pound/inch or kN/mm
(kiloNewtons/meter).

QUOTE]

Glass houses and stones!!
Ultimate Tensile Stress should be quoted in units of force/area,
usually for this type of material that would be N/mm2.
Yield? I can't be certain for these alloys but in my experience
aluminium design stresses are normally quoted as 2% proof stresses not
yields. Aluminium alloys don't have an effective yield point as steel
does, they basically just snap without any warning which is why the 2%
figure is used. (I believe that this is defined as the stress that the
material is under when it has reached a permanant or plastic elongation
of 2%)

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