aluminum frame

Hello again, I was looking on the web at the carbon fiber unis and wondered if
anyone has made an aluminum frame for a unicycle. All that I have seen are steel
or some sort of Chrome alloy i think. Would aluminum be strong enough? One
advantage would be that it wouldn't rust. thanks again, Jeff
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[color=blue]>[/color]
[color=blue]> Hello again, I was looking on the web at the carbon fiber unis and wondered if[/color]
[color=blue]> anyone has made an aluminum frame for a unicycle. All that I have seen are[/color]
[color=blue]> steel or some sort of Chrome alloy i think. Would aluminum be strong enough?[/color]
[color=blue]> One advantage would be that it wouldn't rust. thanks again, Jeff[/color]

Sounds workable to me. Some of the aircraft grades of aluminum are very strong.
I believe some rims are also made of aluminum.

Lowell yoda@socket.net

Scott Bridgman (AKA The Muniac) made an aluminum muni and he brought it to the
2000 California Muni Weekend in Tahoe. It was custom made by him (he's a
machinist). I'm not aware of any other aluminum unicycles although I'm sure
there must be at least one other aluminum unicycle out there.

john_childs

[color=blue]>From: jeff d tuttle[/color]
[color=blue]>[/color]
[color=blue]>Hello again, I was looking on the web at the carbon fiber unis and wondered if[/color]
[color=blue]>anyone has made an aluminum frame for a unicycle. All that I have seen are[/color]
[color=blue]>steel or some sort of Chrome alloy i think. Would aluminum be strong enough?[/color]
[color=blue]>One advantage would be that it wouldn't rust. thanks again, Jeff[/color]

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On 11 Nov 2000 20:40:41 -0800, yoda wrote: <someone else wrote, but I don't know
where the attributioj went>
[color=blue]>>[/color]
[color=blue]>> I was looking on the web at the carbon fiber unis and wondered if anyone has[/color]
[color=blue]>> made an aluminum frame for a unicycle. All that I have seen are steel[/color]
[color=blue]>[/color]
[color=blue]>Sounds workable to me. Some of the aircraft grades of aluminum are very strong.[/color]

Not as strong as steel. Aluminium is used in aircraft because its specific
strength is high. That is, it's weaker than (most) steels, but its
strength-per-weight is good. So, a bit of aluminum is bigger than the bit of
steel of the same strength, but it's also lighter.

Where aluminium is less good is that it's a _lot_ less stiff. The aluminium
piece, though as strong, will be less stiff. You overcome this by modifying
the geometry.

To make an aluminum tubular element that performs as well as a steel one you
make the aluminum tube wider diameter. This introduces more material, so that
overcomes the fact that the aluminium is less strong. However, when you balance
the strength that way, you find the aluminum is still more flexible. To overcome
that, you make the tube even bigger diameter, but make the walls thinner. You
then have a tube that's the same strength and the same flexural stiffness, but
you discover that the aluminium tube is lighter than the steel one. This is what
cannondale do with bikes - it's why their tubes are much wider than the tubes in
a 'normal' steel bike frame, but the frame is lighter.

But there's a down side - to actually balance things out, your aluminium tube
has very thin walls - and is not that rugged. The tube as a whole might be
strong and stiff, but the walls are so thin you'd be able to dent them by
squeezing with your hand. Then all sorts of secondary effects appear and you're
in troble. You can demonstrate this with an empty coke can - while it's intact,
if you're careful you can stand on it. Put a small dent in the side, and when
you try and stand on it, it collapses.

The other down side is that aluminium is a pig to weld. You need to adopt
specific methods, and it's probably best to heat-treat the assembly after the
weld (back to cannondale - they heat-treat the whole frame after it's been
assembled). Increasingly, it's easier to glue.

One red-herring that people will produce for steel versus aluminium is the
'fatigue limit'. I'll not describe it, but though it is technically true, it's
not relevant to a properly designed bicycle or unicycle frame.

Since the weight is not that big an issue with a unicycle frame, and since it's
beneficial to keep the tubes small diameter, and since the frame needs
ruggedness as well as strength, I'd not think aluminium is worth the effort for
a unicycle.

[color=blue]> I believe some rims are also made of aluminum.[/color]

All decent bicycle wheel rims are made of aluminium.

regards, Ian SMith
--
|\ /| Opinions expressed in this post are my own, and do
|o o| not reflect the views of Amos, my mbu puffer fish.
|/ \| (His view is that snails are very tasty.)
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[color=blue]> Scott Bridgman (AKA The Muniac) made an aluminum muni and he brought it to the[/color]
[color=blue]> 2000 California Muni Weekend in Tahoe. It was custom made by him (he's a[/color]
[color=blue]> machinist). I'm not aware of any other aluminum unicycles although I'm sure[/color]
[color=blue]> there must be at least one other aluminum unicycle out there.[/color]

Also, Scott's MUni is very light, and the frame looks bombproof. No worries
about thin walled tubing on this one! I have a picture of it on Ofoto:
www.unicyclin.com/ofoto, MUni Weekend 2000 And Scott probably has pictures on
Muniac.com as well. It's a very impressive unicycle.

But of course it's not the first. I just bid on one on eBay. This auction is
over and I lost, but you can probably still see it:
http://cgi.ebay.com/aw-cgi/eBayISAPI...tem=1100009867 This is almost
guaranteed to be aluminum. I've seen some similar ones as well, also home made.

Stay on top, John Foss, the Uni-Cyclone http://www.unicycling.com

"Sometimes there just aren't enough rocks." -- Forrest Gump