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PostPosted: Wed Feb 29, 2012 11:36 am 
Dirt Disciple
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Joined: Wed Jan 18, 2012 3:26 pm
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Location: London
I wouldn't recommend aluminium for something like that either, what about titanium? Should be more than strong enough and won't corrode to the aluminium like plain steel can.


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PostPosted: Wed Feb 29, 2012 12:13 pm 
Old School Hero

Joined: Wed Dec 14, 2011 9:57 am
Posts: 183
I have to ask: why? Are you wanting to use ano bolts or something?


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PostPosted: Wed Feb 29, 2012 12:29 pm 
retrobike rider
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Joined: Sun Sep 23, 2007 11:22 pm
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Location: Hove
This is not a serious question. Steel is far more dense than aluminium, so for a given volume of material it is far stronger. With frames, this doesn't matter because designers just specify thicker tube walls for aluminium than for steel, to end up with a tube that is equally strong because of the bigger volume of material, but lighter because it has such low density. However the volume of a bolt is obviously fixed, so all you have is something light but with nowhere near the strength that the designer felt was necessary. If you think the designer was an idiot, why trust his fork?

Add in that it is easy to round off an aluminium bolt if it gets stuck and there really is no case for them. Why do you want to save a few grammes from such a heavy fork anyway?


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PostPosted: Wed Feb 29, 2012 12:30 pm 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
Posts: 8209
Location: New Forest, UK
Andy145 wrote:
I wouldn't recommend aluminium for something like that either, what about titanium? Should be more than strong enough and won't corrode to the aluminium like plain steel can.


I've got corrosion on my Campag hubs' stub axles (alu) on my Litespeed, so Ti doesn't solve corrosion - you need plenty of copperslip on any Ti component on aluminium to stop corrosion. Any difference of metals is potentially a problem.

I have seen Alu boats where the bilge has corroded though in a neat circle due to a dropped 2p coin.

CP Titanium also is not great for cracking - so any cut threads (as opposed to rolled threads) are a potential source of cracks. I'll bet that Ti bolts use cut threads, due to the heat required to soften Ti.


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PostPosted: Wed Feb 29, 2012 2:29 pm 
Dirt Disciple
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Joined: Wed Jan 18, 2012 3:26 pm
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Location: London
hamster wrote:
Andy145 wrote:
I wouldn't recommend aluminium for something like that either, what about titanium? Should be more than strong enough and won't corrode to the aluminium like plain steel can.


I've got corrosion on my Campag hubs' stub axles (alu) on my Litespeed, so Ti doesn't solve corrosion - you need plenty of copperslip on any Ti component on aluminium to stop corrosion. Any difference of metals is potentially a problem.



I didn't know this, I had assumed Ti wouldn't react with metals around it. I found this on Stainless Steel World:

Quote:
Titanium should not be coupled directly to less noble metals, such as magnesium, zinc, and aluminium. These are likely to experience accelerated corrosion and, in the process, titanium may pick up hydrogen which is generated as the cathodic product of the corrosion reaction.


I'd better go and get the copper slip!

Going back to the original question, to be on the safe side the old aerospace adage 'Steel is real' applies.


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PostPosted: Wed Feb 29, 2012 2:42 pm 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
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Location: New Forest, UK
Yes, especially if you ever fit a bottom bracket or seatpost in a Ti frame.


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PostPosted: Wed Feb 29, 2012 9:02 pm 
Retro Guru

Joined: Mon Jun 02, 2008 2:52 pm
Posts: 347
Hamster, thank you. Something I had not considered and after some research looks like a very valid concern, in fact greater than the strength issue.


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PostPosted: Fri Mar 02, 2012 10:13 pm 
Old School Grand Master
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Joined: Mon Jun 14, 2010 9:06 pm
Posts: 4437
Location: Herts UK
Anthony wrote:
. Steel is far more dense than aluminium, so for a given volume of material it is far stronger.


denisty does not necessarily correlate to strength

rough rule of thumb:

Ti 1/2 weigh of steel but appriox same strength
Al 1/3 weigh of steel but appriox 1/2 strength *
dunno what the number are for carbon fibre.

(* some alloys comp retty close to strngth of steel)

So there are weight saving to be made, but to make an alloy bolt smae stength as the steel one you are replacing would mean it has to be larger diameter, maybe M8 or M10..

anyways, my 3 rules of weighweenieing are:
1. can it be made lighter?
2. how much will it cost?
3. if it fails what are the consequences?

1. and 2 are knowns so with 3, you need to consider what will occur if the bolt on the braces give way. The forks should be designed that the bolts stop the stanchoins from dropping out so unless you get some big air, nothing bad is gonna happen, nebvertheless, I wouldn;t do it.

I am using alloy bolts for shifters, brake levers, gear wire clamps but not for holding disc brake rotors or anything that is safety critical like stem or seat post ....


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