where's scientific altruism when it's needed eh?
When you pay us properly we'll work on it.
Bike Forum
Why are there no carbon stanchion forks?
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When you pay us properly we'll work on it.Posted 7 months ago # -
A carbon tube with a thin, kashima-coated aluminium tube around it.
Posted 7 months ago # -
And then another thin aluminium tube inside it to allow the piston/damper to seal?
So we're replaceing one thin aluminium tube with 2 thin tubes and some CF inbetween them, which were not quite sure how we're going to get in there?
There are stronger/harder aluminiums we could use and don't, so I'm guessing we've reached the point where the need for stiffness and strength are equaled by a certain material and trying to go any lighter/stronger results in less stiffness, a bit like trying to use 953 in MTB's.
Posted 7 months ago # -
I was joking about the aluminium tube.
Posted 7 months ago # -
<Yoda mode> Truth in that, there is...hmmmmm </Yoda mode>
Posted 7 months ago # -
Why are there no carbon stanchion forks?
I'm sure Al could bodge something together for you.
Posted 7 months ago # -
Getting the chemical resistance would be no issue. Maybe a vinyl ester resin or an epoxy novolac.
You could even polish them smooth but I think you'd be replacing them every ride as I don't think they would be resistant to the wear.
Maybe you could try some nano aluminium oxide in there and a good post cure regime. Still not convinced.
Does carbon composite get used on any other similar contact surfaces?
Posted 7 months ago # -
How about still having a coated alu stanchion but much thinner so it is basically a surface for sliding. The stanchion tubes can then be internally coated on carbon. I'm not sure how but I imagine you could pre-make a CF weave tube and then a bladder could be put down the middle,resin added and bladder inflated. The resin is then cured, bladder deflated and removed and you have stiffer and lighter stanchions.
Or maybe the outer alu sleeve could be header up then pressed over a carbon core before cooling?Posted 7 months ago # -
A lot of forks use the internal surface of the stanchions for the air/oil seals to work on so you'd need to do the insides too.
Posted 7 months ago # -
same reason they arnt made of Ti - carbon is flexy. that is the whole point of it
Posted 7 months ago # -
But they make lowers from carbon and they aren't flexible. Surely it's how it's made that makes something flexible?
Posted 7 months ago # -
Posted 7 months ago #
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Shock tech did carbon stations with a steel sleeve many years ago .iirc pace also did experiment with chrome plated carbon ,this was when chroming or getting any kind of wear resistant coating to stick was hard.
A compound carbon tube would be great but there's the cost of doing it, however when a fork can cost 800 big ones maybe it would just be a step too farPosted 7 months ago # -
You don't get carbon used much in bearings either!!! an obvious reason!! Carbon is soft and metals are hard! Fork stanchions pass through fork bushings, a bearing with very tight tolerance that must remain smooth... carbon pipes are not ideal for that as their surface is too soft....
Posted 7 months ago # -
carbon is flexy. that is the whole point of it
Yes - that's the reason lots of bike parts are made from carbon, everybody likes flexy frames
Posted 7 months ago # -
The carbon/aluminium sandwich suggestions are not that outlandish - carbon/aluminium and carbon/titanium stacks are pretty common in aerospace these days. Thay are however expensive and difficult to make and machine.
Carbon wouldn't survive the temperatures required for ceramic or diamond coating, even if you could get it to bond in the first place.
Posted 7 months ago # -
pretty sure I could knock you up a resin for this. Spent 6 years working on something for a far more aggressive environment than mtb forks.
Just need to find about £40k for my new lab as I am now going it alone. Feeling flush?
PS interesting idea. I think work also needs to be done on the bushings.
Posted 7 months ago # -
PEEK is one of the best engineering polymers around, might be applicable. Dear though.
Posted 7 months ago # -
How about using TI tubes that are build using an RP type process with an internal structure? I'm certainly no expert but have seen some drawings of cranks build in such a way and according to the numbers thay are lighter and stiffer than alu.
Posted 7 months ago # -
what's an RP type process?
Posted 7 months ago # -
The RP is rapid prototype, it a method that builds a structure from powdered material (think toner in a printer), this can allow for much more 'creative' structures that aren't possible when working back from a solid lump of material. As I say I'm no expert so it'd be interesting to hear an engineers view??
Posted 7 months ago # -
RP stuff is effectively a pretty crap sinter? Good for making prototype shapes, but prety crap mechanicaly surely? Would have none of the strength of forged components (or drawn tubes)? Otherwise we'd sinter everything rather than messing arround with drawing tubes/hydroforming/welding.
Posted 7 months ago # -
RP stuff is effectively a pretty crap sinter? Good for making prototype shapes, but prety crap mechanicaly surely? Would have none of the strength of forged components (or drawn tubes)? Otherwise we'd sinter everything rather than messing arround with drawing tubes/hydroforming/welding.
This was my take on it when I actually looked at it for a complex production item - unless the geometry is so hideous that you can live with the reduced properites you still need to live with the machining costs from 'real' material
I was thinking about this on the way home last night and I do recall see a paper at a conference where a polymer and application process has been developed to adhere to CF wings to act as a hard/low friction coating as an anti-ice solution. How hard and how low friction would be the key, but maybe Stoner can have his moon-on-a-stick after all
Posted 7 months ago # -
Why are there no carbon stanchion forks?
...it'd be interesting to hear an engineers view??
Because it's a daft idea, expensive to execute*, with very few benefits.
however, if someone does it, i'm sure they'll sell, cos 'carbon' is just better - everyone knows that.
(*some of the composite geeks here at work have a very similar project)
Posted 7 months ago # -
I think drawing tubes for production tubing is vastly cheaper, especially in high volume. This article is about bone tissue engineering but is worth a read as I believe the same tech is used in F1, aerospace etc
I don't think creating a sufficient structure is a problem, it would be cost.
Posted 7 months ago #
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