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Discussion Starter · #1 ·
So I have a little project that I need some advice on. I have a Carbon On One fork with a crushed leg. So my plan is to remove the carbon legs and replace them with either titanium or stainless tubes (KVA).

I already cut the legs out and removed the carbon bits from the dropouts and am working on the crown, which is a little more difficult because of a steel insert inside the carbon legs at the crown.

Anyway, I need advive on tubing spec's. First problem: the carbon legs are 34.0mm OD, not a commonly available tube size in the US. I have access to a lathe and can machine some inserts to use either 31.8 or 28.6 OD tubing. Although if the tubing gets too small it's going to look funny! Also what wall thickness should I be looking for?

The tubes will be bonded to the crown and dropouts with some kind of epoxy, depending on what material I end up with.

Any advice would be appreciated. BTW, I'm 190lbs and ride techy East coast stuff.

Thanks,
Mark
 

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You could just by a Salsa Cro-Moto and be done with it for probably less money and you'll get to keep your teeth. I mean, what's the plan here, just to glue tubing into the aluminum crown.
 

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Discussion Starter · #5 ·
jay_ntwr said:
You could just by a Salsa Cro-Moto and be done with it for probably less money and you'll get to keep your teeth. I mean, what's the plan here, just to glue tubing into the aluminum crown.
Thanks for the VERY encouraging post! Yes, the plan is to glue steel or titanium tubing into the crown and dropouts. It's obviously not that simple, which is why I asked the question. If carbon tubes can be glued, why not metal? It will require the right adhesive, which I have access to, and some way to work out the diameter differences.

What I really want to know is what wall thickness tubing would be appropriate for either titanium or KVA stainless in either 28.6mm or 31.8mm OD?

Mark
 

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Could be a fun slightly ballsy project.

I would work this angle.. figure out what epoxy you will use (may depend on leg material), and research it's needed gap between crown id and leg od. You should have a good idea of what diameter the legs will need to be at that point. The shim idea sounds dodgy to me.. more materials, more epoxy, more opportunity for the project to fail. Some carbon legs and steerers are epoxied *and* pressed. Figure out the correct gap for the epoxy for your given materials, and work back from that.. the gap is critical.

How'd you get the castings so clean?

-Schmitty-
 

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http://www.lotustalk.com/forums/f101/what-adhesive-used-bond-elise-chassis-71543/

There is some general info in this thread. 3M (i think) was pushing methacrylate on a company I worked for as an alternative to welding sheet metal. It was strong if applied properly, however could not take the heat of powder coating and required the metals to be stripped of all oil at the bonding step. This would not work for us as we powder coat the bulk of our products and it could be a day before the parts were finished. Properly prepping and applying adhesives is massively important and some can be pretty tricky. Also I have heard and had a friend or two have one of the early Trek frames that are kind of known to fail now due to corrosion caused by the dissimilar materials. Good luck and be careful.
 

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1.3mm

Assuming the legs stay in, if you don't want them to break, I'd use 1.3mm wall or thicker, at least at the top portion. That's strong enough (with 28.6 blades, in steel) for pretty stupid riding with a welded/segmented fork, anyway.

Note that I'm talking about 4130. I have never attempted to build a fork out of any stainless tubing, KVA or otherwise. Nothing in their stock part list looks even vaguely appropriate to me.

IMO, you'd be better off starting from scratch - that way you can select the components for a reason other than their fit with existing salvaged parts. Yes, it's a bigger job - but you have a chance of ending up with something good, instead of something mediocre at best, dangerous/crappy at worst.

-Walt

bikeny said:
Thanks for the VERY encouraging post! Yes, the plan is to glue steel or titanium tubing into the crown and dropouts. It's obviously not that simple, which is why I asked the question. If carbon tubes can be glued, why not metal? It will require the right adhesive, which I have access to, and some way to work out the diameter differences.

What I really want to know is what wall thickness tubing would be appropriate for either titanium or KVA stainless in either 28.6mm or 31.8mm OD?

Mark
 

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I've done something similar re: bonding tubing to aluminum, but I'd go with carbon tubing again. That will make galvanic corrosion a non-issue for a bi-metal fork, given that the epoxy is likely to have some sort of conductivity.

Epoxy is Loctite Hysol 9430. You need to acid etch the aluminum in order to properly prep the surface for bonding, and will need to plan on a bond gap of around .007 inches. This epoxy needs 5 days to cure @70 Fahrenheit. The tubing fails before epoxy in every test we performed in tension and compression.

Here's a link on how to go about it:
http://www.carbonfibertubeshop.com/cut & bond.html.

If you're not considering carbon, then disregard this post.
 
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