# Fork Bending ??? (on purpose)



## Fleas (Jan 19, 2006)

Disclaimer - I am not a frame builder.

Example would be the VooDoo Zombie 500 rigid fork.









Tapered Cro-Mo legs.

It has ~43mm OS.

If I want 50-55mm OS can I just bend it?

...or might I need heat?

I would figure to bend it below the bends to the crown and not close to the disc brake mount.

I realize it affects other geometry, but that little tweak should allow everything to fall in line with minimal compromise (at least on paper - I don't even have it in hand yet).

Would the bend cause work-hardening or something like that?

Thanks,
-F


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## GrayJay (May 16, 2011)

Bending CrMo fork blades is no problem, that is exactly how a framebuilder would add rake to a fork. You will need a jig/form to bend the blades such as: Easy Fork Blade Benders 
(google around for other designs too, a form made out of plywood is probably even easier to make depending on your tools and skills.)


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## Clockwork Bikes (Jun 17, 2006)

Those blades are really big to bend easily.


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## jgerhardt (Aug 31, 2009)

OS? Is that rake?
Ohh... Offset it just clicked.
Nm


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## dr.welby (Jan 6, 2004)

GrayJay said:


> Bending CrMo fork blades is no problem, that is exactly how a framebuilder would add rake to a fork. You will need a jig/form to bend the blades such as: Easy Fork Blade Benders
> (google around for other designs too, a form made out of plywood is probably even easier to make depending on your tools and skills.)


Since that's my Instructable I should probably mention it's not going to work to bend those blades anywhere near the top.


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## GrayJay (May 16, 2011)

For an existing fork, it should be possible to make a bending form design that holds fork via both of the dropouts and then slip a tight fitting pipe over the steertube and use that for leverage to bend the blades over the form. Would be best to use a very gradual arc form and add the bend over a long area instead of concentrating a sharper bend at one point. Large diameter tubes are much more likely to kink during bending than are smaller diameter road blades. To help prevent the tubing from kinking/crushing, fill the fork legs with water first and let them freeze to ice, helps support the tube during the bend.

Dont use heat to make the bend, that would weaken the steel more than just cold-setting.


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## heeler (Feb 13, 2004)

Don't let the bend get down towards the IS disc mount...


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## Fleas (Jan 19, 2006)

Clockwork Bikes said:


> Those blades are really big to bend easily.


^^^This I was guessing. I got a big lever. 

I was thinking of using the Park tool:









Yes? No?

Maybe I will give extra attention to the clamping/holding. I think I can make a wooden fixture to clamp the entire steerer, crown, and the tops of the legs, then use the Park tool against the fixture rather than against the fork leg. I can probably integrate a bend radius into the wooden fixture.

I like the freezing idea - that will help simplify the holding of the legs. I wasn't sure how I would get sand out of it or how I would hold the sides to avoid crimping it if I didn't use sand.

Thanks everyone for the reassurance.

-F


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## JaquesN (Sep 14, 2009)

Recently, I put a .035 wall, 7/8" cromoly tube in a (cheap) bender with a mandrel specific fr 7/8" tube. I put the bender in a vise and pulled as hard as I could on the handle of the bender (about 2 feet long). It did not budge. Then another guy in the shop stood facing me and pushed while I pulled. We bent the 1" handle of the bender. 

Point being, that stuff is really strong, and the walls of your fork are nearly twice as thick as the tube I was trying to bend.

You could try to find a local machinist with a good bender and a die small enough for the blades of that fork. It may be challenging to get both legs of the fork into the bender, though. 

I would not recommend the double-bender, grab the steerer approach. That would stress the weakest part of the legs, crown, or steerer, and it might not bend where you want it to.

Good luck with this project and let us know what happens.


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## Yogii (Jun 5, 2008)

Just braze or weld some forward facing dropouts on the front! You do even need to remove the existing ones!


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## Fleas (Jan 19, 2006)

I do not have the courage to bend a brand new fork.

Even if the geo. was horrible I'd have trouble doing it. As it is, though, the geo. feels pretty good. No fork bending happening here.

-F


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## BungedUP (Aug 18, 2003)

With the park tool, you can give the additional offset needed without too much trouble. There are 2 things that will give you a little trouble though:

1) You will need something to clamp the steerer tube very tightly that will not pivot or roll as you apply pressure. It can't crush the steerer though. You'll also need some way of rigidly holding that tool in place, to a bench, or vise. If you don't have the bench bolted down, it will most likely get moved with the force required to bend each leg separately. 

2) How will you measure the offset, and re-align the fork after you add additional offset? Without coming up with some additional tooling, it might be a bit tricky to do. However, if you insert a tube that fits well inside the steerer, you could use that as a reference for your steerer centerline. You'll want to check dropout alignment afterwards too, though it should be relatively good, assuming you don't twist the legs.


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## Fleas (Jan 19, 2006)

BungedUP said:


> With the park tool, you can give the additional offset needed without too much trouble. There are 2 things that will give you a little trouble though:
> 
> 1) You will need something to clamp the steerer tube very tightly that will not pivot or roll as you apply pressure. It can't crush the steerer though. You'll also need some way of rigidly holding that tool in place, to a bench, or vise. If you don't have the bench bolted down, it will most likely get moved with the force required to bend each leg separately.
> 
> 2) How will you measure the offset, and re-align the fork after you add additional offset? Without coming up with some additional tooling, it might be a bit tricky to do. However, if you insert a tube that fits well inside the steerer, you could use that as a reference for your steerer centerline. You'll want to check dropout alignment afterwards too, though it should be relatively good, assuming you don't twist the legs.


I had time to think this through before I decided not to do it.

We have a manual shop press at work for pressing bearings and stuff. I was going to make up some wood blocks to fit the fork crown and the fork blades (I would not use the steerer at all in the bending). I would clamp the dropouts in a carrier to keep them aligned, then just press the extra offset into the fork. The guy who suggested ice in the fork blades probably had the best suggestion to avoid kinking the blades.

The other option was to get 2 conduit benders, which we also have here. Clamp the dropouts in the carrier and go at it. This method would be more prone to over shooting the offset, though.

But, like I said, the bike looks too good, the handling seems fine, and the fork is out of production (no second chance).

-F


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