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Thread: Segmented Fork?

  1. #1
    DanBailey's Avatar
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    Question Segmented Fork?

    Fixin' to take a crack at a segmented fork. It's for a heavier rider (230 pounds). Using 7/8" .049 straight gauge (heavy rider, heavy fork, right?). I'm wondering if it doesn't make sense to drill a 7/8" hole through the steerer (1.125") and fillet braze a single cross-member through it. Yeah, I know, I've heard the warnings about punching holes in steerer tubes.

    At the same time, it's .049" wall tubing. Pretty heavy shit. And it's not like I'm not adding more material back, right?

    On the other hand, I'd prefer not to kill the user of the bike, either.

    I come to you, VS, for thoughts and advice.
    Dan Bailey
    Owner/Fabricator
    Pallas Athena Custom Bicycles
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    Andrew R Stewart's Avatar
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    Default Re: Segmented Fork?

    I'm no engineer but 7/8" diameter for the crown piece sounds small. And why you'd drill through the steerer?

    Check the archives for "segmented fork failure".

    My thought would be to internally sleeve the steerer, use a 1 1/4'x.058 crown piece and consider how to reinforce the top end of the blades. You probably know that a segmented fork will be heavier then a traditionally crowned one so the reason to do one is style. Or is there some other reason that we don't know of yet. Andy.
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    Default Re: Segmented Fork?

    welding looks better if it starts out cleaned | Flickr - Photo Sharing!
    this is 1.125" 0.058 4130 on the 1.125 steerer. It's going to be plenty strong.
    I overbuild this segmented fork with 1" legs 0.045 in some 1.125 0.058 sleeves.
    cheers
    andy walker

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    afwalker's Avatar
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    Default Re: Segmented Fork?

    I'm thinking also 7/8" is kind of smallish to resist torsional loads.
    1 or 1 1/8" seem better.
    The drill through is interesting, but we sure do miter and join tubes together and they seem to hold up fine.
    cheers
    andy walker

  5. #5
    Eric Estlund's Avatar
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    Default Re: Segmented Fork?

    Quote Originally Posted by Andrew R Stewart View Post
    internally sleeve the steerer.
    Be careful, you don't want to create an internal stress riser- I have seen forks brake this way.

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    Default Re: Segmented Fork?

    Quote Originally Posted by Andrew R Stewart View Post

    Check the archives for "segmented fork failure".


    You probably know that a segmented fork will be heavier then a traditionally crowned one so the reason to do one is style. Or is there some other reason that we don't know of yet. Andy.
    If you're thinking he'll find my failed segmented fork, the reason for it's failure wasn't drilling the steerer it was vent holes in the bottoms of the cross tubes. (so don't do that)

    A couple of reasons to build segmented are crowns may not be available to suit your particular application or the legs that fit that crown may not fit your application. For example, I don't think you'll find a traditional cast crown to fit a 26"x 4" tire, or fork blades long enough for a 29er fork. Also, disc brakes on curved 28x20 fork blades require some creative cutting to make the mount and I've heard several reputable builders question the durability of those blades for disc brakes.
    Of course, you can hit all those points with a unicrown too.
    Eric Doswell, aka Edoz
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    Default Re: Segmented Fork?

    Eric- Thanks for the reply. Yes, I'm referencing your experience. But not as a slight to you or thinking Dan, the op, will repeate the issues your fork had. More as a bumping him into rethinking his starting point. I also wanted to hear why he'd want to do so much more work if he was only going to duplicate what established stuff did. It is interesting how these methods/styles of fabracation seem to run in cycles. Your post of the fork's failing is for naught if no one sees it as we all go forward. Thanks for having the guts to share it. Andy.
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    Default Re: Segmented Fork?

    I getcha, I wasn't sure how clear your memory was on the project and thought maybe you thought I did what he was about to do. No biggie, I shared it so it could be a learning experience for many. That deal coulda gone down much worse for me, and if that post stops someone else from building a fork like that and getting hurt, I'm all for it.
    Eric Doswell, aka Edoz
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    Default Re: Segmented Fork?

    segmented forks still make me hesitate a little, but I walked around town and saw so many on cheap big box store bikes that I started feeling better about them. Working on one right now. I used 1 1/8" .058 crown pieces. I don't think I would go to a smaller diameter tube, the wall is probably not necessary. But since I'm brazing it to the steerer, it will not hurt much either.

    I don't think the steerer needs any reinforcement, any problem area is going to be somewhere on the crown and blades. Thought about using a sleeve on the outside of the steerer just to make the miter look better, but decided that didn't make sense.

    I suppose I should build a fixture to mount a fork on one of my fatigue machines, they aren't doing anything right now.

  10. #10
    DanBailey's Avatar
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    Default Re: Segmented Fork?

    Thanks, everyone, for the replies. I gave this all a LOT of thought during my drive home from the office, and the more distance I covered, the more it just sounded like a BadFuckingIdea(TM). I've got a bunch of 1" and 1.25" .058 sitting around, too, so that'll probably become my jumping off point. I've already got the stuff mitered for the 7/8" model, so I'll just build it up as a display piece.

    Thanks again for the feedback, guys. Much appreciated. If I can clear the funds to visit NAHBS this year (pending wife/CFO approval), I'll buy the lot of you a beer.
    Dan Bailey
    Owner/Fabricator
    Pallas Athena Custom Bicycles
    www.athenabikes.com

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