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  1. #1
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    Tubing Size For Linkage Fork?

    I want to build a linkage fork. I will use steel tubing for the legs to see if my idea works, and because I cant weld aluminum. I realize I will have a HEAVY fork.

    I was thinking of using either 1 1/8 or 1 1/4 round tubing with either a .90 or .125 wall thickness.

    Will these sizes work, or is there something better/lighter I can use? Maybe a thinner wall thickness? I weigh 225lbs and the fork will have 3-4" travel, and will be setup with a 203mm disc brake.

  2. #2
    WIGGLER
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    Girvin style or AMP linkage fork? The tubing diameters seem OK but the wall thickness
    Might be a little overkill, with .90 or .125 wall the fork would weigh as much as or more
    Than a complete bike.
    PAYASO 36er.....Live the Circus

  3. #3
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    It will be a Girvin style fork. What thickness would be better?

    I was thinking .090, but maybe .083 is better? Would .065 be too thin? Total length of the leg would be about 24" from the dropout to the top of the linkage.

  4. #4
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    If you have some existing metalworking skills and decent tools, you can easily use .035 and just reinforce/sleeve in some spots where you're joining the linkages. If not, use .049 or .058 or something, maybe? I don't think anyone here has built a steel linkage fork.

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  5. #5
    WIGGLER
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    So if the total length is 24 inches the lower link would be about 6 or 7 inches lower
    So contacting the fork leg about 17 or 18 inches and if you tab off the legs or barely
    Cut into the leg at the lower link height minimum .058 1-1/8 and .049 1-1/4 is what
    I would use if I was doing it maybe thinner if it was for me or if you trussed it let say
    Springer fork or jones style
    PAYASO 36er.....Live the Circus

  6. #6
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    I have a fair amount of metalworking skills. Mostly from automotive work. I've done custom suspensions on classic cars, and I've done sheet metal work. Im used to doing cars, where weight isnt an issue and overkill is good.

    Ill go with .058 or .049. Thanks for the information!

  7. #7
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    Thanks for the tips! here is a link to the fork build.

    Fat VS MTB Fork Geometry

  8. #8
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    I would be very concerned about the crown there. How big are the holes you tapped for the bolts?

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  9. #9
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    The holes are 1/4-20. Any suggestions are greatly appreciated.

  10. #10
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    here is prior example of similar project;
    Custom Noleen Fatbike Girder Fork

  11. #11
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    Quote Originally Posted by blown240 View Post
    The holes are 1/4-20. Any suggestions are greatly appreciated.
    yeah, anything you can do to take the shear stress off those bolts would be good. I've done some strength tests on various bolts in school and the results may surprise you. Not all that strong in shear or tension, especially those black class III ones.

  12. #12
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    The bolts into the crown are hardened steel shoulder bolts. The crowns will break first.

  13. #13
    Randomhead
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    a shoulder bolt is intended to take shear on the large section, not the threads.

  14. #14
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    True. I have the shear point on the large section. Thanks!

  15. #15
    Randomhead
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    I couldn't tell from your pictures, so the shoulder goes into the crown pieces in such a way that the vertical load is transfered to the crown pieces through the shoulder?

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