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  1. #1
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    Headtube reaming a factory frame?

    I posted this on the general forum, but think that it is more of a frame-building question

    The bottom of my headtube has an internal diameter or 44mm, and na external diameter of ariund 65.5mm

    I would like to fit a headset with a bottom cup OD of 54mm

    The bottom of the headtube has a wall thickness of around 10.5mm

    Can I ream/bore the bottom ID to 54mm to fit the headset?

    The frame is constructed from Al6061T6
    The dimensions listed here are not exact, would obviously need to have everything within tolerance

    What are your thoughts?

  2. #2
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    You should just get the proper sized headset cup.

    1cm thick head tube, Are you sure? That seems crazy thick even for aluminium are you sure it is not just thick at the face (i.e. hourglass shape).

    In any case, reaming is not the way to enlarge holes and not recommended for this much material removal. Getting the proper sized headset cup is the way to go.
    Mark Farnsworth, Raleigh, NC
    http://farnsworthbikes.com

  3. #3
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    The headtube is tapered, and yes it is an hourglass shape, but with a wider bottom than top.

    The top of the headtube has ID 44 and OD 55

    The bottom was only opened to 44mm to fit the 1.125inch steerer that came with the model - other models with the same frame came with tapered steerers, 1.124 - 1.5
    I assume that the same headtubes were opened to 54mm to accomodate the tapered headsets OD of 54mm

  4. #4
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    It's not an insert?

    There's just no sane reason to make a 10mm thick head tube just so you can miter the same complicated miter as your tapered steerer bikes.
    Last edited by dr.welby; 3 Weeks Ago at 08:04 PM.

  5. #5
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    Im with DR Welby are sure it's not an insert reducer maybe post up a pic so we can see!
    PAYASO 36er.....Live the Circus

  6. #6
    The cat's name is jake
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    What is the brand/model of frame, out of curiosity?

    The headtube would best be modified with a milling machine capable of circular interpolation (CNC without enclosure, or a K&T 2D, in the unlikely event you knew someone with one of those), then reamed to finish size. A reamer would not be able to handle that type of cut. It could be done incrementally with a boring head in a manual mill as well. If you tore the frame down, figure on an hour+ to machine a plate to use as a cap to fixture the head tube on the mill table, and another hour + to machine the headtube. Figure between $65 and $125/hr for machine work.
    Last edited by BungedUP; 3 Weeks Ago at 08:03 PM.

  7. #7
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    Frame is a scott spark 29er team 2012. This model comes with a straight steerer fork, higher spec models come with tapered steerer forks.

    Here are some pics:
    Looking down into the headtube
    Headtube reaming a factory frame?-20140703_092213%5B1%5D.jpg

    Looking from the bottom. The ring is the flange of the headset, not a spacer
    Headtube reaming a factory frame?-20140703_092202%5B1%5D.jpg

    Front view of frame
    Headtube reaming a factory frame?-20140703_092151.jpg
    Side view of frame
    Headtube reaming a factory frame?-20140703_092141.jpg


    View from the bottom. Paint has been sanded away to check if there was a spacer that had been painted over
    Headtube reaming a factory frame?-magnifier_20140702_190636.jpg

    Close up from the top,
    the black inner ring is the top of the lower cup,
    the headtube then has a radius from ID 44mm to ID 54mm, followed by a taper out to about 57mm
    Headtube reaming a factory frame?-magnifier_20140702_190245.jpg

    I have a milling machine, so using a boring head would be the preference.
    Plan on using a dial test indicator to centre/align the milling head to the current hole in the headtube.

    However I am not sure how to secure the headtube (with frame attached) to the mill - hoping to get some help with this part!?

  8. #8
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    Quote Originally Posted by BungedUP View Post
    What is the brand/model of frame, out of curiosity?

    The headtube would best be modified with a milling machine capable of circular interpolation (CNC without enclosure, or a K&T 2D, in the unlikely event you knew someone with one of those), then reamed to finish size. A reamer would not be able to handle that type of cut. It could be done incrementally with a boring head in a standard mill as well. If you tore the frame down, figure on an hour+ to machine a plate to use as a cap to fixture the head tube on the mill table, and another hour + to machine the headtube. Figure between $65 and $125/hr for machine work.
    Cap fixture could be the solution for securing it - what exactly do you have in mind?

  9. #9
    The cat's name is jake
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    Take a piece of plate larger than the diameter of the hole you need to make by 2"+ in all directions, drill 3 or 4 holes in it for your stud hardware (to clamp to the table), bore a hole for access to the headtube, and sandwich the headtube between the mill table and the plate. Obviously, you'll need to plan out where the stud hardware holes are in relation to the table slots or bolt pattern (if you use a sub-plate), and the clearance hole.

    You may need to space the bottom up from the table a tad to clear the top tube, if there isn't much extension of the headtube. You'll get it figured out when you start setting up.

    Watch out that the taper of the HT doesn't cause you trouble - if you bore it deep, you may start to thin the wall down quite a bit as you move into the external taper.

  10. #10
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    why don't you just run an external cup on the bottom?

  11. #11
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    Quote Originally Posted by adarn View Post
    why don't you just run an external cup on the bottom?
    The new fork is raising the front a bit, don't want to raise it any more with an external cup

  12. #12
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    Quote Originally Posted by Danielmessem View Post
    The new fork is raising the front a bit, don't want to raise it any more with an external cup
    Hmmm, well a cane creek EC40 will run you like $30, it might be worth running that for a bit to see how it handles before hurting the frame.

  13. #13
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    Quote Originally Posted by adarn View Post
    Hmmm, well a cane creek EC40 will run you like $30, it might be worth running that for a bit to see how it handles before hurting the frame.
    Can't argue with that - lets see how she handles

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