extending fork/steerer threads?

Discussion in 'BIKE TALK' started by ParkRNDL, Feb 17, 2019.

  1. ParkRNDL

    ParkRNDL

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    ok, so I want to rob the fork off a derelict girls' 24" Collegiate to use on a 20" Scrambler tribute. the head tube on the Collegiate is 6" at the outsides of the races, the Stingray/Scrambler is 4.75", so I wll need to add 1-1.25 inches of thread below what is already there. I saw where in this thread, both @The Renaissance Man and @GuitarlCarl referred to using this little unit or one like it. For that price, I am thinking about buying one and trying it myself. What all do I have to know before diving in? I assume I will also need something like this to make it work?

    Then assuming that I successfully thread the steerer further down, I guess will need to cut an equal amount off the top of the fork threads. I vaguely remember doing this with a hacksaw as a kid, following someone's advice to thread the top headset cone on all the way down first so that I could back it off and clean up the threads that the hacksaw boogered up. Is this the right way to do it, either with the headset cone or the die?

    thanks for any advice/insight...
     
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  2. Duchess

    Duchess

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    Yes to all. One more pointer would be that, to make it easier to cut perpendicularly, you can use some headset spacers or another headset nut as a guide (as it may get chewed up a little, I'd use a spare).

    When cutting threads, use plenty of oil, make about a half-turn or until it starts to feel tight, then rotate it backwards a little to clear the thread, and continue like that.
     
  3. GuitarlCarl

    GuitarlCarl

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    I've seen old dies that are a hexagon and can be turned with a big cresent wrench. But if you have a modern pipe die cutting set handy (round) you'll see that the handle for it is pretty big. The round one like above is nicer than mine, with the set screw tightener/loosener. But note that there are sizes for pipe and there are sizes for bolts / screws and they don't interchange. So do a little research and know your thread and die size.

    Carl.
     
    Last edited: Feb 17, 2019
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  4. The Renaissance Man

    The Renaissance Man __CERTIFIED DIVER__ (Open Water & Open Dumpster) Pro Member

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    Make sure your fork tube is not swelled out from either an over tightened stem or freezing.

    Instead of a handle,I ground flat spots on the side of my cutting die and locked in in my bench vice. Then turned the fork instead of the tool. The handle would be better though for that price.

    Use a nut and washer as a cutting guide as suggested by @Duchess
     
  5. Starnger

    Starnger

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    I'd usually just cut it below the thread and take the piece off, then weld :D
    This is probably not the proper way to do that, but till now all the forks i have done hold well. The advantage of that method is that you can also extend the fork, not just shorten, and it also works with thread-less :D
     
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  6. us56456712

    us56456712

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    I just grind a flat spot on the die and put it in my bench vice. I use a breaker bar to turn the fork but a crowbar works too. Works great. Put the race on before you cut it off as the threads will be goobered up from the cut and when you back off the race the threads will be corrected. Go slow and go backwards and then a little deeper forward and repeat. I would get a 1 1/2 inch and a one inch die at the same time.
     
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  7. RustyGold

    RustyGold

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    Everything above works fine. I would definitely go with a die-holder, it holds with out distorting the die. Also, the two handles allow you to put even pressure on the die so you are more apt to get it started straight, and stay straight.

    To help with straightness, extend the threads first, before cutting to length. It would be very hard to get crooked if you are fully engaged on the existing threads when cutting the new threads. You can leave the die on when cutting to length...chamfer the cut end (belt sander, grinding wheel, grey wheel, angle grinder, etc), and then back the die off to clean everything up.

    To help with die life...use a cutting fluid. If regular oil or penetrating fluid is all you have on hand, that is far better than nothing.
     
  8. ParkRNDL

    ParkRNDL

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    It's only been, what, nine months? But at any rate, I just pulled the trigger on this order:
    Annotation 2019-11-10 215313.png
    I will be sure to fill you all in on how it works out. Or doesn't, as the case may be. :grin::rofl:
     
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  9. Phil Fink

    Phil Fink

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    1. Sometimes one can get a deal on an adjustable die, that way you may cut away as little material as possible; also if there are any slight bulges, it might help, a little. Others have described cutting a minimum on the 1st downward cut, and then cutting slightly deeper in a 2nd cut while backing the tool off.
    2. Also, a fork may have extra threads, to the order of fractions of inches x 24; you may do some more math and figure if you can get by cutting many fewer threads. Why add threads that won't be used, and only weaken the part. It is a good idea to use a stem long enough so that the expander as far below the cut threads as will fit.
     
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  10. ParkRNDL

    ParkRNDL

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    That was quick...
    20191114_185639.jpg
    Now I need to buy thread cutting oil and work up the nerve to thread this thing on. It looks like it's a bomb squad job just to get this thing threaded straight on the existing threads, never mind cutting new ones.
     
  11. Duchess

    Duchess

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    It might be easier to start threading the die without the handle.
     
  12. RustyGold

    RustyGold

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    The handles make it way easier to see if you aren't straight. If you have existing threads, you should be golden. :thumbsup:
     
  13. Duchess

    Duchess

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    It's easier to see if it's going straight, but when starting a fresh cut, I personally find it easier to keep it straight by feel without the handle. I don't know if I put a twist on it or what I'm doing wrong, but I found that method works for me. It's not something I do all the time, so that's probably also a factor. Anyway, with existing threads, he should be fine with whatever he does.
     
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  14. GuitarlCarl

    GuitarlCarl

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    Keep the die oily, quarter turns back up an eighth and then a quarter turn more, takes a while and gets tougher once you're clear of the threads. Depending on the brand I'm sure but you'll most likely be taking more metal off the head tube than you would just threading regular black pipe so take it easy and keep it oily.

    Carl.
    (I don't have a handle but I use a large pipe wrench)
     
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  15. ParkRNDL

    ParkRNDL

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    @Duchess and @RustyGold: I had thought about putting the die on first, but i definitely see the point about the handles making it easy to gauge angles. I hope to play with it some today. First order of business is to get thread cutting oil at Harbor Freight. Thanks @GuitarlCarl for the lube and pacing advice; that's the kind of thing I need to know.
     
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  16. ParkRNDL

    ParkRNDL

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    Yeah so this cutting threads business already isn't going well. Are Schwinn headsets/threads bigger than other brands? Because something seems weird...

    The bright blue fork is the Schwinn 24" that I need to extend the threads on. The other one is a junker Murray or Columbia that I was going to practice on. 20191116_212435.jpg
    I assumed they would use the same size hardware. I'm not 100% sure that's the case.
    20191116_212527.jpg
    20191116_212615.jpg
    The adjustable cone off the junker was VERY tight on the Schwinn threads, like I couldn't thread it on by hand more than a few turns down the steerer tube. The Schwinn cone, on the other hand, seemed really loose on the junker fork:
    SmartSelect_20191116-223948_Gallery.gif

    So when I started playing with the die, I was able to thread it by hand most of the way down the steerer threads of the junker. But I couldn't seem to get it started correctly on the Schwinn; it just seemed like the threads were wrong.

    I did use this: 20191116_222925.jpg
    Any ideas?
     
  17. Duchess

    Duchess

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    I'm not a Schwinn person, but I do know they did their own weird stuff with wheel sizes, so it doesn't seem out of character that they did something similar with forks.
     
  18. GuitarlCarl

    GuitarlCarl

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    I've had compatibility issues with Schwinn before. Those two pieces are probably at the opposite ends of the tolerance spectrum, so they're technically the same size but Schwinn is not gonna have any play... But that's just my wild guess.

    Carl.
     
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  19. horsefarmer

    horsefarmer

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    Well the outer diameter is only .007" smaller on the cheap fork so thats probably going to introduce some slop.

    The real issue is that threads don't ride on the outside diameter of the tube and the inside diameter of the cone, they ride on the pitch diameter of the threads and this determines the "fit" of the threads.
    pitch diameter.jpg
    This is the distance from a point on the screw thread to a corresponding point on the next thread measured parallel to the axis. Pitch Diameter is the simple effective diameter of screw thread, approximately halfway between the major and minor diameters.

    There should be an adjustment screw on the die which will spread the die open a tiny bit. This will increase the pitch diameter and the cone will fit tighter. I would open up the die some then run it down the junk fork threads and cut a few new threads farther down the tube then check the fit of the cone there.
    adjustable die.jpg
     
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  20. ParkRNDL

    ParkRNDL

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    Ahhhh, interesting. The problem is that I bought a cheap die that's not adjustable. I did see them in some of my reading and research, but the solid ones are what popped up when I searched Fleabay.

    I'll check with a friend here who has far more experience with this stuff and might have a split die. (I could have probably just borrowed the tool from him to begin with, but I thought it'd be cool to have one myself. Can't have too many tools, ya know. :grin: )
     
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