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  • Drilling cranks for Dual holes

    I've seen examples of Kooka's with multiple drillings, and I started thinking about if there were any cranks around that could be "dual holed."

    I am interested in a pair of cotterless cranks for a road/very light XC uni. I already have a UDC CrMo hub, and for what I intend it doesn't seem necessary to go with ISIS. Except that I like the idea of dual hole cranks.

    The photo's of the Nimbus Venture cranks look like they might have some room to drill a second set of holes, or the Pro-Wheel 150's maybe.

    I saw that PDC had a machinist do the work on the Kooka's, and it looked really nice. If such a high quality finish wasn't that important what would the process be for doing a job like this in the garage?

    What I'm imagining is a jig that screws into the existing pedal threads, and has a clamp that centers the drill guide on the crank arm in the same way that a doweling jig works. There would be a pin that threads into each crank which indexes the drilling guide so that the distance from the original hole would be consistant on both cranks. Then the drilling itself would be done slowly with a hand drill, and plenty of cutting oil.

    The trick then would be tapping the new holes. I am going to check with my LBS to see if I could use their crank taps, or what they would charge to do the tapping for me.

    Back when I was working in a shop we occasionally had to drill out stripped cranks, and put Helicoils in. The tapping phase of this project should be about the same as that.
    "A properly ridden unicycle is like an object in orbit: constantly falling but never landing." -Diogenes

  • #2
    I think that it would be a doable job with a reasonable drill press. The holes must be parallel or it will behave badly. You could probably set up a jig to position the hole correctly. Using the drill press and a guide, you could center the hole accurately. I would not attempt it with a hand drill. It could be done, but it would be hard to do well.

    You would need both a left- and right-hand tap of the appropriate size. The left-hand tap is a specialty item I am sure you can find but it may not be cheap. What is the thread for standard pedals anyway?

    I have the equipment to do it except for the specialty taps.

    If I wanted to do it right, I would set it up on a milling machine, which I do not have. This would allow you to get the position perfect. It is an easy job on a milling machine. This is the type of equipment you might find in a high school machine shop.

    Good luck with your project.

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    • #3
      I teach high school art, and now that you mention it, we have a small CNC mill in our tech lab. It would be big enough to drill these holes.

      I have a drill press, but I was thinking that if the jig was done well, it might be easier to align the drill with a hand drill. But if I get my drill press vise in just the right spot, and have the table set close to the head to minimize quil wandering I think it would be a good way to go.

      The threads for standard pedals is 9/16"x20tpi. It is a fairly special tap on both sides, but especially so on the left. A lot of good bike shops have these taps for cleaning/chasing pedal threads. If you want to buy them I think you can get a set for around $20-$30, but I think that my LBS would either let me use their taps, or charge me to do the work. Either way it should be much cheaper than buying taps I won't be using again.
      "A properly ridden unicycle is like an object in orbit: constantly falling but never landing." -Diogenes

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      • #4
        I think that the prowheel cranks would be a better choice for drilling than the nimbus cranks. The prowheel cranks concentrate their metal on the outside of the crank while the Nimbus cranks look like they concentrate the metal in the center.


        You might have to fill in a bit of the grove in the back if the hole is too far down the crank. I remember seeing pictures where someone did this here.


        For ISIS cranks the Qu-Ax cranks look about ideal. The cotterless version seemed to have disappeared.
        My friends, love is better than anger. Hope is better than fear. Optimism is better than despair. So let us be loving, hopeful and optimistic. And we’ll change the world. - Jack Layton

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        • #5
          I got a machinist to drill my 150mm pro wheel cranks with a second hole (at 110mm) but they failed on my first serious hill climb- ie bent and twisted etc. So unless you can get some Kooka's done properly or are keen to go to an ISIS with a double hole moment set up i would think it over and be prepared for an annoying failure.
          mark
          Find out about my latest Enduro XC rides and races at my blog.

          http://www.markandhisunicycle.wordpress.com

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          • #6
            So it sounds like the pro-wheel cranks aren't up to it. The ventures seem like they might be able to handle it, but without seeing them, or seeing the dimensions of the arms it's hard to know for sure. I won't blindly get them and find out that they won't do.

            If anyone has a pair of the 150's and can measure the cross section at 125mm I would greatly appreciate it.
            "A properly ridden unicycle is like an object in orbit: constantly falling but never landing." -Diogenes

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            • #7
              Hey guys

              does anyone know what size drill bit I should use? 9/16" or maybe a tad smaller, like a 17/32"?

              I am planning of doing a few cranks soon.
              My friends, love is better than anger. Hope is better than fear. Optimism is better than despair. So let us be loving, hopeful and optimistic. And we’ll change the world. - Jack Layton

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              • #8
                Here is the the Park website:

                http://www.parktool.com/products/det...=27&item=TAP-6

                They suggest 33/64", but 0.5125" is the preferred hole size.

                Scott

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                • #9
                  You need to find the thread count of the pedal

                  Then there will be a recommendation, with the tap you buy, for the drill size.

                  I have my doubts about cutting threads into aluminum, when you plan to swap pedals a lot. My cheap aluminum cranks have held up ok, but I grease the pedals, then leave them in a real long time, till I bust them mostly.

                  That's a lot of work drilling and tapping to make a set of short lived cranks. I wouldn't bother with the dual hole crank idea on a non ISIS uni. If you really plan on swapping pedal positions often, get the 2 hole KH cranks with the steel inserts. That is why KH uses the steel inserts. You can only swap pedals so many times in aluminum threads before they strip. The KH option would be cheaper in the long run. And if you don't plan on moving pedals, what is the point ?

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                  • #10
                    I have the park taps

                    on the package it says that they are meant to "re-tap" dammaged threads and to clean up imperfections. No mention of tapping new holes.

                    I plan on tapping two 137mm KH cranks at 110mm as well as a double hole 137/165 at 110mm.

                    one of the 137/110s will be for a freestyle/trials
                    one 137/110 will be for a XC/road 26
                    and the 165/137/110 will be for a bombproof 36 ready for trial or road.

                    I might test on some cheeper Qu-Ax cranks first.
                    My friends, love is better than anger. Hope is better than fear. Optimism is better than despair. So let us be loving, hopeful and optimistic. And we’ll change the world. - Jack Layton

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                    • #11
                      I recently stumbled across this page where someone details a homemade jig for shortening and drilling cranks for their recumbent. Not sure if there's anything there that hasn't already been covered here but thought I'd share.

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                      • #12
                        Originally posted by saskatchewanian View Post
                        on the package it says that they are meant to "re-tap" dammaged threads and to clean up imperfections. No mention of tapping new holes.
                        I've used the taps to cut new threads before, but I wouldn't recommend doing so "free-hand". These taps only have a few threads of taper, so it's not so easy to line up. If you use the taps in the drill press / mill (with a live center) immediately after drilling the hole, you're good to go.
                        "The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt." - Bertrand Russell

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                        • #13
                          Thanks, I think I will do that. I never thought of using the mill to run the tap as well but I guess there is no reason that shouldn't work as long as I use lots of cutting oil.

                          33/64" seems to be a pretty tough drill bit size to find. I think I am going to try 1/2" even though that seems like a lot of material to remove.
                          My friends, love is better than anger. Hope is better than fear. Optimism is better than despair. So let us be loving, hopeful and optimistic. And we’ll change the world. - Jack Layton

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                          • #14
                            I have tapped in motorcycle parts before

                            I don't think you should use a drill press, except for drilling the hole. Turn the tap in by hand with a T handle until it starts to resist, then back it up a bit (to allow shavings to fall), then repeat, cut a bit, back up a bit, until you are all the way through. With a drill press, the chance that the tap will bind and snap, or that the treads will strip out, is high. In all the shops I have been in, we turned in the taps by hand with a T handle.
                            Attached Files
                            Last edited by feel the light; 2010-09-09, 02:28 AM.

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                            • #15
                              If you use a mill, you want to drill the hole and then use a spring center tap guide:

                              http://www.wttool.com/product-exec/p...nter_Tap_Guide

                              You mount this tool in the mill, and then bring it into gentle contact with the dimple on the hand tap wrench that feel_the_light posted. You proceed to cut the threads by hand, and the spring tap center keeps everything perfectly aligned.

                              This procedure is much better than cutting threads free-hand.

                              Scott

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