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Machining an accurate hole for bearing

Discussion in 'Downhill & Freeride' started by Nately27, Aug 28, 2005.

  1. Nately27

    Nately27 Monkey

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    I already posted this in Tech Talk, but since im under a deadline, I thought I'd get a better response here:

    I am trying to fit a 0.8750" O.D. bearing in a plate of aluminum, and the hole saw I have is naturally not accurate enough. I am thinking of using a hole reamer after cutting with the hole saw, because i have read these have an accuracy of less then a thousandths. This needs to get done before ill have access to a mill, so do you guys have any ideas? My questions on reaming a hole are: 1) if the hole is 0.860" will the reamer be able to take that much material off, 2) should i use a chucking reamer or a hand reamer? 3) are they really that accurate, 4)is there a better way to get the bearing in the plate? the bearing will not support much load, so thats not an issue, its just gotta have a snug fit to eliminate play yet not bind up the bearing. i will be able to cut a slot in some of the bearing supports so that they'll expand to fit the bearing, but this is not possible in all locations.
     

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  2. OGDMFG

    OGDMFG Monkey

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    BEHIND THE CLOAK OF HE ZION CURTAIN
    A Press Fit The Bearing Should Have A Press Fit Of .001-.002 Undersize.

    That Is The Way I Would Aproach It This Way

    J
     
  3. atrokz

    atrokz Turbo Monkey

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    Hi, I have some experience with this sort of stuff and I`ve gotten many a hole to tenth of a thou with no problems. You won't need that accuracy here but here`s what wil get you a top notch job done.

    First things first: make sure you have something that can clamp the part well, and evenly. A machinists clamp is much better than some EZ-Grip crap from Sears. Use the real deal.

    Second, make sure everything from the vise to the chuck is straight and even. Remember, even a small chip under the clamp can throw a hole off.

    Forget the hole cutter. it`s a joke and useless imo. Center punch the hole and use a center drill (a good investment anyways) to start the hole. Move up a few drill sizes to get closer to the .875. Reason for this is to not oversize the hole, which is problematic with drilling. 0.875 is a big bit, so there are some options to get it to this size. One is to actualy get a bit at .850 and this is what I would do. What ever you do, DO NOT use a .875 bit, as you are going to ream to get tight tollerances and drilling is allways oversized. A used .850 will probably get you a .860 hole unless it`s a well ground bit. Also, make sure all drill bits are in good condition.

    Then get a reamer (chuck is fine), as for size, I`'m not certain what ABEC class your using but I would try to aim for a .002 undersize. See if you can match that up.

    After reaming, chamfer the hole to aid in the bearing pressing.

    Oh, use a cutting fluid, and don't let anythign get too hot as it might mess up your tollerances ( I learn't the hard way).

    Lastly, the formula for cutting speed is 4 times (X) the materals cutting speed (aluminum is 150 I think? Dont have the handbook here so someone let him know) divided (/) by the diameter of the drill bit. For reaming and chamfering, put it much slower, at about half whats recomended in the formula.

    Hope that helps, good luck.
     
  4. Dunshee80

    Dunshee80 Chimp

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    just take it to a local machine shop if you have one. We made a floater for a friends bike, and needed the same thing. We had 3 locals shops that quoted us under $20
     
  5. atrokz

    atrokz Turbo Monkey

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    :stupid:
     
  6. Nately27

    Nately27 Monkey

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    Excellent...ive got a decent machinist clamp set up, ill have to look for a bigger drill bit, but ive found some reamers that are one thou undersize, so ill probably go with those unless I find something like 2 thou under. they're abec-1 bearings, with an OD tolerance of +0.0", -0.0004" so hopefully one thou under will work.
    I also might be able to get hooked up with a machine shop, it'd just be nice to be able to do it myself. 20 bucks is reasonable. but thanks for the tips guys.
     
  7. Nately27

    Nately27 Monkey

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    mayby ill look into a machine shop first! :thumb: