Making a disc or Boxpok driver

Mark St Clair Jul 21, 2021

  1. Mark St Clair

    Mark St Clair TrainBoard Member

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    I posted this on the N Scale forum and thought I might get input here on the modern tools forum, too. Hope posting in both places is OK.

    Some of you know I have been modifying a Kato Mikado over the past year or so. Along the way I have been learning, and re-learning, both vintage and modern modeling skills. Here is my current challenge. Making a driver like this drawing:
    [​IMG]

    The starting point is a standard Kato main driver:
    [​IMG]

    I have not found an off-the-shelf solution. Kato JNR prototypes have different designs. If there is an available overlay or insert, I have not seen it.

    Two questions.

    1) How would you do it? Please provide as many specifics as you can.

    2) What are the other appropriate forums to post this question in addition to N Scale?

    Thanks in advance.

    Stay safe,
     
    gmorider likes this.
  2. Mr. Trainiac

    Mr. Trainiac TrainBoard Member

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    Modeling a boxpok driver and 3D printing it through Shapeways or on a personal resin printer would be pretty straightforward, but my main concern would be getting everything true and centered. A 3D printed part may need a bit of cleanup, and an imperfectly reamed axle hole would result in an off-center driver and a wobbly locomotive.

    Actually designing and printing the wheel is the easy part, getting it to operate well on an N scale model is a bit harder.

    For a scratchbuilt driver, an overlay would be difficult to do on the Kato spoke driver. You may need to remove the tread and sand the face flat to give yourself a recessed surface to add a new styrene face. I think adding the 'poks' without modifying the core would result in an overly thick wheel. The wheel face on a Boxpok driver is not flat either. Most photos I have seen show a gentle curve from the thicker center to a thinner wheel tread. Making this profile by hand would require a lathe or some kind of turning device like a power drill.

    My first instinct is to use a craft cutter like a Cricut or Silhouette machine. Getting a perfectly centered axle hole by hand seems pretty difficult. Even if you keep the Kato wheel center (which solves the axle hole problem), cutting all the oblong holes by hand and all getting eight drivers to match seems very time consuming.
     
    gmorider and Mark St Clair like this.
  3. Mark St Clair

    Mark St Clair TrainBoard Member

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    Interesting ideas. My original intention is to use the existing driver as a base. Solves many of the problems you mention. Good news is only a single driver pair were replaced on the prototype. The other three pairs used spokes until the end of service.

    Thanks,


    Sent from my iPhone using Tapatalk
     
  4. acptulsa

    acptulsa TrainBoard Member

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    And you don't have to worry if the 3D print material is stout enough to take the torque, or hard enough to take the friction against the rail, if you use the rim you have.

    I figured your prototype had discs only on the main drivers, when you only asked about one design, and that with a heavy counterbalance. That was common in the mixed power era, and an excellent detail to model. Hope you can make it work well.
     
    Mark St Clair likes this.
  5. RailMix

    RailMix TrainBoard Member

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    If you know anyone with a benchtop CNC mill, that would probably be the best way to go. Establish the center, orient the crankpin properly and mill a shallow rcess in the spokes and counterweight to accept an insert made by 3D printing or machine cutting. Milling the spokes could probably be done on a manual mill using a magnifier and great care, but wouldn't be much fun. The gentle curve in the driver face. mentioned by Mr. Trainiac would be negligible in N scale, so might not be readily visible, let alone worth addressing.
    The other approach might be to 3D print a driver center and then clean up the I.D. and O.D. on a lathe for concentricity. This could be done using a 3D printed holding fixture. The real challenge presented here would be pressing the tire on and getting the alignment right.
    I know I'm talking about tools that most don't have, but maybe you know someone who does. Offhand, I can't think think of any simpler ways that would produce a good result.
     
    Mark St Clair likes this.
  6. Mark St Clair

    Mark St Clair TrainBoard Member

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    Tom,

    Thanks for the reply. From you and the other folks I am beginning to get an idea how to move forward. I do have a few tools, but all manual. I need to test out a few things. First up is creating a Corel drawing of the design. I have a few driver pairs form old locos in the "spares" box to experiment with. Updates and more questions are likely.

    Stay safe,
     
    RailMix and SLSF Freak like this.
  7. RailMix

    RailMix TrainBoard Member

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    The size of your spares pile was one thing that did cross my mind as there are bound to be a few missteps. Another question, since I have zero experience with Corel Draw: What level of precision is it capable of and is there any 3D capability? Also, can you export a 3D printing format such as .STL? That may determine the process you want to use(Cricut or 3D print).
     
    Last edited: Jul 29, 2021 at 3:39 PM

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