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Thread: Insulator Substitute

  1. #1
    Join Date
    Dec 2002
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    594

    Post Insulator Substitute

    I'm working on a low tension ignition magneto (American Bosch). I need to replace the output lead insulator (it is missing). The info I have in a 1919 engine operating guide says the insulator is made from "soapstone". I don't know what the modern equivalent of this would be. I am thinking of using Delrin (Acetal) to make the replacement. Any input would be appreciated.

    Frank

  2. #2

    Post

    Don't know if it's the same soapstone welders use to mark steel. Similar to chalk, but much harder. I think ceramic would be a good visual substitute for an insulator.

  3. #3
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    Post

    Soapstone is what's used in marking pens for welding. You can get it anywhere welding supplies are sold (Even Northern). The stuff I have is about 1/4" x 1/2" rectangular and 1/4" round.

    Delrin may not hold up to the heat. How big of piece do you need? I have some small pieces of Bakelite-like material that's machinable. I used it to make insulators for a 1919 Ford magneto.

  4. #4
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    Dec 2002
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    Post

    I don't think the soapstone referred to in the book is the type for marking. This would have to be a type of bearing material as well as an insulator. There is a small contact that turns inside the insulator as the same rate as the armature to make the connection with the output lead stud.

    I don't think heat would be a factor in this case. This magneto is driven by the open cam gear through a skew gear. Everything is in the open.

    The insulator would have to be resistant to humidity, as not to swell the bearing area or break the housing.

    I do have some bakelite type pieces. Thanks for the offer.

    Frank


    [This message has been edited by PolskiFran (edited 05-27-2005).]

  5. #5
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    Post

    My Fairbanks R type mag uses bakelite for the leadout tower which holdes the carbon contact.If I remember right a lot of distributor caps are bakelite type plastic to this day.
    I just need one more tool,just one!

  6. #6
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    Dec 2002
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    Post

    I've already cut the carbon coil contact from an old distributor cap for the pickup. The cap material itself isn't thick enough. The whole insulator looks like a shouldered bushing about 3/4" long with the output stud coming from the bore on the shouldered side.

    Frank

  7. #7
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    Post

    Kind of like this Ford Timmer?


  8. #8
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    Post

    It quite possibly is soapstone. It would have some lubricity, and be an insulator. They also used mica in a lot of places for insulation for the same reason. Mica is available from some of the engine parts guys.

    If you are looking for a functional replacement, delrin is probably as good as anything. It will absorb some moisture, but not as much as nylon.
    Jim H.

  9. #9
    Join Date
    Mar 2004
    Posts
    135

    Post

    Why not try phenolic resin?

    Garolite / Micarta NEMA G-10 (fiberglass reinforced epoxy resin, FR4 for flame retardant version)
    Color: Opaque Green or Brown-Green Machining: Easy (Nasty and Quickly Wears Conventional Tooling)
    Maximum Temperature: 284°F (Does not melt, but will darken and eventually char at higher temperatures.)
    Dielectric (Insulator) Strength: Excellent - 800 V/mil
    Tensile Strength: Outstanding - 45,000 / 38,000 psi Flexural Strength: Outstanding - 75,000 / 65,000 psi
    Impact Resistance (Izod Notch): Excellent - 14 / 12 ft-lb/in
    Cost: 1" - $12, 2" - $46 (1.5"- $25)

    Garolite / Micarta NEMA G-11 (fiberglass reinforced epoxy resin, FR5 for flame retardant version)
    Color: Opaque Green Machining: Easy (Nasty and Quickly Wears Conventional Tooling)
    Maximum Temperature: 350°F (Does not melt, but will darken and eventually char at higher temperatures.)
    Dielectric (Insulator) Strength: Excellent - 900 V/mil
    Tensile Strength: Outstanding - 43,000 / 37,000 psi Flexural Strength: Outstanding - 80,000 / 70,000 psi
    Impact Resistance (Izod Notch): Excellent - 12 / 9 ft-lb/in
    Cost: 1" - $22, 2" - $89 (1.5"- $46)

    Garolite / Micarta NEMA XX (paper reinforced phenolic resin)
    Color: Opaque Tan or Copper Machining: Easy
    Maximum Temperature: 284°F (Does not melt, but will darken and eventually char at higher temperatures.)
    Dielectric (Insulator) Strength: Excellent - 750 V/mil
    Tensile Strength: Excellent - 15,000 / 12,000 psi Flexural Strength: Good - 16,000 / 13,200 psi
    Impact Resistance (Izod Notch): Fair - 0.65 / 0.6 ft-lb/in
    Cost: 1" - $7, 2" - $27 (1.5" - $13)

    Garolite / Micarta NEMA CE (cotton canvas reinforced phenolic resin)
    Color: Opaque Tan to Brown Machining: Easy
    Maximum Temperature: 239°F [257°F] (Does not melt, but will darken and eventually char at higher temperatures.)
    Dielectric (Insulator) Strength: Excellent - 550 V/mil
    Tensile Strength: Excellent - 11,000 / 9,000 psi Flexural Strength: Good - 17,500 / 15,000 psi
    Impact Resistance (Izod Notch): Good - 1.7 / 1.5 ft-lb/in
    Cost: 1" - $7, 2" - $25 (1.5" $13)
    Note: Machined parts are tougher than Garolite LE due to the heavier reinforcement fabric, but does not machine as nicely.

  10. #10
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    Jan 2004
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    Post

    Frank,

    You could use a pourable 2 part epoxy if a mold could be made. Epoxies have excellent moisture resistance and are widely used in the electrical insulation industry. Use a clear non pigmented version as they have better electrical properties than pigmented ones.

    Chris

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