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  • Electrical insulating material question?

    I am in process of getting things rounded up so hopefully I can start restoring my Fairbanks engine this winter.

    My plan of attack is to tackle the magneto first.Upon disassembly I have noticed that part of the lead out tower had dropped down and when I removed the shaft it broke off one side of the insulating ring.Its kind of a tapered washer affair,either pressed or glued to the shaft and appears to be bak-a-lite.My plan is to turn out a new insulator,but I am wondering if I have to use bak-a-lite or can I substitue for something like teflon.The voltage is 1,000+ as it is a high tension mag.
    I just need one more tool,just one!

  • #2
    Teflon would work fine. A much better insulator than bakelite.

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    • #3
      Weird,

      Most, not all, plastics are good insulators. The insulating properties are degraded by adding pigments or fillers to the resin, so "clear" unfilled, unpigmented resins have the best electrical properties( black is one of the worst colors). If the resin has to hold something and be rigid that may determine what type to use. If all it has to do is insulate most plastics will work, although a thermoset plastic would be preferred (e.g. epoxy, phenolic, or polyester) because they don't melt. Teflon would also work ($$$$).

      Chris

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      • #4
        Pretty much any plastic would work, true, but try to pick one that doesn't get brittle, or soften with heat. Teflon, nylon, delrin, there's phenolic, - you could use hdpe, lexan, acrylics, but these will soften at lower temps. Another way is make a blob from epoxy and machine that.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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        • #5
          I don't know what size your in the need of, but a friend had a ball of teflon, almost the size of a bowling ball. He put it on ebay, with no bidders. If you need some, I will ask him what he wants for it. (It is in my pocession anyway, I just don't own it)
          Just a thought, since that stuff seems to be high priced.
          If you already have some, just tell me and I won't bother asking.
          David from jax
          A serious accident is one that money can't fix.

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          • #6
            7 and 3/4"... says 20 pounds written in ink on it from when he had it on ebay.
            David from jax
            A serious accident is one that money can't fix.

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            • #7
              It's probably closer to 15,000+ volts. What ever you do, DON'T use the windshield urethane stuf to try and mold one. I tried to use that and sparks were flying everwhere. It must have lots of carbon black in it.

              Which plastic to use will depend on expected temperatures. A piece of urethane body mount (auto/truck) could be machined. Depending on the size, I have a piece of phenolic block you can have. I can cut off about one cubic inch. (I need a little to fix a model T flywheel mag.)

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              • #8
                Just thought of something else... Would the cutoff top of an ignition coil work? I have a few old coils around here somewhere.

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                • #9
                  Just to clarify, Bakelite and phenolic are the same basic material. Bakelite is almost always sawdust or mineral filled, but phenolic sometimes is filled with fabric, paper, or cotton.

                  Phenolic machines ok with sharp tools, but can be abrasive. It's easy to get and has good electrical properties, so you might as well use it.

                  The dielectric strength of phenolic is 5 to 10 times higher than nylon, for example, depending on fillers etc, and will tolerate higher temperatures.

                  Ken has a good idea-distributor caps, rotor buttons, and coils are all made with phenolic.

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                  • #10
                    Phenolic has 5-10 times the dielectric strength of nylon- is that true? I'm amazed that a material which has various fillers in it would be that good compared to nylon. Come to think of it, distrubuter caps do have a habit of arcing through after a while. Hmm, planned lifetime limit? Bakelite, phenolic, and high voltages-hmm - use teflon and be done with it.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                    • #11
                      Thanks to all for the replys,yes David I do have some Teflon,but much appreciate the offer.

                      I also stumbled across a piece of micartia board,kind of leaning towards that,it will be stronger than the original and should take the heat better right?
                      I just need one more tool,just one!

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                      • #12
                        I have a piece of micarta about 6 or 7 inches thick, and 17" in diameter. After I left the shop's employ I was over visiting and noticed a job cutting the same stuff, having a drop just like mine. I went in and told the boss congradulations on that new job. He said it was just a favor to another shop, they didn't have a big enough machine to cut it. I asked him if he knew what the job was used for, (he didn't)
                        It was for a customer he had and the other shop was trying to get their work, out from under him. I recognised it because I worked for that customer for 15 years. Pretty bad when you do one of your customers work for your competitor...
                        I think they came and picked up the job, uncompleted. We got a call to do the same job a couple weeks later. It is one of those types that only gets done every 10 years or so, so they must not have been able to complete it.
                        David from jax

                        ------------------
                        Have gun, will travel.
                        A serious accident is one that money can't fix.

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                        • #13
                          I did a little more searching, and found this:

                          http://www.boedeker.com/mtable.htm
                          which is a table of materials where you can sort by your chosen property. Depending on grade it looks like some nylons can come close to or do better than some phenolics. Teflon is surprisingly low compared to the others.

                          (This isn't the source I had based my earlier posting on)

                          But, scavenging material from a high-voltage part like a distributor cap or coil ought to get a suitable material without having to dig through reams of data sheets...

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                          • #14
                            There's really no need to dick around with material data sheets if you use the right stuff for the job - Bakelite worked well 'way back when and it works well now. Its mechanical and electrical properties are both very good for this sort of application. Its original development was for molded parts, but it can be cut and machined just fine. It's never clear or in bright colors - always one shade or another of brown.

                            Bakelite was a trade name for Leo Baekeland's original commercial version, circa 1907. Look for it now in rod or plate form at plastic suppliers - it will most likely be listed as "phenol formaldehyde" or "phenolic."

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                            • #15
                              Thermo Plastics, like Bakelite do not absorb moisture like regular plastics..
                              Yes, Teflon (and others) absorb water..(swell in the presence of steam i.e.)
                              this changes the dialectic ratings .

                              Mc Master Carr has bakelite rounds etc.

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