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17997RE: Magnetic chuck plans posted to files

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  • kwolson2002
    Mar 3, 2014
      Poker -

      Yes, I am doubtful that today's common magnet wire is up to having hot babbitt poured over it.

      I imagine the intent for the babbitt was two-fold:
      1) prevent the coil windings rubbing off the enamel due to energizing/de-energizing cycles, eventually short-circuiting the coil, and ending up in deep mischief
      2) provide a conduction path to help remove waste heat

      I am just a hack mechanical engineer from the northwoods, so I may be all wet on those suppositions.  If anyone has other thoughts, I'm all ears.

      I think small transformer windings are still dunked in varnish, aren't they?  That might be a cheap way to deal with the first, but not the second, consideration.

      The second criterion needs something which conducts heat well.  There are several low temperature alloys ("Cerro Bend" is a typical brand name), some of which melt well below the boiling point of water, others at quite a bit higher temperatures.  One or another might be well-suited on other accounts, but these alloys aren't cheap, so that dog won't likely hunt.  When used for their intended purposes (filling thin-walled tubing prior to bending to prevent wall collapse, potting small parts for machining, etc.) the alloy is re-used indefinitely, and the cost is amortized.  But, nothing in my garage amortizes, anyway - though I do get a bit of surface rust on stuff from time to time (I know, oxidize-amortize, not such a good joke).

      There are special thermal epoxies available, used for bonding thermal probes to surfaces, but again, they aren't inexpensive.

      What about the "Lab Metal" and similar metal-filled epoxy products?  Ever had any experience with those as a heat sink?  I wonder if JBWeld mixed with powdered aluminum (the stuff used to make metalic paint), would do the trick?  Vacuum de-gassing and/or vibration to remove air bubbles, perhaps?  Or metal-filled silicone?  Tub caulk is pretty cheap from big box stores...

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