Re: [TCML] Spark gap assembly, acrylic?? and toroid size

[Quarkster <quarkster@xxxxxxx>]

Phillip -
   
  With all this talk about the machinability and dimensional stability of "polyethylene", remember that there at least three different types of PE (low density, medium density, and high density, also known as ultra high molecular weight, or UHMW PE) that have quite different mechanical properties. Low-density PE (cutting board material) is extremely soft and waxy, can be easily gouged with a fingernail and has a very low heat-deflection temperature. As you move up to medium and high density materials, the mechanical properties improve somewhat, but the material is really not rigid enough for any mechanical application where anything other than small loads are applied. It's fine for MMC baseplates and lightly-loaded brackets, etc but for anything requiring structural strength or dimensional stability materials like Delrin, LE grade phenolic, or the G-series of fiberglass-epoxy composites are much better choices.
   
  Regards,
  Herr Zapp
   
   
  Phillip Slawinski <pslawinski@xxxxxxxxx> wrote:
  I guess I was just wondering because nearly my entire base is made from PE.
I had several of the parts machined in a shop. Some of the holes are
threaded, and they work fine provided you don't over torque them.

On Wed, Jul 16, 2008 at 9:07 AM, Lau, Gary wrote:

> I guess I wrote from a machinist's perspective. Very soft plastics like
> polyethylene cannot easily be machined to a high tolerance in the same manor
> as say Lexan or Delrin. It's not to say that it cannot be cut or drilled,
> just that it won't come out as nice. Tapping is also likely to be a
> problem.
>
> Regards, Gary Lau
> MA, USA
>
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