# machineable non electrical conducting materials



## caseyvand (Sep 27, 2014)

Hi.....Are there tougher or harder machineable materials that do not conduct electricity other than delrin? I need to machine a non conducting collar with a brass electrical contact  in it. At present I'm using delrin for the collar  but I end up with a thin layer of delrin on the electrical brass contact and loose a good electrical contact. This is a ignition contact for a model hit and miss engine. The other contact is spring loaded and is constantly rubbing on the collar and there is some minor arcing that may be part of my problem
Thanks ....Casey


----------



## John Hasler (Sep 27, 2014)

Bakelite (phenolic composite) is the classic for that application.


----------



## JimDawson (Sep 27, 2014)

Micarta® Industrial Laminates might be a good choice for that application.  Very good electrical properties as well as high heat performance up to 250F.  There are several different compositions available.


----------



## hman (Sep 28, 2014)

I've specified a material called FR-4 for such purposes when I was designing machinery at HP.  It's basically epoxy fiberglass.  Quite tough, due to the fiberglass content, but I'm sure it will do a GREAT job dulling tools ... and be sure to wear a dust mask!

https://en.wikipedia.org/wiki/FR-4


----------



## Alan Douglas (Sep 28, 2014)

If the rubbing contact arcs when it breaks, that will attack any organic insulating material.  I suspect you'll have to use a cam to break a separate contact, and not try to combine the functions.

Teflon might possibly stand up.


----------



## Tony Wells (Sep 28, 2014)

If your pockets are deep, have a look at 40% glass filled PEEK. 

But agreeing with Alan, your design will undoubtedly live longer if you mechanically lift or break the contact away from the actual metal/insulator junction. Be careful if you go with something like Ryton. Probably with most of those materials, you should go with whatever the "natural" color is. The colorant is often conductive to some degree an can cause some strange problems.


----------



## DMS (Sep 28, 2014)

If it is going to take some heat, PEEK seems like a good solution. If it is not going to run hot, UHMW is very resistant to abrasion, though, it's a bit tricky to machine, and is a bit soft.


----------



## jgedde (Sep 28, 2014)

I can think of a few good choices depending on what you can easily get:

FR-4 (which is what PC boards are made from.  It's flame retardant), G10 fiberglass, G11 fiberglass, bakelite, phenolic, delrin, Teflon, UHMW plastic, Corian, etc.  

Is there a contact that has to rub on this collar and periodically make contact with the brass?  If that's the case, FR4, G10, G11 and glass filled PEEK are out.  They will wear out your contact.  In that case, phenolic is an excellent choice, with bakelite a close second.

John


----------



## Tony Wells (Sep 28, 2014)

Is there a capacitor across these ignition points?


----------



## John Hasler (Sep 28, 2014)

Bakelite is phenolic.


----------



## pineyfolks (Sep 29, 2014)

Ryertex may work but it's dusty to machine.


----------



## OldMachinist (Sep 29, 2014)

I use Garolite G-11 from McMaster Carr for insulating material. 
http://www.mcmaster.com/#garolite-plastic/=txm7jb

I know it says to use diamond tooling to machine but they are talking about in production. Carbide turning tools and high speed drills work just fine for making low quantities. Cover the lathe ways and wear a dust mask.


----------



## jgedde (Sep 30, 2014)

My understanding was that phenolic is bakelite with embedded cloth weave.  Then again, I've seen phenolic PC boards that had no obvious fabric...  So, if phenolic and bakelite are the same (which could very well be), what's that stuff called that has the cloth (not fiberglass) in it?  BTW, I haven't seen that stuff used in years.  

In any case, when I recommended phenolic, that's the stuff I meant.

John


----------



## Ebel440 (Sep 30, 2014)

There are also machinability ceramics available. We made some parts out of one type but can't remember the type. I believe it came from msc. machined it  with carbide tools


----------



## JimDawson (Sep 30, 2014)

John, I think you are referring to Micarta.  It is a phenolic with a cloth, paper, or glass filler depending on the grade.  I have a few pieces of that kicking around out in the shop.  Some with glass, and some with cloth.  You find the stuff in some of the older electrical switch gear.


----------



## John Hasler (Sep 30, 2014)

Bakelite is a trademark for phenolic-based thermosetting plastics.  It's been made with all sorts of reinforcing materials.  All the patents have long since expired, so of course there are lots of similar products with their own trademarks.  I call them all bakelite.  They're all the same stuff: some sort of fiber impregnated with phenolic resin and cured under heat and pressure.   Of course, you must consider the composition of the particular variety you choose for a particular application.


----------



## OldMachinist (Sep 30, 2014)

Phenolic comes in many grades depending on the base material.
"C" canvas
"CE" canvas electrical grade
"L" linen
"LE" linen electrical grade
"X","XX" and "XXX" paper(the more x's the better electrical properties, lesser x's higher strength)
"G3" fiberglass


----------



## Alan Douglas (Oct 1, 2014)

And the molding grades would use fillers like wood flour, ground mica, asbestos, and probably other things.


----------



## kd1yt (Oct 1, 2014)

I don't know if you can get it in the right size and shape for your application, but cross-linked polyethylene ("PEX" like is used in plumbing) is astonishingly robust and resilient stuff.


----------



## jgedde (Oct 2, 2014)

JimDawson said:


> John, I think you are referring to Micarta.  It is a phenolic with a cloth, paper, or glass filler depending on the grade.  I have a few pieces of that kicking around out in the shop.  Some with glass, and some with cloth.  You find the stuff in some of the older electrical switch gear.



Thanks Jim!  Micarta rings a bell!  That's the stuff.

Problem is my "20-20 memory."  Within the last 20 minutes or more than 20 years ago, I remember. :rofl:

John


----------

