Checking Internal Threads

What's a good material for molding internal threads which can be unscrewed so the pitch diameter can be checked with thread measuring
wires which will work on both metal and plastic?
I'm thinking a fusible alloy (bizmuth, etc) and know it will work on the zinc die cast parts to be checked but no so sure about the glass filled nylon parts.
I'm working on a set of unscrewing cores for a used mold which was made somewhere else and have no history on the tool so I'm to work steel safe and tweak it in a later date. I'd much prefer to work to numbers I can measure than the wild ass guesses the halfwit (OK, they're not really halfwits, they're just stoned half the time) moldmakers on the job expect me to make based on how the parts fit on a socket head cap screw. Feh.
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Black Dragon

I met a young man in Chungking
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Black Dragon wrote:

Cerralow 136
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John R. Carroll



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John R. Carroll wrote:

Well I'll be damned.
CERROLOW 117
http://hitechalloys.com/hitechalloys_002.htm
Heck, that stuff will melt if left out in the shop in July. Much of the glass filled nylon we mold lives in engine compartments. I think we have a winner. :)
Thanks John.
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Black Dragon

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John R. Carroll wrote:

What's a good release agent?
I'm thinking PAM (spray cooking oil) ought to do the trick.
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Black Dragon

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Black Dragon wrote:

I don't think it wil be, but maybe. Use mineral oil, which is recomended. That's what is used to form musical instruments using this approach and it worked for me.
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John R. Carroll wrote:

And preheat your part to about 20 degrees above the eutectic temp of the casting alloy.
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John R. Carroll



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John R. Carroll wrote:

Mineral oil.
Got it.
This only proves once again this newsgroup isn't dead. Saved me an hour of web searching trying to wade through of plethora of different opinions from webspurts (like Cliff) who may or may not know what they're talking about.
Is hard to beat information from a trusted source. :)
Thanks again.
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Black Dragon

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