Fixturing Metal

Someone asked how I hold odd-shaped objects for machining. If you're Grant Stace, you build elaborate jigs with the intent to produce dozens of parts. The time and expense of producing such jigs is rewarded by the speed, precision and ease of changing out parts for machining. I'm lazy and only make 2 or 3 parts of anything, so I look for the easy way out.

I had to machine the reservoir end of the Girandoni receivers as I had done on the Lukens and Kuntz rifles before. Fixturing metal is a low melting point alloy which comes in various compositions, expansions and ductility depending on application. I use one type in dentistry to make durable models of the dentition in fabricating partial dentures. One must repeatedly place and remove a Chrome-Cobalt alloy casting on the model, which would soon wear and distort a stone model.

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The raw receiver casting is stabilized in an aluminum can with a modified R8 fixture to orient the axis of the soon-to-be-threaded boss. The molten alloy is poured in the can, immobilizing the casting.

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The casting and can are placed in a 4-jaw chuck, indicated in, center drilled and secured with a live center before turning the boss and shoulder.

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The turned and threaded receiver end.

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The unfinished reservoir is screwed on the receiver to check fit and orientation.

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The receiver removed from the metal in a pot of boiling water. Use gloves and/or pliers!

Pretty straightforward? The downsides are cost of the metal, embedding/removing the part and positioning each part accurately. It's practical for short runs and one-offs.

Martin



'It used to be only death and taxes; now, of course, there's shipping and handling, too.'