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.

[IMG][/IMG]
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.

[IMG][/IMG]
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.

[IMG][/IMG]
The turned and threaded receiver end.

[IMG][/IMG]
The unfinished reservoir is screwed on the receiver to check fit and orientation.

[IMG][/IMG]
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.'

I find the Fixturing metal? Are the vapor fumes harmful? I would like to see update on the gun you were working on. Thanks, Chris

Greetings Chris,


Here's some info:

http://web.archive.org/web/20050320215953/http://www.harpellassociates.com/a/a-fusible.htm

At the temps we use them, I don't think vapors are a problem. Search the web for fusible alloys and look at the MSDS sheets.

I've purchased it from MSC Industrial and eBay.


Later, Martin

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

Thanks Martin, Thats one idea I'll use! I have a few pounds of chambercast I'll be trying.
Mike

I got a new shadow. I had to get rid of the other one -- it wasn't doing
what I was doing.

Though my uses arent so ambitious and grand as yours nowadays, I've been using and re-using the same big ingot of "cerro-safe" for about 30 ears now.

Great for backing up real thin parts, and can even be poured into wood cavities.


I once made a co2 charging adapter for an old Giffard using the valve threads as a mold ... seems dangerous, but it worked just fine for testing the gun.

Greetings LD,

Have you ever used Cerro-Bend for bending tubing? If so, did you discover any tricks or limitations?


Thanx, Martin

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

I have been ignorant of the product! I have used sand in tubes to support them while bending, having been told its a good way, but my results with it were mixed.

I havent even tried cerrosafe in bending tubes, as I perhaps felt it was too hard, I dunno.

I HAVE found cerrosafe useful in helping to prevent/reduce burrs inside a tube on breakthru when drilling.

...is this company's product "MITEE-GRIP"

http://www.miteebite.com/

It's like wax paper you put between your part and fixture. You clamp the part, heat it, let it cool, then remove the clamp. It glues the part to the fixture for machining. When done, you heat it up again to remove the workpiece.

I've used it for milling thin aluminum parts where clamps couldn't be used. Even held a glass mirror onto the end of a faced bar to grind the OD to size once.