Break-top Revolver hinge

[earlgo]

A buddy and I were discussing a machining problem at lunch and neither of us knew the answer. Attached is a picture of a Break-top Revolver frame. We do not know how the hinge recess was machined in commercial production. The 'back' of the recess is the same radius as the side bosses. There seems to be no obvious tool that can make this cut. Any thoughts on this?

His problem is for the throne of a mariner's astrolabe, but the machining issue is the same.
--earlgo

[Russ Hanscom]

Pretty sure I have seen the tooling for that - I will dig around and see if I can find a picture.

[Glenn Brooks]

Earlgo,

Are you describing the inside radius of the slot? If so, I would think an appropriate width and radiused shell mill cutter on a horizontal mill would slot the hinge out and leave the proper radius -tooling similar to that used to mill teeth into a gear blank, only with a square face and perhaps sharpened on both the sides for end and side milling.

Glenn

[earlgo]

Glenn:
The inside radius of the 'back face' is exactly the radius of the side bosses. Which is to say the center of the back face radius is coincident with the center of the radii of the side bosses. Agreed one could use a milling cutter to get 90% of the metal out, but the final radius is the trouble spot. Therein lies the issue.
--earlgo

[John Hasler]

I think I can see how to make a sort of a special-purpose shaper or broach-like tool to do that.

[SteveHGraham]

Is there such a thing as rotary shaping? That would work, to finish up after an end mill. Turn the part past the cutting edge instead of dragging a cutter over the work.

If I were trying to do this in a home shop under threat of death if I failed, I would mount this thing vertically on a rotary table and make some kind of one-off tool with a straight edge. Raise the table after each set of cuts.

[SteveHGraham]

From the web:

"Contour shaper Contour shapers are standard shapers fitted with an additional trace mechanism. In this shaper a template and a follower are used to produce a contour similar to the shape of the template. It is suitable for producing shapes that cannot be produced by other shapers."

[Lew Hartswick]

After googling " throne of a mariner's astrolabe" I don't see any place where that sort of joint is needed.
I am wondering if the revolver joint is "built-up". A friend of 30+ years ago had a revolver like that but I wasn't into machining then so it never would have occurred to me to wonder or look at it.
...lew...

[NP317]

Lost-wax casting.
~RN

[Russ Hanscom]

EDM would also work but I doubt it was available back then. Forging could be an option. There is an old machine accessory for making that pocket, think I found a picture before under cigarette making machinery. Several small idler gears driving a tiny mill which is about the size of a single knurl.

[earlgo]

Investment cast? Probably not. According to Roy Jinks in the History of Smith and Wesson, the patent of July 10, 1860 was held by Abraham Gibson, patented the feature whereby the cylinder and barrel together are swing away from the recoil shield. In 1869, after S&W bought out all the patent holders of similar patents, the Charles King patent model of the S&W Model 3 break-top revolver was issued in August 1869.
This got me thinking and I pulled out the 1960's H&R Sportsman. It sure looks like the recess was investment cast.

But this was made in 1960, not 1870.

Forging? Most likely used to get the rough shape, but not the finished knuckle. The small milling cutter driven by gears is probably the correct answer, but that is yet to be proven.

S&W, Iver Johnson, Harrington and Richards, and a 'few' other makers of break-top revolvers used this hinge.

Thanks for the responses fellows, and if the answer is found, there will be an update.

--earlgo

[stephenc]

I think everyone is to busy thinking machine tools and getting off track .
I would lay my money on a hand tool of some sort utilizing the hinge pin holes after reaming to finish the casting .

1870'S ... machine tools are expensive . Labor is cheap