My Grandpa was chief machinist for one of the Bay Area refineries. He’d have loved this….
Mike Sirois over at On Target Technologies seems to have made quite the name for himself with his custom barrels for the T/C Contender and Encore. They’re alleged to be extremely accurate — due no doubt in part to his EDM — Electrical Discharge Machining — method. You can watch it in action here.
EDM is an automated process that can run unattended. It utilizes electricity to disintegrate everything in the electrode’s path, imprinting the electrode’s profile into the parent material. The machining takes place on a molecular scale….
–from the OTT website, emphasis mine.
Gawd I love modern technology!
EDM isn’t very new. I made my own prototype machine when I was in high school in the early 70’s from a project outlined in (I think) Popular Science. I’m sure computers and such make it much more useful than what I had. I used the drill press to feed the electrode into the material being machined. My fascination was being able to make small square (well, almost–the corners were a little rounded) holes in very hard metal.
EDM is the process used by Mag-Na-Port since their start in the ’70s.
Though the basic technology isn’t new, seems to me that this company is the first to conquer the “deep, narrow hole” issues and thus, be able to translate it into a rifle-length barrel.
I’m thinking that damn little in the way of lapping or break-in would be indicated. But I can’t say for sure, as that link on their site wasn’t working.
Given that I do have the basis of a Mauser based custom now in hand, I’ll be taking a very close look here.
Thanks for the tip!
Jim
Sloop New Dawn
Galveston, TX
EDM in metals certainly rarely works at the molecular level. Solid (frozen) metal is generally crystals of atomic metal. Alloying elements may form molecules but they are usually rejected from the solution as it solidifies leaving them at crystal boundaries and usually weaken the whole.
EDM works by melting and vaporising a thin top layer of the surface of the metal. Being bathed in a fluid, most of the metal freezes in the liquid and is flushed away from the gap between the electrode and material. Some of the vapor re-freezes on the workpiece too leaving a rough surface.
EDM can be used to “polish” a surface too. When “polishing” the EDM is still is removing material but at a much, much slower rate. I doubt that you can get much better than a 32Ra finish economically with and EDM. There are electropolishing methods, not EDM, you could use after the shape was made.
EDM does have several advantages over other methods of rifling a barrel: Almost zero residual stress. No machineability compromise on barrel material. Complete and exact control of the twist rate. Easily make gain-twist barrels. Odd geometry rifling, including polygonal, would be a snap (think of the experimental rifling shapes you could try; buttress rifling; sinusoidal to reduce fouling, etc.).
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