"Back on Face" Problems

[Cold Spring]

Several friends asked for more info on my technique. Here's a photo collage showing work on a 16 gauge Fox. Same technique would apply to an Ithaca Flues, subject of this thread, except that the end mill would be sized same as the Flues hinge pin.

Just as an aside, I'll add that I started doing this work on my own guns because of sloppy workmanship, multiple times, by gunsmith XYZ who does rejointing work. I worked part time as a machinist while in high school and college, and nowadays have access to a large machine shop owned by two friends. Sorry, I won't badmouth this gunsmith on the world wide web. Please don't ask for his name. Maybe he does better work for others? Last comment, there's no reason why most any gunsmith who owns a vertical mill can't do similar high precision work.

After TIG welding


Milling machine adjusted for +.005" on the X (long axis). In this case it was .0035" for "off face" measurement + .0015" for final fitting


New radius milled in the hook using an end mill sized for a 16 gauge Fox hinge pin


New radius is cut and is ready for fitting. Note how little "heat" propagated to the barrel hook


Fitting about 1/2 way complete using oil lamp soot


I like to use Dykem (machinist layout blue) for final fitting. Dykem is much thinner than soot. Almost done here but I'll add that most factory done work will show even less contact than in this pic..

[Double Play]

Frank,
Thanks for sharing your procedures in pictures. I’ve made a couple of new roll joints/guide rolls for both hammer and hammerless guns and by adding the needed material was able to achieved the same result with no file fitting. I would be very interested in getting more details on the fixture you used to hold the barrels while machining in case I decide to try the welded hook method. Thanks, Larry

[Twice Shooter]

Yes, please show the fixture. Thanks, Tom

[Eldon Goddard]

I did not have that much contact on the hook but I did have a good amount in the center of the hook. Are not most hinge pins tapered? How do you account for that when milling as end mills are not tapered? I agree that using a vertical end mill would be the best choice and I do have some experience machining. I have access to a vertical mill and even a cnc mill but since it is at my school bringing in a set of barrels is out of the question. I may be able to get the permission, but I doubt it.