Ian
Notorious member
Just had an idea and I can type faster than write, 5 minutes to act on an idea or it's lost forever, yada yada.
The problem with lathe-boring a mould always comes down to tool flex and it being near impossible to make a really sharp point or rounded nose shape to the bullet. The other problem is working around the metal that must be left for the lube grooves. Even single-pointing a mould cavity with a 10:1 pantograph lathe tracing attachment still leaves one with the problem of tool flex because the boring bar must be TINY.
So what about grinding a spoon-type boring tool with TWO, opposing cutting edges to bore the cavity, then going back with a boring bar to cut negative grooves inside the mould, then making press-fit half-washers to install in the grooves, filing them flush with the mould? If it were done carefully, the holes in the middle of the washer wouldn't even need re-boring because everything would be made concentric in the first place. Two washers would be made for each lube groove due to metal loss splitting the washer. Holes could be drilled in each block from the top and pins installed as extra insurance to capture the half-washers. Draft would need to be accounted for when facing the washers. Gas check shanks could be made in similar fashion by counter-boring the top face of the mould for a pair of washer halves and staking them in place.
I know it sounds like a lot of trouble, but .30-caliber and smaller, pointed bullet cavities are tough to do on a manual lathe due to tool size. Just roughing the hole and finishing with a double-sided form tool plunged straight in like a drill and inside-boring washer grooves ought to be a lot easier than trying to single-point the thing, or use a single-edge form tool and a second form tool just to carry the bullet point out smaller.
Another idea for those who PC or tumble lube: A microband mould could be easily bored with two tools, one being a two-sided spoon bit used like a drill, but no larger than the minor diameter of the micro-grooves. A second form tool could be used just to bore the driving bands out and fade the front band into the nose all in one shot. Using two tools like that it would be much easier to make identical, multiple cavities on a manual machine because only the depth of each tool and the amount of diameter cut of the drive band tool need be precise/repeatable, and tool flex variances and breakage would be virtually eliminated.
The problem with lathe-boring a mould always comes down to tool flex and it being near impossible to make a really sharp point or rounded nose shape to the bullet. The other problem is working around the metal that must be left for the lube grooves. Even single-pointing a mould cavity with a 10:1 pantograph lathe tracing attachment still leaves one with the problem of tool flex because the boring bar must be TINY.
So what about grinding a spoon-type boring tool with TWO, opposing cutting edges to bore the cavity, then going back with a boring bar to cut negative grooves inside the mould, then making press-fit half-washers to install in the grooves, filing them flush with the mould? If it were done carefully, the holes in the middle of the washer wouldn't even need re-boring because everything would be made concentric in the first place. Two washers would be made for each lube groove due to metal loss splitting the washer. Holes could be drilled in each block from the top and pins installed as extra insurance to capture the half-washers. Draft would need to be accounted for when facing the washers. Gas check shanks could be made in similar fashion by counter-boring the top face of the mould for a pair of washer halves and staking them in place.
I know it sounds like a lot of trouble, but .30-caliber and smaller, pointed bullet cavities are tough to do on a manual lathe due to tool size. Just roughing the hole and finishing with a double-sided form tool plunged straight in like a drill and inside-boring washer grooves ought to be a lot easier than trying to single-point the thing, or use a single-edge form tool and a second form tool just to carry the bullet point out smaller.
Another idea for those who PC or tumble lube: A microband mould could be easily bored with two tools, one being a two-sided spoon bit used like a drill, but no larger than the minor diameter of the micro-grooves. A second form tool could be used just to bore the driving bands out and fade the front band into the nose all in one shot. Using two tools like that it would be much easier to make identical, multiple cavities on a manual machine because only the depth of each tool and the amount of diameter cut of the drive band tool need be precise/repeatable, and tool flex variances and breakage would be virtually eliminated.
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