Last time I posted about the Uzi, I started machining the bolt. In what I'm sure will be a shocking surprise, in this post I'll finish it. I got all the sides machined last time, all that's left are the ends, and just like a loaf of bread, the ends are the worse parts.
This operation to finish the back side of the bolt is one of the most nerve wracking things I've done in a long time. All there is to it is a little bit of 3D machining, and drilling three holes. Why was so nerve wracking? Because the hole for the recoil spring is nearly 6" deep, through moderately hard steel, with a less than ideal coolant situation. After more painfully slow machining/drilling with very small pecks and full retractions between pecks, it was done. The Z axis got a workout that day, I tell you what.
With that done, there was only one operation left, but it was the most critical. The Uzi being what it is and working the way it does, it generally doesn't require much precision. This last operation is the only one that that really matters and it has to be exactly right. Trimming the front end of the bolt and machining the bolt face is what will set the headspace for the gun. Without having the headspace right, the cartridge case could rupture and the gun blow up. It's not quite as critical with a blowback as it is with a locked breech system, but still important. Finish drilling the recoil spring hole was no biggie but of all the painfully slow machining I've done, what's next was the slowest. I wanted to avoid chatter in the cartridge recess/bolt face as much as possible. To finish machine the bolt face, I had to use a 5/16" cutter hanging out of the collet 4", spinning at just a few hundred RPM, and stepping down a whole .010" at a time. Then I had to drill the hole for the firing pin tip, and my long collet only cleared the side of the bolt by .020". Know what's fun? None of that. But it worked and got the job done.
I actually did one last manual operation once the CNC work was done. I located and drilled the through hole for the extractor retainer pin on the mill by hand. It crosses the extractor hole off center and to drill it first might have made the extractor drill bit wander. All in all, I think it turned out alright. For something I reverse engineered with a calipers and machined in a tough material that I'm not very familiar with, I'm satisfied with the results. Here it is next to my original IMI bolt:
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