Jeff's Toy Box: I hate machining steel.

Now for the hardest part of my "doing it the hard way" Uzi project, the bolt. There are a lot of differences between semi-auto and full auto Uzi bolts, primarily because of the striker instead of the fixed firing pin. I could have bought a factory semi-auto bolt, or I could have modified my original bolt, but as previously discussed, I'm an idiot and apparently a glutton for punishment. I decided to just make my own.

I made a CAD model of my FA Uzi bolt, then added the necessary modifications for semi-auto use so that I could CNC machine it. The factory Uzi bolt is 4130 steel, but I decided to make mine out of A2 tool steel. I chose A2 because it machines alright, it's very tough without being too brittle, and most importantly, I have a large chunk of it.

I hate machining steel. Nothing about it is any fun. It's hard on cutters, it's painfully slow compared to aluminum, and the chips are tiny little razors just waiting to bury themselves in your skin. I'm also used to machining aluminum but very little steel(and even less hardened steel) so I run steel very conservatively. My little CNC mill is not fast, and it is not powerful, I could never run aluminum at the speeds I'm used to. But for steel, I don't need high speed anyway so it works out alright. I use carbide endmills for everything because life is too short for high speed steel, and even good carbide is cheap these days. Also machining high speed steel with high speed steel cutters is likely just going to chew up cutters so carbide is cheaper in the long run.

My new bolt is going to take 5 setups to machine, basically machine a side, turn it in the vice, machine the next side, and so on. I don't need to machine the top because it's already flat. After several hours of painfully slow machining, it's starting to look like something.

Operation 1, the right side: