I have no idea what kind of steel P38s are made from, so machining and welding are going to be guesswork. I had the raw forging and the original frame piece XRF tested to see if I could narrow down the alloy used, and the results were fairly inconclusive. The manganese content was in the range of 4130, spark testing looked similar to the 4140 I compared it to and when I heated and quenched a chunk, it got hard-ish so it's got some carbon in it. For lack of better options, I decided to treat it like 4130 for machining and welding.
I hate machining steel. There is nothing I like about it. It's not very forgiving if you do a dumb, it's hard on tooling, and worst of all, unlike aluminum the danger glitter is more than happy to stab itself into your fingers like tiny little needles. Machining from a raw forging like this presents it's own challenge too because I know there is a lot of extra material there, but I don't know where. After whacking off the chunk of forging that I needed, I decked the top and cut the overall width so I would have some straight, square surfaces to work with. I decided to start my CNC work with the inside of the trigger guard because its the area with the least amount of extra material on it. I tried to centerfind the pocket with the proper tools....and promptly broke a cutter on the first pass because it was too far off. So I eyeballed it instead and didn't break the next one. Since the trigger guard is a weird shape, I also decided to drill the trigger pin hole to use as my program center so that I had an easy to find reference point.
Slow and steady is how my little mill mills, and with mildly hard steel it's even slower. My feed rate was pretty average for the material, but my depth of cuts were very shallow. A whole day of machining got me this far:
After a whole lot more painfully slow machining the first side was done.
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