What’s the max depth of cut I can take when using a face mill?

The max depth of cut depends on the tool, material, and speed. With high speed facing, refrain from cutting deeper than 0.050”-0.075”. With heavy duty face milling cutters, you can go much deeper at certain angles: for 45 degree and 90 degree cutting angles, you can eliminate up to 0.25” at a time. However, this also varies based on the material you are cutting. If you are concerned about how deep you can face with a given tool and metal, it is better to air on the side of caution, but feel free to look up the specific specs for that part. See here.