How do I determine an acceptable depth of cut?

You should not exceed the maximum depth of cut for the device you are using. For square shaped inserts, do not exceed ⅔ of the cutting edge length. For other shaped inserts, the maximum depth of cut ranges from a quarter to a half of the length of the cutting edges. In general, you should decide on a consistent value for rough cut-s that is less than 0.100” and a smaller value for finishing cuts. Here is a useful resource for depth of cut for various lathe tools.