The key to successful PCB engraving is consistent depth of cut. The cutter needs to go deep enough to remove the copper, but no deeper than that. If the cutter goes too deep, the cut becomes too wide (and the copper traces become too narrow, or even disappear completely).
Problem is, even a 3-inch board will have enough height variations to completely mess up the engraving. No matter how much you try to level the table or flatten the board, it will never be flat enough.
Commercial PCB prototyping machines use "depth rings" to keep the cutter at a constant depth. Hobbyists like us use surface probing. A program such as Autoleveller probes the PCB surface and adjusts the G-code for any height variations.
Once you figure out how to make consistent cuts, adjust the bit diameter in your CAM program to match the actual cut width. A "0.1mm" V-cutter will probably cut about 0.12-0.13mm.
Here is my recent work. I have yet to figure out how to spread the solder mask perfectly.