It’s the same thing all over. Got a hammer? Start looking for nails…
Hey! I’ve a CNC mill! What can I do with it? *shakes head in shame*.
Engraving. CNC. Cool.
CNC engraving requires (what a shock) research.
This involves having a high speed cutter remove material from a surface (speeds in the 10 000 RPM range and above; hello High Speed Spindle project!) Naturally, the feeds and speeds are dependent on tool geometry and material being worked. It can work on metal, wood, plastics, generally without worries. The tool bit can be held rigid, in a spring loaded holder (for uneven surfaces) or a nose collar.
Example Spring Loaded Holder and Engraving Bits
This involves use of a diamond or carbide tipped tool to be dragged across the surface to be marked. I understand it’s typically slower than a rotary method, but can have very good results on softer materials.
Similar tools are used, either Carbide or Diamond, and the tool is spun at a high rate of speed, simultaneously removing a surface layer of material and polishing the underlying. This is used to engrave glass, I’m told. Have to try it out!
Can be done on a variety of materials, and apparently has overtaken all other forms in engraving shops as a primary tool. However, it can generate noxious fumes from the material being worked, apparently has issues with certain colors and types of metals, cannot be done all surface treatments, and can require a stand along machine (unless you make a DIY laser attachment for your CNC mill, hmm).
WidgetWorks highly regarded Drag Engraver (they have both 1/4″ and 1/2″ shanks; 1/4″ linked)
The following links are straying a bit away from Mini-Mill CNC, but good for the high end. Here’s a ahem, low end example: Fun of DIY – Raspberry Pi DVD Laser