Ok... I have a spring loaded drag engraver I use occasionally for misc jobs. I originally used diamond tipped stylus in it, but the diamond tip would snap off on some pretty insignificant irregularities. When I needed to do some stuff once, and did not have a good diamond tip on hand I chucked a broken carbide end mill in the lathe and used a fiber wheel to grind/polish it to a nice point. It worked well enough for the application on brass. I have since used it on aluminum, brass, and steel (tests on the side of a socket). With some steels it take 3 or 4 passes to make a nice image, but it works. What do the diamond tip drag styluses do that this one doesn't?
Well, on some materials (like brass) the carbide one does leave a rough feel if you run your hand over it.