Looking forward to seeing the results of a machine Sidmind, you could do a far more intricate etch with a machine than you could with my approach!

Rick- You're right about work surfaces and keeping the piece still, that was one of the reasons I posted the above method. It's a bit crude as you can see but it works on hollow grinds just as well. I suppose it all depends on what you want to etch and what your drawing skills are like. Mine are fairly limited so I tend to keep it simple!