I've have been successfully engraving steel at 4,500 rpm. At 3/4" per minute with a 0.2mm tip carbide engraving cutter. If you want to do it faster you need more rpm's. Double the rpm double the feed etc. Variable speed upto 25 to 30,000 rpm sounds like a good start.
Originally Posted by jaru-eri
I´m planning to buy a cnc mill and need to know which spindle speed I need for engraving in knife blades, mammoth and other bones and also leathers.