I have been toying with the idea of making a CNC machine to engrave dies for making coins/medals and would be grateful to get some input from more experienced forum members on the overall design. Basically I am envisioning a system able to create very small feature size over an X-Y plane of less than 2"x2" with a Z-axis distance (depth) of less than 1/4". The main question I have is that given the limited range requirements, how can I get the best precision on a budget (a few thousand dollars)? I don't care at all about speed (if it takes hours or even days, fine). The materials involved are hard (steel or bronze) and in order to get small feature size, small diameter cutters will be involved (with the problem of easily breaking).
Some thoughts:
Would using stepper motors with very high gear ratios be an option? Or would the belts create too much backlash?
I was thinking about using an off-shelf rotary tool (e.g. a Dremel) for the spindle but I am not sure it would be good enough (run-out, rigidity, etc.)
Are there already commercial machines that do this, and if so, how?
Any help or suggestions would be greatly appreciated!