OSTexo, I appreciate your input on this as well as everyone else.

What I would have expected from the services I have talked to is "We can't do it because ..." with some specifics instead of leaving me to speculate about what the problem is. If they can't qualify the problem to the customer, is that not ignorance?

I'm not overly concerned with a high surface finish or accuracy, and I have clarified this to the services I have communicated with. So despite not needing these things, it appears that most services don't have an easy way to dumb down the process. The optimization and spline interpolation that is maintaining a higher accuracy and surface finish also makes for less wear & tear on the machine.

I am aware that the Jewelry industry, who I would not consider hobbyists, produce work from STL files by milling. In many cases they mill wax although, that has largely gone the way of 3d printing. They also machine small molds for non-investment casting.

There are some "micro" milling machines with a work volume of less than 3", and perhaps part of the difficulty in finding someone to do the work is relevant to the size I require.

I need a minimum of 3" XY, up to perhaps 12" -18" max XY and 2" in Z. I only need 3 axis machine (no undercuts).

Once I get some software to convert polys to nurbs, I'll have another go at this.