BALLSCREWS QUESTION

I'm older to this list but this is my first question to the forum.
I'm looking at putting together my own CNC mill. I already have two
superb 40" german x/y linear assemblies and the servo motors (54V, 7A,
3000 RPM), everything saved from junk. I intend to use Gecko 340 and
Mach2.

The question I have regards to the TPIs of my ballscrews –they are
20mm - (0.8") - per revolution. This seems very large to my purpose.

I would like to know if some of you kind folk would take a moment to
figure the way I can use it with a minimum of acurracy, say 0,01mm,
using belt reduction, I guess.

Thanks very much,

Manel Miranda
Braga, Portugal