Hi,
what are your existing lead screws?
If you are serious about CNC and making fast and accurate machines then consider ballscrews. Rolled ballscrews are reasonably cheap and
have an accuracy of 50um per 300mm. Ground ballscrews are way WAY more expensive, C5, the entry level ground grade is 18um per 300mm
right up to C1 grade for semiconductor machines made to special order.
garylucas is correct a pitch of 0.2 inch or 5mm is about right, you still get good mechanical advantage obviating the need for gearboxes without
having to spin them at blinding speeds to get useful rapids.
Craig