The lead screws on my chester mill have a 5mm pitch i think. As for precision it depends what kinda work im doing, if im just drilling holes in flat plate (basicaly just useing the table to eaqualy space out a row of say 5 holes) i get accurate results but if im milling and puting side force on the cutter accuracy is not so good. im useing mach3 and the backlash comp is set to about 0.13 mm (cant remember exactly), backlash comp is only a last resort and doesnt substitute for a good solid mechanical set up. also the lead screws have 2 ball thrust bearings near the handles and thease dont cope well with the radial force put on them by the belt tension. as i said this was a tempary conversion and just wanted to CNC it as fast and cheeply as poss. you will probly find yourself switching to ballscrews soon after you have done the cnc conversion but no harm in giveing it a go with the standard screws and see how it goes. cool thing with ballscrews is not only the minimal backlash but you only lose about 5% of your motors torque in the nut where as with norm screws you use around half your motors torque just in the friction of the nut/screw.


Oh and the max feed rait i get on my set up is 800mm/min not 1800 as i said in a previous post, musta had my mini lathe in mind when i said 1800


regards
Simon