Rotating Nut Ball Screw for dual X axis

[AeroKam]

I am tring to decide between Ball Screw or Rack and Pinion for the Drives on a 6' X 4' CNC router table.

Accuracy as well as cost is important!

Rack and Pinion seems to be a cheeper option but accuracy is lacking. I have thought of using a 20mm Rolled Screw fixed at either end and then rotating the nut to provide the motion. Thus whip should not be a problem.

Is this a sound approach to this problem?

[ger21]

Rack and poinion can be very accurate if done correctly. You just need to gear it down to get the required resolution, and use some method of keeping the pinion tight to the rack.

Rotating the nut will work great if you can fabricate all the necessary parts to make it work. Our $100K plus router/machining center uses a rotating nut on a 12' screw.

[AeroKam]

Thanks Gerry,
The main problem in Australia is we do not have access to cheap CNC parts. ie it cost me $Aus4000 for 2x2400mm/thk sr25 and 2x1500mm thk sr15 Linear rail.

I am thinking of buying Rack and Pinion from Mcmaster.com Do you know if their Rack is of a suitable accuracy? - they seem very economical.
If I can achieve 0.004" per foot I would be happy with rack and pinion.

regards, Bruce