help with a 4' by 9' cnc build

[phooddaniel]

If you hunt through his site you will find information on BlackToe, his 8' x 4' design using chain drive.

If you want to go with leadscrews you will need a ballscrew of 25mm diameter with fixed bearings at each end holding the screw in tension. With a 5mm pitch this will give you 1200mm/min (50ipm) cutting speed and 3200mm/min (125ipm) rapids (limited by screw whip) using an 8Nm NEMA34 stepper with decent drivers (50 or 60volt drives).

For the short, 4', axis a 16mm x 5mm ballscrew simply supported and a 2Nm motor would suffice.

Quite correct. There have been some interesting ways to stop wild whipping of lead screws, but the expense and efforts are generally futile. Rack and pinion, timing belt and roller chain seem to be the best methods to move at long distances. I have tried with great success both the roller chain (at #40 size) and timing belt. My intension was to try to eliminate as much mechanical backlash as possible and these two really do the trick. Rack and pinion, although the best for the longest distances, can still exhibit some backlash due to the possibility of space between the two gears. Backlash is almost eliminated since the roller chain and the timing belt are both tensioned and the drive pulley/sprocket are fastened to the motor.

By the way, thanks for supporting the efforts over at buildyourcnc.com. This is my first post on this site.