ballscrew suggestion

[eloid]

planing on a 72" wide gantry with 5/8 ballscrew .2 pitch
is 5/8 diameter to small for ballscrew this length?
the z axis would be sliding gantry with hiwin guide rails...
cutting mainly wood and light alum. so cuts would not super fast?

[LazyMan]

I suspect a screw that long at only 5/8 would not suffice unless you wanted to really run your machine pretty slow. I dont think it would be practical though. Also some manufactures max length for a 5/8 ballscrew is 72"

Im currious, how big of a machine are you planning to build?

[harryn]

The posters on the forum often recommend using a fixed screw and rotating ballnut that kind of length. Cutting speed affects finish, so dont get to cornered with low speed ideas. Try cutting with your router manually at different speeds and see what finish you like.

[LeeWay]

There is a mechanism that you can design in that would help with whip on a screw this long. I have heard of them, but not actually seen one. Imagine a fork or padded channel. It will support the screw directly. When you approach the center of the screw with the ball nut, it pushes a cam and the fork retracts while you are in the area. If you go past the middle to the other side, the cam releases and the for re engages. Same for the other direction. This way the center of the screw is semi supported on three sides and it won't whip. The fork would need to be spring loaded. You could even use a pneumatic actuator to control it. Just a little air operated toggle clamp. It sounds a little complicated, but really quite simple.
When you start getting higher in size than 5/8" @ this length, you are getting into some serious cash.