HI,l want to use SFU1604-3 model ballscrew with nema 34HS9840 motors.Please tell me steps per,velocity and acceleration.unit is mm.thanks

Steps per unit will depend on both the pitch of your ballscrew and the microstepping selected by your motor driver.

There is a calculator here : http://www.machsupport.com/forum/index.php/topic,16315.0.html
And an example here : http://www.machsupport.com/forum/index.php/topic,12512.0.html

Please also refer to your other posting : http://www.machsupport.com/forum/index.php/topic,34160.0.html

Tweakie.