5/8 Ballscrew Critical speed

[LazyMan]

Im trying to pick a screw for a machine and im stumped. I used nooks critical speed calculator and with a .5" root dimater and 48" from bearings it will give 372rpm. That seems low as this would allow for a max speed of 75 IPM with a .2 lead. I have read other posts of people running 5/8 screws at 800RPM. What am I missing here?


EDIT

Oops, I did not have the correct fixity selecte. I should be able to get around 1000rpm with a 48" screw. Does this seem like a realistic figure?

[fseger]

your didn't specify the length of screw. But for about 4' that seems right. On my DIY, I have 5/8" x .2 roton ballscrews about 54" between bearings. I don't have the "proper" setup with thrust bearings, just some needle bearings and radial bearings put together temporarily. I can move mine machine about 150-200 IPM before they start to whip. As you move closer to the center of travel you can move faster.