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lead screw diameters for ball vs acme.

Gos

Aluminum
Joined
Oct 14, 2008
Location
Western Washington
In the world of milling machine lead screws:

When going from Acme to Ballscrew, are the ballscrews a smaller diameter than what the Acme screws were, or the same diameter for both?

Still plugging away on an old mill.
Thanks,
Gos
 
Hello:
My 20 HP American Pacemaker lathe uses a 1 1/2 diameter lead screw. The NSK ball screw on the 7 1/5 HP bridge mill is also roughly 1 1/2 inches in diameter. The only thing these two machines have in common is the unsupported span of the screw. My conclusion is that the machine tool designers select a lead screw diameter based on the maximum allowable static deflection of the screw due to gravity.

The axial loads are too low to make shaft buckling a concern.

In a modern machine with very high rapid speeds the screw deflection due to shaft whirl might become a concern.

A third consideration is the fatigue life of the ball screw. The stresses on the ball screw threads are much higher than those on a Acme thread due to the point loading of the circulating balls. For machines designed for a very long service life I would expect that the ball screws would have a diameter larger than that required to limit static deflection.
 








 
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