PMI’s (Precision Motion Industries’) high slenderness ratio Ground Ballscrews with Rotary Nut can be used at high feed speed without causing inertia. PMI is represented in India by Superslides & Ballscrews Co. India Pvt. Ltd.
In the past, with long ballscrew assemblies, the nuts couldn’t react immediately. A rotary nut can have a high feed speed with high lead and still achieve accuracy. The design of the screw shaft journal can be simplified because it does not need support bearings.
Roller thrust bearings must be installed on rotary nuts because the support bearing is larger than the regular bearing. Hence the rigidity in the shaft direction has been increased.
It is possible to lubricate the ballscrew and the bearing installed on rotary nuts at the same time.
Lubrication for rotary nuts is complicated since rotating unions are necessary to feed lubricant directly into the nut, and centrifugal forces push all lubricant away from the balls and groove.
The design of the nut’s end face can be directly secured by the use of the timing pulley.
The ballscrews find applications in Gantry Type Machining Centers, Bridge Type Machining Centers, Double Column Surface Grinders and so on.