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Okuma

Published in Galleries on 3/18/2019 by Ballscrew Guys

The Okuma LB15 is a two axis turning center/lathe which uses a ball nut mounted to the head (Z axis) that rides on a ball screw with end bearings on each end, the screw is typically driven by a belt which is housed in a cast box that also acts as the motor support. Over time the factory grease in the end bearings fails due to age, use, and contamination. This will cause delamination and pitting of the races and ball wear which translates into excessive backlash and play at the tool holder. End bearing replacement is a bit involved due to the rather complicated driven pulley for the screw which is used to trip a "shear sensor" for overload protection on top of removal of the belt housing/motor mounting and drive motor. Access of the Z screw and ball nut is done by removing the side covers opposite of the operator side, disconnecting the sliding covers secured to the tool head, and disconnecting the accordion style covers on the screw itself.

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Okuma LB15

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Belt housing/ motor mount

Here you can see the housing that contains the drive belt and pulleys for the Z axis drive.
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Motor side end bearing

Here you can see the housing completely removed and the driven pulley completely disassembled so the end bearing can be accessed.
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Getting to the ball nut

In this picture you can see the back side of the machine housing removed, sliding covers disconnected/ removed, and accordion covers for the screw shaft pulled back so the ball nut can be dismounted from the tool head yoke and accessed for refurbishment. This particular nut is a Tsubaki split style two track nut that uses a fitted shim to "push" the halves apart and make the balls ride on opposing sides of the track on the screw.

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