Grinding of highly accurate hourglass worm gears — trial manufacture of the worm grinding device

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Highly accurate worm gears can be effectively used as an angle standard. Wildhaber worm gearing is a kind of hourglass worm gearing, which owing to its geometrical simplicity, can have its worm and worm wheel easily finished and accurately measured. This study describes a precision grinding method of the Wildhaber worm. A hobbing machine can cut hourglass worms, but cannot give them higher accuracy than the master worm gears. To overcome this limitation, a special grinding device has been made. The main features of this grinding device are as follows: the linear motion of the ball screw gives a very accurate circular feed to the grinding spindle, and the device has no mechanical connection between that circular feed and the rotation of the workpiece. In the first place, the working accuracy of the device was measured. The rotational accuracy of the rotary table relative to the worm was 1 second of arc. The accuracy of the ground worm using this device was 1.2 second of arc.