A new type of hourglass worm gearing is developed by the authors’ own theories [1], [2]. This hourlgass worm gearing has the good points of Hindley’s one and also covers the weak points of it. The worm is cut by a tool with straight-lined cutting edge which is fixed to the basic member [1]. The tooth of the worm has the secondary action, and the wheel tooth consists of two kinds of surfaces. The wheel tooth surface which is concerned to the secondary action of the worm has the same character with the enveloped surface of the Hindley’s wheel [2]. Thus this worm gearing has two characteristics of contact. One is recognized as the contact lines lying perpendicularly to the relative sliding velocity. The other is recognized as the contact lines of constant slide-roll ratio. That is, the worm tooth surface and a part of the wheel tooth surface contact with each other with constant slide-roll ratio. The gears manufactured by the authors showed an efficiency of over 80 percent and the wear of the wheel tooth surface was less than that of Hindley’s one.

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