| 摘要 |
It is often necessary to fasten bolts in bores of marble tread plates of overhanging stairs and also other workpieces made of a similar material, for example connect two successive tread plates. The invention describes devices, by means of which it is possible to mill in the side wall of such bores designed as a blind hole helical threads into which correspondingly shaped adaptors, especially coupling members for two successive tread plates, can then be screwed. In a device for milling this helical groove, the spindle of the milling cutter (14) is driven by a motor (9) which is carried on a frame (1) attachable to the constructional part, the cutter axis being mounted so that it forms an acute angle with the axis of the bore (15). Provided on the frame (1) is a guide piece (3) which carries a screw thread (4) and which is arranged rotatably relative to the counterpiece (5) carrying a corresponding counterthread and connected firmly to the frame. The arrangement is such that, as a result of the rotation of a handle piece (17) and the helical movement of the counterpiece (5), a mounting of the cutter axis is so pivoted or moved on a circular path that the cutter axis (13) describes a helical surface (Fig. 1). <IMAGE>
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