| 摘要 |
A top housing supported by a vertical post in a drilling machine is provided with a belt transmission mechanism incorporating a speed adjusting mechanism which can be operated easily and manually. The adjusting mechanism includes a knob connected to an adjusting rod which in turn is connected to a movable cone-shaped disk. The adjusting rod has a helical thread engaging with a projection of a fixed annular seat through which the adjusting rod passes. The adjusting rod is moved axially when rotated and moves the movable cone-shaped disk with respect to a fixed cone-shaped disk. A locking nut is threadedly sleeved around the annular seat to prevent the adjusting rod from rotation when the nut is tightened. The top housing is mounted movably on the vertical post and normally moved upward by a compression spring. A rack-and-pinion mechanism is associated with the top housing and the vertical post so that the top housing can be moved downward by operating a handle which is connected to the rack-and-pinion mechanism.
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