| 摘要 |
Apparatus for boring and surfacing, with automatic advance and withdrawal, in which the displacements of a carriage (4) carrying a tool are effected via a drive screw (12), this screw being driven by a system comprising at least one ratchet wheel (13, 14) driven by a pawl (20, 21) which rotates it, for each revolution of the apparatus, by an angle corresponding to the space in between two teeth of the ratchet wheel. There are preferably two ratchet-wheel and pawl systems, one for the advance of the carriage and the other for the withdrawal, and a tilting mechanism activates one or the other depending upon the direction of rotation of the apparatus. <IMAGE>
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