US Patent: 2,849,929
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| Broaching Attachment
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Patentee:
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| Harold C. Thorstens (exact or similar names) - Rockford, IL |
| Manufacturer: |
| Not known to have been produced |
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Patent Dates:
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| Applied: |
May 09, 1955 |
| Granted: |
Sep. 02, 1958 |
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Joel Havens
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Description: |
| McCanna & Morsbach - patent attorneys
This invention relates to a broaching apparatus and more particularly to a broaching attachment for use on screw machines and the like. In the formation of articles requiring machining operations which can be performed on automatic screw machines as well as a broaching operation, it has been found more expedient to also form the broaching operation on the screw machine wherever possible. Such machines, however, are not primarily designed for broaching and when conventional broaching apparatus are used on these machines, frequent failures have occurred in the mechanism for extending and retracting the turret slide. When the turret slide is extended to force the broach into the workpiece, the broach and turret travel at least a short distance before engaging the workpiece and consequently the inertia of the turret slide is overcome before the broaching operation is started. After the turret has begun its extending movement, it has been found that the turret slide operating mechanism is adequate to thereafter extend the broach into the workpiece, the inertia of the moving slide assisting in carrying the broach into the work. However, when retracting the broach from the broached hole in the workpiece, the frictional drag of the broach on the workpiece as well as the inertia of the turret slide must be overcome by the slide operating mechanism. This combined load has been found to overload the slide operating mechanism and cause relatively frequent failures in the operating mechanism which require repairs that are costly due both to the parts and labor required as well as to the prolonged time during which the machine must remain idle for the repairs. In such screw machines, the other machine operations are generally performed while the workpiece is rotating. In order to permit broaching without stopping the workpiece, the broach is arranged to rotate with the workpiece during the broaching operation. It has heretofore been proposed to rotatably support the broach holder and move the broach into engagement with a rotating workpiece to cause the broach and broach holder to rotate in unison with the workpiece. However, because of the large mass of the broach holder, the latter could not be rapidly brought up to the speed of the workpiece without imposing high torsional stresses on the broach which tends to damage the broach and workpiece. It is an important object of this invention to provide a novel broaching attachment, which enables retracting of the broach from the workpiece without imposing excessive loads on the turret slide operating mechanism. Another object of this invention is the provision of a broaching attachment having an improved construction for effecting rotation of the broach in unison with the workpiece to permit the broaching operation to be rapidly performed on rotating pieces. Another object of this invention is the provision of an improved rotary support for the broach. A more particular object of this invention is the provision of a broaching attachment including a housing and # broach holder, in which the broach is rotatably supported in the broach holder so as to rotate relative thereto upon initial contact of the broach with the workpiece, and in which the broach holder is rotatably supported in the housing by thrust bearings so as to thereby rotate with the broach as pressure is applied to the broach to urge it into the workpiece. An additional object of this invention is the provision of a broaching attachment in which the broach is mounted for limited axial lost motion to enable partial retraction of the broaching attachment away from the work piece before retraction of the broach is started, whereby the turret slide operating mechanism does not operate against the frictional drag of the broach until after the inertia of the turret and turret slide has been overcome and the latter is moving in a direction to retract the broach.
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