GB2048134A

GB2048134A - Machine tool center

Info

Publication number: GB2048134A
Application number: GB8013799A
Authority: GB
Original assignee: Cams SpA
Current assignee: Cams SpA
Priority date: 1979-04-26
Filing date: 1980-04-25
Publication date: 1980-12-10
Also published as: FR2454863A1; DD150164A5; SE8003168L; IT7953216V0; FR2454863B3

Abstract

A center for machine tools comprises a shaft (16) rotatably supported in a support body (12) which has a frusto-conical external surface over its entire length, the shaft having a pointed front end (26) projecting beyond the support body and being supported within the body by rolling bearings including a composite rolling bearing at the front end of the support body comprising needle rollers (38) for transmitting radial loads and needle rollers (40) for transmitting axial loads. <IMAGE>

Description

SPECIFICATION Center for machine tools The present invention relates to centers for machine tools.

More particularly, the invention concerns a machine tool center of the type comprising a support body having an at least partly frusto conical outer surface, and a shaft mounted rotatably in the support body and having a pointed front end projecting from said body, the said shaft being supported adjacent its ends by rolling bearings for transmitting radial loads and being further supported adjacent its front end by a rolling bearing for transmitting axial loads.In such centers the support body is provided at its front end, adjacent the frusto-conical outer surface, with a head which receives a radial thrust ball bearing and an axial thrust ball bearing, such centers being commonly referred to as "ballbearing centers The known type of ball-bearing center suffers from the disadvantage that the head of the support body can present a considerable obstacle to tool movement in use of the center in a machine tool.

The object of the present invention is to provide a center for machine tools which avoids the aforementioned disadvantage by having a reduced external diameter, for a given size, compared with known ball-bearing centers.

According to the present invention there is provided a center for machine tools of the type referred to, characterised in that the support body has a frusto-conical external surface over its entire length and in that the two rolling bearings which support the front end of the shaft are of the needle roller type. Preferably the needle roller bearings which support the front end of the shaft have a common outer race member forming part of a composite rolling bearing including needle rollers which transmit axial loads and which bear against a flange on the shaft.

The invention will be further described by way of example, with reference to the accompanying drawing, which is a diagrammatic longitudinal section of a machine tool center according to one embodiment of the invention.

Reference numeral 10 indicates generalty a center for a machine tool, particularly for a lathe, including a support body 12 adapted to be attached to a support structure, such as a tailstock, carried by the machine tool. The support body 12 has an external frusto-conical surface which extends over the whole length of the body.

The support body 12 is tubular and has a cylindrical axial bore 14 in which a shaft 16 is rotatably mounted. A cylindrical counterbore 18 is formed in the larger diameter end of the support body 12 and a cylindrical cavity 20, of smaller diameter than that of the counterbore 1 8 and of greater diameter than the bore 14, interconnects the bore 14 and the counterbore 18. An annular shoulder 22 is formed between the counterbore 18 and the cavity 20 and is perpendicular to the longitudinal axis of the center 10. At its smaller diameter end the support body 12 is formed with a cylindrical counterbore 24 of greater diameter than the bore 14.

The shaft 16 has an end portion 16a of enlarged diameter which projects beyond the end of the support body 12 and which terminates in a conical point 26. A flange 28 is formed on the shaft 16 at the end of the enlarged portion 16a remote from the point 26.

The shaft 16 is supported at its rear end by a radial thrust needle roller bearing 30 which is housed within the cylindrical counterbore 24. The bearing 30 is retained axially by a nut 32 which is screwed into a threaded end portion of the counterbore 24.

The shaft 16 is supported at its front end by a composite needle roller bearing 34 which transmits both axial and radial loads. The bearing 34 has a profiled outer race 36 which is common to the axial and radial load transmitting rollers and which abuts both the cylindrical wall of the cavity 20 and the adjacent annular shoulder 22. The bearing 34 comprises a plurality of needle rollers 38 which transmit radial loads and which roll on a hardened track formed directly on the shaft 16, and a plurality of needle rollers 40 which transmit axial loads and which run on a radial face of the flange 28. The flange 28 is trapped axially by an externally threaded ring 42 which is screwed into a threaded end portion of the counterbore 18.

Thanks to the reduced size of the compound bearing 34 the center 10 does not have the enlarged head which was necessary in centers used hitherto in order to accommodate thrust ball bearings. This avoids obstruction to tool movement which is a disadvantage of such known ball-bearing centers.

1. A center for machine tools, comprising a support body having an external surface which is frusto-conical over its entire length and a shaft mounted rotatably in the support body and having a pointed front end projecting from said body, in which the shaft is supported adjacent its ends by rolling bearings for transmitting radial loads and being further supported adjacent its front end by a rolling bearing for transmitting axial loads, the two rolling bearing which support the front end of the shaft being of the needle roller type.

2. A center according to Claim 1, in which the needle roller bearings which support the front end of the shaft have a common outer race member forming part of a composite rolling bearing including needle rollers which transmit axial loads; and which bear against a flange on the shaft.

3. A center according to Claim 2, in which the support body is formed, at its end adjoining the pointed end of the shaft, with a cylindrical counterbore and a cylindrical cavity having a diameter smaller than that of the counterbore und adjoining the latter by way of an annular radial shoulder which is perpendicular to the longitudinal

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Center for machine tools The present invention relates to centers for machine tools. More particularly, the invention concerns a machine tool center of the type comprising a support body having an at least partly frusto conical outer surface, and a shaft mounted rotatably in the support body and having a pointed front end projecting from said body, the said shaft being supported adjacent its ends by rolling bearings for transmitting radial loads and being further supported adjacent its front end by a rolling bearing for transmitting axial loads.In such centers the support body is provided at its front end, adjacent the frusto-conical outer surface, with a head which receives a radial thrust ball bearing and an axial thrust ball bearing, such centers being commonly referred to as "ballbearing centers The known type of ball-bearing center suffers from the disadvantage that the head of the support body can present a considerable obstacle to tool movement in use of the center in a machine tool. The object of the present invention is to provide a center for machine tools which avoids the aforementioned disadvantage by having a reduced external diameter, for a given size, compared with known ball-bearing centers. According to the present invention there is provided a center for machine tools of the type referred to, characterised in that the support body has a frusto-conical external surface over its entire length and in that the two rolling bearings which support the front end of the shaft are of the needle roller type. Preferably the needle roller bearings which support the front end of the shaft have a common outer race member forming part of a composite rolling bearing including needle rollers which transmit axial loads and which bear against a flange on the shaft. The invention will be further described by way of example, with reference to the accompanying drawing, which is a diagrammatic longitudinal section of a machine tool center according to one embodiment of the invention. Reference numeral 10 indicates generalty a center for a machine tool, particularly for a lathe, including a support body 12 adapted to be attached to a support structure, such as a tailstock, carried by the machine tool. The support body 12 has an external frusto-conical surface which extends over the whole length of the body. The support body 12 is tubular and has a cylindrical axial bore 14 in which a shaft 16 is rotatably mounted. A cylindrical counterbore 18 is formed in the larger diameter end of the support body 12 and a cylindrical cavity 20, of smaller diameter than that of the counterbore 1 8 and of greater diameter than the bore 14, interconnects the bore 14 and the counterbore 18. An annular shoulder 22 is formed between the counterbore 18 and the cavity 20 and is perpendicular to the longitudinal axis of the center 10. At its smaller diameter end the support body 12 is formed with a cylindrical counterbore 24 of greater diameter than the bore 14. The shaft 16 has an end portion 16a of enlarged diameter which projects beyond the end of the support body 12 and which terminates in a conical point 26. A flange 28 is formed on the shaft 16 at the end of the enlarged portion 16a remote from the point 26. The shaft 16 is supported at its rear end by a radial thrust needle roller bearing 30 which is housed within the cylindrical counterbore 24. The bearing 30 is retained axially by a nut 32 which is screwed into a threaded end portion of the counterbore 24. The shaft 16 is supported at its front end by a composite needle roller bearing 34 which transmits both axial and radial loads. The bearing 34 has a profiled outer race 36 which is common to the axial and radial load transmitting rollers and which abuts both the cylindrical wall of the cavity 20 and the adjacent annular shoulder 22. The bearing 34 comprises a plurality of needle rollers 38 which transmit radial loads and which roll on a hardened track formed directly on the shaft 16, and a plurality of needle rollers 40 which transmit axial loads and which run on a radial face of the flange 28. The flange 28 is trapped axially by an externally threaded ring 42 which is screwed into a threaded end portion of the counterbore 18. Thanks to the reduced size of the compound bearing 34 the center 10 does not have the enlarged head which was necessary in centers used hitherto in order to accommodate thrust ball bearings. This avoids obstruction to tool movement which is a disadvantage of such known ball-bearing centers. CLAIMS

3. A center according to Claim 2, in which the support body is formed, at its end adjoining the pointed end of the shaft, with a cylindrical counterbore and a cylindrical cavity having a diameter smaller than that of the counterbore und adjoining the latter by way of an annular radial shoulder which is perpendicular to the longitudinal axis of the support body, and in which the common outer race member of the front bearings abuts both the cylindrical wall of the cavity and the said annular shoulder, the flange on the shaft being retained axially by a threaded ring screwed into a threaded end portion of the said counterbore.

4. A machine tool center substantially as herein described with reference to and as shown in the accompanying drawing.