Damper for a cutting tool

A cutting tool includes a blade, a seat, a shank and a damper. The blade is connected to the seat. The seat is connected to the shank. The shank includes a pocket defined therein and a thread formed on the wall of the pocket. A damper is inserted in the pocket. The damper includes a thread formed on the periphery for engagement with the thread of the shank, with a small gap defined between the threads.

BACKGROUND OF THE INVENTION

The present invention relates to a cutting tool and, more particularly, to a damper for a cutting tool.

During an operation of cutting a work piece with a cutting tool, vibration inevitably occurs and affects the precision of the operation. It is therefore a practice to reduce the vibration by inserting a damper within a shank of the cutting tool.

Dampers have been disclosed in documents such as Japanese Patent Application Publication Nos. 2001-96403, 2003-62703, 2003-136301, 2005-177973, 1994-31505 and 1994-31507 and Japanese Patent Publication No. 2979823.

Japanese Patent Application Publication No. 2003-136301 discloses a cutting tool including a blade attached to a front end of a shank. A deep hole is defined in the shank. The deep hole includes an open end at a rear end of the shank and a closed end near the front end of the deep hole. A damper is inserted in the deep hole, adjacent to the blade. A super hard core is inserted in the deep hole, behind the camper.

Japanese Patent Application Publication No. 1994-31507 discloses a cutting tool including a shank. Viscous fluid and a balancing block are introduced into a deep hole defined in the shank.

Japanese Patent Publication No. 2979823 discloses a helical spring inserted in a deep hole defined in a shank of a cutting tool and a viscous elastic material provided between the helical spring and a closed end of the deep hole. A blade is attached to the helical spring. A frictional, vibration-absorbing material is provided between the blade and the shank for transforming vibration into heat that can be dissipated, thus reducing the vibration.

In each of the foregoing references, it is difficult to make the deep hole in the shank where the external diameter of the shank is small. It requires a deep-hole drill to make the deep hole in the shank, and this is expensive. Moreover, the deep hole compromises the strength of the shank. Moreover, the structure is complicated and entails a high cost.

Japanese Patent Application Publication No. 1994-31505 discloses a shank including a bore defined therein for receiving a damper made of a different material. Friction between the shank and the damper reduces the vibration.

Japanese Patent Application Publication Nos. 2001-96403 and 2003-62703 both disclose a damping material introduced into a bore defined in a shank of a cutting tool. The damping material absorbs the energy of the vibration, thus reducing the vibration. In addition to the foregoing problems, these references involve the use of the damping material including Mn—Cu alloys that are often expensive and cannot be fabricated easily. Therefore, it is difficult to reach a high performance at a low cost according to these references.

Japanese Patent Application Publication No. 2005-177973 is intended to provide a cutting tool with excellent damping at a low cost by making a polygonal pocket in a shank of a cutting tool, inserting a damper in the pocket and closing the pocket with a cover, thus keeping the damper in the pocket. The damper can be strip-like, cylindrical or polygonal. The damper is not connected to the shank, with a gap between them. During an operation of cutting a work piece with the cutting tool, the damper alternatively hits different portions of the wall of the pocket because of inertia, thus reducing vibration. The effect of the reduction of the vibration depends upon the gap. The effect of the reduction of the vibration is poor if the gap is too small or too big. It is however difficult to keep the gap within an appropriate range.

Thus, there is a need for an inexpensive and effective damper for a cutting tool.

BRIEF SUMMARY OF THE INVENTION

The present invention satisfies this need and solves other problems in the field of cutting tools by providing, in a preferred form, a cutting tool with a blade, a seat, a shank and a damper. The blade is connected to the seat. The seat is connected to the shank. The shank includes a pocket defined therein and a thread formed on the wall of the pocket. A damper is inserted in the pocket. The damper includes a thread formed on the periphery for engagement with the thread of the shank, with a small gap defined between the threads.

Where used in the drawings, the same numerals designate the same or similar parts. Furthermore, when the terms “first”, “second”, “lower”, “upper”, “inner”, “outer”, “side”, “end”, “portion”, “section”, “longitudinal”, “axial”, “radial”, “circumferential”, “centrifugal”, “lateral”, “horizontal”, “vertical”, “annular”, “outward”, “inward”, “spacing”, “clockwise”, “counterclockwise”, “length”, “width”, “height”, and similar terms are used herein, it should be understood that these terms have reference only to the structure shown in the drawings as it would appear to a person viewing the drawings and are utilized only to facilitate describing the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIGS. 1 to 4, a cutting tool100includes a blade unit, a shank20connected to blade unit and a damper30movably inserted in shank20according to a first embodiment of the present invention. The blade unit includes a blade12and a seat10. Seat10includes a shank-connecting portion11formed at an end and a blade-connecting portion14formed at an opposite end. A thread13is formed on shank-connecting portion11of seat10. Blade12is detachably connected to blade-connecting portion14of seat10.

Shank20is a hollow element with a pocket21axially defined therein. A thread22is formed on the wall of pocket21corresponding to thread13.

Damper30includes a rod31, a thread32formed on the periphery of rod31corresponding to thread22and a groove33defined in an end of rod31. Damper30is inserted in shank20by engaging thread32with thread22. A flat tip of a screwdriver can be inserted in groove33, and the screwdriver is therefore operable to rotate damper30. The length of rod31is shorter than the depth of pocket21so that damper30can be inserted in shank20completely. Seat10is connected to shank20by engaging thread13with thread22. As indicated with “A”, welding is used to secure seat10to shank20, thus retaining damper30within shank20.

There is intended to be a gap S between an end of rod31and a closed end of pocket21and another gap S between an opposite end of rod31and shank-connecting portion11of seat10. There is intended to be a gap D between the threads22and32. The width of gap D is 0.01 to 0.5 mm. As indicated with arrow heads W, damper30is moved relative to shank20because of inertia when cutting tool100cuts a work piece, thus causing vibration. The forces exerted on damper30and shank20by each other can be dispersed as indicated with arrow heads P, i.e., in directions perpendicular to interfaces between thread32and22. The vibration can effective be reduced since Gap D is small and the density of damper30is larger than that of shank20.

Referring toFIG. 5, there is shown a cutting tool100according to a second embodiment of the present invention. The second embodiment is identical to the first embodiment except two things. Firstly, an elastic element such as a leaf spring40is secured to the closed end of pocket21by welding and compressed between an end of rod31and a closed end of pocket21. Secondly, another leaf spring40is secured to shank-connecting portion11of seat10by welding and compressed between an opposite end of rod31and shank-connecting portion11of seat10. Leaf springs40are useful for restricting the movement of damper30within a small range centered at a middle point of pocket21. Therefore, the proper operation of damper30within shank20is ensured.

Referring toFIGS. 6 and 7, there is shown a damper50according to a third embodiment of the present invention. Damper50includes a shell51, a core52inserted within shell51and a cover53secured to shell51, thus retaining core52within shell51. Shell51is in the form of a hollow cylinder, with a chamber54defined therein. A thread55is formed on an external side of shell51. An internal side of shell51(or “the wall of chamber54”) is smooth.

Core52is in the form of a solid cylinder with a smooth periphery. The density of core52is larger than that of shell51or shank20within which damper50is inserted. Core52is fit in chamber54.

Cover53includes a groove56defined in a side thereof. Cover53is preferably in the form of a plug fit in shell51, with groove56exposed to the exterior of shell51. Furthermore, welding is used to secure cover53to shell51.

Damper50is inserted in shank20by engaging thread55with thread22. A flat tip of a screwdriver can be inserted in groove56, and the screwdriver is therefore operable to rotate damper30. The third embodiment is like the first embodiment except using the three-piece configuration instead of the one-piece configuration.

Referring toFIG. 8, there is shown a cutting tool100according to a fourth embodiment of the present invention. The fourth embodiment is identical to the third embodiment except two things. Firstly, an elastic element such as helical spring41is welded to the closed end of pocket21and compressed between an end of damper50and a closed end of pocket21. Secondly, another helical spring41is welded to shank-connecting portion11of seat10and compressed between an opposite end of damper50and shank-connecting portion11of seat10. Helical springs41are useful for restricting the movement of damper50within a small range centered at a middle point of pocket21. Therefore, the proper operation of damper50within shank20is ensured.

Referring toFIG. 9, there is shown a cutting tool100according to a fifth embodiment of the present invention. The fifth embodiment is like the fourth embodiment except including a restricting device60for restricting the movement and rotation of damper50within shank20. Restricting device60includes a rib61and a pin62. Rib61is formed at an end of shank-connecting portion11of seat10. The size of rib61is smaller than that of groove56, thus allowing rib61to be inserted in groove56, thus restricting the rotation of damper50within shank20within a small range. Pin62is fit in a recess64defined in damper50through an aperture63defined in shank20, thus restricting the rotation of damper50relative to shank20within a small range. Recess64can extend in shell51only, or extend to core52, or extend throughout shell51and core52.

It should be noted that damper50moves for a distance equal to the pitch of thread55while damper50and therefore pin62rotate for 360 degrees. As the rotation of pin62is restricted within a small angle such as 5 degrees, the movement of the pin62and therefore damper50is limited within a very small range centered at the middle point of pocket21.

Referring toFIG. 10, there is shown a cutting tool100according to a sixth embodiment of the present invention. The sixth embodiment is like the first embodiment except including the rib61of the fifth embodiment.

Referring toFIG. 11, there is shown a cutting tool according to a seventh embodiment of the present invention. The seventh embodiment is like the second embodiment except including the pin62of the fifth embodiment.