Cutlery – Cutting tools – Saw
Reexamination Certificate
1999-10-25
2001-08-21
Watts, Douglas D. (Department: 3724)
Cutlery
Cutting tools
Saw
C279S904000
Reexamination Certificate
active
06276065
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a blade attaching and detaching mechanism for saber saws. Various saber saws have been conventionally developed to cut or saw woody or steel materials or pipes in the housing or building construction sites or similar fields.
The saber saw is a cutting tool with a reciprocating plunger driven by an electric motor. A blade has an engaging hole engageable with the plunger.
The normal size plungers have a reciprocating stroke of approximately 20 mm to 32 mm. In actual cutting or sawing operations, the blade is locally worn at the limited region corresponding to the reciprocating stroke. Especially, blades are frequently broken during the cutting operation of a steel member. A long blade tends to be broken at its proximal end closer to the plunger. In many cases, the blades are broken and the user is forced to exchange the blades frequently.
To exchange the blades, using a wrench or a specialized tool is popular. However, using the wrench or specialized tool is inefficient because it takes a long time to complete the attaching or detaching operation. Moreover, the user may lose the wrench or specialized tool.
U.S. Pat. Nos. 5,443,276; 5,575,071; 5,647,133; and 4,299,402 disclose toolless blade attaching and detaching mechanisms capable of exchanging the blades without using a wrench or similar tool.
For example, U.S. Pat. Nos. 5,443,276; 5,575,071; and 5,647,133 disclose the toolless blade attaching and detaching mechanisms having a steel ball or a movable locking pin which is engageable with a hole of the blade. A lever or a rotary ring is provided to hold the attached blade or to disengage the steel ball or the movable locking pin from the blade.
However, these conventional toolless blade attaching and detaching mechanisms basically force the use to touch the blade for removing the blade or its broken piece. During the removing operation, the sharp edge of the blade may injure the user's hand. The blade surface has a high temperature due to friction during the cutting or sawing operation. The user's hand may be burned by the heated blade surface.
When the blade is broken at the proximal end, a small piece of the blade will be left in a narrow space of the plunger. It takes a long time to completely remove such a small piece remaining in the narrow space of the plunger.
According to the toolless blade attaching and detaching mechanisms disclosed in U.S. Pat. Nos. 5,443,276 and 5,575,071, the user is required to hold the lever or the rotary ring at a predetermined unlock position of the locking pin against the resilient force during the blade attaching and detaching operation. In other words, the user must use both hands simultaneously.
Furthermore, the blade has an elongated shape and therefore easily causes a lateral vibration when it reciprocates at a high speed.
The toolless blade attaching and detaching mechanisms disclosed in U.S. Pat. Nos. 5,443,276 and 5,647,133 comprise complicated parts exposed outside the saber saw. This is disadvantageous in that such complicated parts may be damaged by a cut or sawed member during the cutting or sawing operation.
Furthermore, according to the toolless blade attaching and detaching mechanism disclosed in U.S. Pat. No. 4,299,402, it is difficult to press a side surface of the blade. The blade will be subjected to a severe vibration.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a blade attaching and detaching mechanism for a saber saw which is durable and is capable of simply, safely and surely fixing and removing the blade to or from the plunger.
In order to accomplish this and other related objects, the present invention provides a blade attaching and detaching mechanism for a saber saw comprising a plunger for holding a rear end of a blade and reciprocating the blade to perform a cutting or sawing operation. A slit and a bore are formed in the plunger. The slit extends in an axial direction of the plunger. The bore extends in a direction normal to the axial direction of the plunger. The slit and the bore merge with each other. A locking pin is slidably disposed in the bore. The locking pin comprises a projecting portion engageable with a hole formed on the blade, and a surface for pressing a side surface of the blade to a wall of the slit of the plunger. A blade holder is coupled around the plunger and slidable in the axial direction of the plunger. The blade holder shifts in an axially forward direction to generate a pushing force applied to the locking pin. With this pushing force, the locking pin engages with the hole of the blade. Furthermore, the blade holder shifts in an axially rearward direction to release the pushing force applied to the locking pin. The locking pin is disengaged from the hole of the blade.
Preferably, an additional blade holder is provided for slidably holding the blade holder. The additional blade holder prevents the locking pin from being pulled out of the bore when the blade holder shifts in the axially rearward direction.
Preferably, the blade holder has a tapered cylindrical surface expanding in the axially forward direction. The tapered cylindrical surface is brought into contact with the locking pin so as to regulate a shifting position of the locking pin. A contact point between the tapered cylindrical surface and the locking pin changes in accordance with an axial movement of the blade holder. Thus, the pushing force applied to the locking pin is changeable.
Preferably, a resilient member is provided for resiliently urging the blade holder in the axially forward direction.
Preferably, a helical groove is provided on an outer surface of the plunger. The helical groove has a predetermined inclined angle with respect to an axis of the plunger. An engaging member is disposed in the helical groove. The engaging member, such as a steel ball, rolls in the helical groove when the blade holder rotates. Thus, the blade holder is allowed to shift in the axial direction of the plunger.
Preferably, an additional groove is continuously formed with the helical groove. The additional groove is arranged perpendicular to the axis of the plunger.
Preferably, an urging member is provided in the bore of the plunger so as to urge the locking pin in a radially outward direction.
Preferably, a support member is interposed between the resilient member and the plunger.
REFERENCES:
patent: 3927893 (1975-12-01), Dillon et al.
patent: 4299402 (1981-11-01), Hoffman
patent: 5219174 (1993-06-01), Zurbrugg et al.
patent: 5443276 (1995-08-01), Nasser et al.
patent: 5575071 (1996-11-01), Phillips et al.
patent: 5647133 (1997-07-01), Dassoulas
patent: 5903983 (1999-05-01), Jungmann et al.
patent: 6209208 (2001-04-01), Marinkovich et al.
patent: 12-117534 (2000-04-01), None
patent: 13-500795 (2001-01-01), None
Osada Yoshio
Tachibana Toshihiko
Connolly Bove & Lodge & Hutz LLP
Hitachi Koki Co,. Ltd.
Watts Douglas D.
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