Portable cutting machine

An operation member has a higher degree of design freedom in, for example, the position and the amount of displacement of an operation part, and the force used for operation. A portable cutting machine includes a base, an electric motor, a blade rotatable by the electric motor, a movable cover covering a lower part of the blade protruding downward from the base and rotatable to be open, an operation lever located frontward from a rotation center of the blade and rotatable, and a transmission lever rotatable to push and open the movable cover when pushed by the operation lever.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese Patent Application No. 2019-160408, filed on Sep. 3, 2019, the entire contents of which are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present invention relates to a portable cutting machine.

2. Description of the Background

Portable cutting machines commonly have a movable cover covering a blade. The movable cover is rotated to be open. During a cutting operation in which the cutting machine is moved forward to cut into the workpiece, the movable cover is open as it is pushed by an edge of the workpiece facing the movable cover. However, the movable cover may not be open smoothly at the beginning of the cutting operation depending on the material of the workpiece or the manner of cutting. Some cutting machines include a mechanism to manually assist the initial opening of the movable cover. A cutting machine described in Japanese Unexamined Patent Application Publication No. 8-238604 (hereafter, Patent Literature 1) includes a rotatable lever. When the lever is rotated, a wire connected to a movable cover is pulled to open the movable cover. A cutting machine described in Japanese Unexamined Utility Model Application Publication No. 62-162003 (hereafter, Patent Literature 2) includes an operation member that is linearly slidable. When the operation member is pulled, a lever connected to a movable cover is rotated to pull and open the movable cover.

BRIEF SUMMARY

The operability of the cutting machines described in Patent Literatures 1 and 2 is to be improved. For the cutting machine described in Patent Literature 1, the movable cover has the wire anchored near the rotation center of the cover. The lever is operated with a larger force. However, the lever operation part located farther from the rotation center of the lever is to be displaced by a larger amount to open the movable cover. For the cutting machine described in Patent Literature 2, the operation member is pulled linearly. This operation member cannot be operated easily, for example, with fingers while the user is holding the cutting machine by both hands, lowering the operability. The operation member may have a higher degree of design freedom in, for example, the position and the amount of displacement of the operation part, and the force used for operation.

An aspect of the present invention provides a portable cutting machine, including:

a base;

an electric motor;

a blade rotatable by the electric motor;

a movable cover covering a lower part of the blade protruding downward from the base, the movable cover being rotatable to be open;

an operation lever located frontward from a rotation center of the blade, the operation lever being rotatable; and

a transmission lever rotatable to push and open the movable cover when pushed by the operation lever.

DETAILED DESCRIPTION

Embodiments of the present invention will be described with reference to the drawings. The same or corresponding components in the embodiments are given the same reference numerals, and will not be described.

Portable Cutting Machine

A portable cutting machine1according to an embodiment is shown inFIGS. 1 to 8. The portable cutting machine1includes a body10and a base3. The base3supports the body10. The body10detachably receives a disk-shaped saw blade (cutting tool)2. The saw blade2is also referred to as a circular saw blade or a tipped saw. The saw blade2rotates using an electric motor20incorporated in the body10as a power supply. For clarity, the saw blade2is not shown in the drawings. InFIGS. 2, 4, and 6, the outline of the saw blade2is drawn using a chain line. The base3includes a window3a(FIG. 3), which vertically extends through the base3. The saw blade2has a lower part extending through the window3aand protruding downward from the base3. To cut a workpiece W, a user moves the portable cutting machine1forward with the base3being placed on the upper surface of the workpiece W. This causes the saw blade2protruding downward from the base3to cut into the workpiece W at an edge near the user.

A portable circular saw will be described as an example of a portable cutting machine according to an embodiment that can be carried by a user as a power tool used for cutting. Other examples of the portable cutting machine include a cutter with a diamond wheel. The portable cutting machine1includes the disk-shaped saw blade (cutting tool)2as described above. A portable cutting machine according one or more embodiments including a rotary blade such as a cutter with a diamond wheel, other than the saw blade2, may have the structure and the features described below.

As shown inFIGS. 1 to 3, the body10includes a loop handle40in its upper portion. The handle40protrudes upward and gripped by the user. The handle40includes a trigger switch lever42on its underside. The switch lever42is pulled with fingers holding the handle40to activate the electric motor20, which rotates the saw blade2. A knob44is located left frontward from the handle40. The knob44protrudes upward and is gripped by the user. During a cutting operation, the user stands behind the portable cutting machine1, holding the handle40with the right hand and gripping the knob44with the left hand, and moves the portable cutting machine1forward. The front and the rear, or the right and the left with respect to the components of the portable cutting machine1are herein defined as the front referring to the direction in which the cutting proceeds, and the rear referring to the direction toward the user.

Cutting Adjustment Unit

A support4is located on an upper front portion of the base3. The body10is supported by a swing support shaft12in a vertically swingable manner relative to the support4. The body10is vertically swingable about the swing support shaft12to change the degree by which the saw blade2protrudes downward from the base3, allowing adjustment of the depth of cutting in the workpiece W with the saw blade2. More specifically, when a lock lever8(FIG. 5) screwed in a stationary cover50is unscrewed, the body10can swing vertically along an arc-shaped depth guide7(FIG. 5) attached to the base3. This allows adjustment of the depth of cutting with the saw blade2attached to the body10. When the lock lever8is screwed into the stationary cover50at an intended position, the depth guide7is fastened to lock the body10on the base3. A support6is located on an upper rear portion of the base3. The body10is supported by tilt support shafts included in the supports4and6at the front and the rear and is thus laterally tiltable relative to the base3. The body10is laterally tiltable about the tilt support shafts to adjust the angle of cutting in the workpiece W with the saw blade2.

Electric Motor

The body10includes the electric motor20. The electric motor20has the rotation axis in the lateral direction. The electric motor20includes a motor shaft for outputting rotational power. The motor shaft has two ends supported in a rotatable manner by bearings fixed on the body housing. A spindle17, to which the saw blade2is attached, extends parallel to the motor shaft. The spindle17is supported in a rotatable manner by bearings fixed on the body housing. A reduction gear train for reducing the rotation from the electric motor20is located between the electric motor20and the spindle17. The spindle17has a distal end protruding into the stationary cover50. The saw blade2is attached to the protruding end of the spindle17. The saw blade2is held between an outer flange2aand an inner flange2d(FIG. 3). The saw blade2is fastened with a fixing bolt2cscrewed into the front face of the spindle17. The saw blade2is thus fixed in a manner nonrotatable relative to the spindle17.

Battery Mount

As shown inFIG. 1, a battery mount30to which battery packs31are attachable is located rearward from the electric motor20. The battery packs31serve as a power supply for the portable cutting machine1. The battery mount30may receive the battery packs31on its lower surface. The battery packs31may each be, for example, a rechargeable lithium-ion battery that is repeatedly usable. In another embodiment, the power tool may use a 100-volt alternating-current (AC) utility power, in place of the battery mount30.

Stationary Cover

As shown inFIGS. 1 to 3, the body10includes the metal stationary cover50. The stationary cover50covers substantially the upper half of the saw blade2. The stationary cover50is substantially semicircular.

The stationary cover50includes a peripheral wall51, a side wall52, and a side wall53. The peripheral wall51covers the periphery of the flat surface of the saw blade2. The side wall52covers an external surface (a surface opposite to the motor) of a cutting edge. The side wall53is integrally connected to the body housing at an internal surface (a surface adjacent to the motor) of the cutting edge. The external side wall52extends radially inward from the peripheral wall51over the external surface of the saw blade2. An arrow52aon the external side wall52of the stationary cover50indicates the rotation direction of the saw blade2.

The stationary cover50includes a dust discharge channel55. The dust discharge channel55extends from an inlet opening in the internal surface of the peripheral wall51of the stationary cover50to an outlet opening at the rear of the stationary cover50. As the saw blade2rotates, dust such as chips from the workpiece W is blown upward, flows rearward inside the stationary cover50in air blow caused by the rotating saw blade2, and is discharged outside through the dust discharge channel55.

Movable Cover

As shown inFIGS. 1 to 3, a movable cover60is attached to the body10. The movable cover60covers substantially the lower half of the saw blade2. The movable cover is formed from, for example, aluminum. The movable cover60is supported in a rotatable manner about the same rotation axis as the saw blade2. The movable cover60is rotated to be open or closed. More specifically, the movable cover60is open first at the front, and then along the bottom toward the rear. As shown inFIG. 2, the movable cover60is open clockwise as viewed from the right of the portable cutting machine1.

The movable cover60includes a peripheral wall61, a side wall62, and a side wall63. The peripheral wall61covers the periphery of the saw blade surface. The side wall62covers an external surface (a surface opposite to the motor) of the saw blade2. The side wall63covers an internal surface (a surface adjacent to the motor) of the saw blade2. The movable cover60is urged in the closing direction by a spring (not shown) to cover substantially the lower half of the saw blade2when the cutting operation is not performed.

The stationary cover50includes a stopper57protruding outward from the side wall53. Urged in the closing direction, the movable cover60at a closed position has the side wall63in contact with the stopper57, and is restricted from rotating any further. When the movable cover60is open against the urging force from the spring, the movable cover60is retracted into a space between the saw blade2and the stationary cover50.

Movement of Movable Cover during Cutting

When the saw blade2cuts into the workpiece W forward with the base3being placed on the upper surface of the workpiece W as shown inFIGS. 2 and 4, the movable cover60is pressed against the edge of the workpiece W near the user and rotates in the opening direction. When the saw blade2cuts into the workpiece W further, the movable cover60is rotated further in the opening direction and moves over the upper surface of the workpiece W. The movable cover60moved entirely over the upper surface of the workpiece W is at an opening position (FIG. 4) of the movable cover60. The movable cover60may also be open manually with a tab65on the movable cover60to the full-open position.

Open Assist Unit for Movable Cover

The movable cover60may not be open smoothly when simply pushed rearward by the workpiece W, depending on the material of the workpiece W or the manner of cutting. In this case, an open assist unit described below can assist the movable cover60to start opening. The open assist unit includes an operation lever70and a transmission lever90. The operation lever70is operable by the user. The transmission lever90transmits the movement of the operation lever70to the movable cover60. The operation lever70and the transmission lever90are both supported by the stationary cover50in a rotatable manner. The operation lever70pushes the transmission lever90to rotate the transmission lever90. The rotating transmission lever90pushes the movable cover60to open the movable cover60.

Operation Lever

As shown inFIGS. 7 and 8, the operation lever70includes a rotational shaft (shaft)71. The operation lever70is supported in a rotatable manner by the rotational shaft71received in a support hole72in the side wall53of the stationary cover50. The operation lever70includes an operation arm73operated with hand by the user. The operation arm73is mounted onto the rotational shaft71outside the stationary cover50. The operation arm73includes an operation part84protruding from its distal end and parallel to the rotation axis. The operation arm73has a recess on its basal end. The recess on the operation arm73has serrations74on its inner peripheral wall. The serrations74are fitted with a hexagon head75of the rotational shaft71. The operation arm73is fastened to the head75of the rotational shaft71with a mount screw76extending through the basal end. The rotational shaft71extends through the stationary cover50, eliminating any slit for receiving the operation arm73in the stationary cover50. This prevents chips from coming out of the stationary cover50through such a slit.

The operation lever70is located frontward from the rotation center of the saw blade2. The operation arm73is particularly located on the right of the knob44as shown inFIG. 1. The user can operate the operation lever70by pulling down the operation arm73frontward with the thumb of the left hand while gripping the knob44with the left hand. The transmission lever90is located between the operation lever70and the movable cover60. The operation lever70has a shorter length from a rotation center70ain the radial direction than an operation lever70used directly for opening the movable cover60. Thus, the operation part84of the operation lever70is displaced by a smaller amount.

The operation lever70includes an output arm77. The output arm77is mounted onto the rotational shaft71inside the stationary cover50. The operation lever70rotates the transmission lever90with the output arm77pushing the transmission lever90. The output arm77has a fitting hole78in its basal end. The fitting hole78receives the rotational shaft71. The cylindrical rotational shaft71has two flat portions79on its opposite side surfaces. The fitting hole78in the output arm77is shaped complementarily to the two flat portions79on the side surfaces of the rotational shaft71. The output arm77is thus nonrotatable relative to the rotational shaft71.

The output arm77is mounted onto an end of the rotational shaft71with a fixing screw80. The fixing screw80holds the output arm77onto the rotational shaft71via a washer81larger than the fitting hole78in the output arm77. The output arm77has a screw hole82in its distal end. The screw hole82receives a hexagon socket bolt83to fasten the output arm77. The hexagon socket bolt83includes a head with a cylindrical side surface that is smooth without irregularities. The operation lever70pushes the transmission lever90with the side surface of the hexagon socket bolt83. The operation lever70is thus highly slidable with the transmission lever90. The output arm77is shorter than the operation arm73. The operation lever70is thus operable with a smaller force. The output arm77extends in a direction substantially opposite to the operation arm73about the rotation center70a. However, the operation arm73can be mounted at any angles as appropriate using the serrations74.

Transmission Lever

As shown inFIG. 6, the transmission lever90includes an arm91. The arm91extends from a basal end of the transmission lever90and between the rotation center70aof the operation lever70and a rotation center90aof the transmission lever90. The operation lever70rotates the transmission lever90with the output arm77pushing the arm91. As shown inFIGS. 7 and 8, the arm91has a shaft hole92in its basal end. The shaft hole92receives a stepped screw93serving as a pivot shaft for the transmission lever90. The stepped screw93is screwed into a screw hole in the side wall53of the stationary cover50. The transmission lever90is supported on the stationary cover50with the stepped screw93through its shank94in a rotatable manner. The transmission lever90has the rotation center90alocated rearward from the rotation center70aof the operation lever70. This allows use of space rearward from the operation lever70.

The transmission lever90is urged in a direction in which the arm91is raised frontward by a tension spring95anchored to the side wall53of the stationary cover50(counterclockwise as viewed from the right of the portable cutting machine). The tension spring95has an end hooked in a hole96near the basal end of the arm91. This structure allows the transmission lever90to return to the initial position under the urging force from the tension spring95when the movable cover60is open to a certain degree and the operation lever70is left unoperated. The transmission lever90then pushes the operation lever70to return to the initial position (FIG. 4).

The arm91includes a front extension97and a downward extension98. The front extension97extends frontward from the rotation center90a. The downward extension98extends downward from a distal end of the front extension97. The operation lever70pushes the front face of the downward extension98to rotate the transmission lever90. The operation lever70thus continuously pushes the transmission lever90at a position farther from the rotation center90aof the transmission lever90, efficiently transmitting the power from the operation lever70to the transmission lever90.

As shown inFIGS. 2 and 6, the arm91is shaped to have a shorter distance from the rotation center90aof the transmission lever90to a contact between the arm91and the operation lever70in response to a higher degree of opening of the movable cover60. The operation lever70transmits power efficiently to the transmission lever90at the beginning of the rotation.

The transmission lever90has a rotation angle smaller than the rotation angle of the operation lever70when the movable cover60is to be open. The operation part is thus operable with a smaller force. This can be explained by the theory in power transmission that the product of the number of rotations (rotational speed) and the torque remains the same for the driver and the follower. When the follower has a smaller number of rotations than the driver, the follower has larger torque. For example, the operation lever70as the driver has a rotation angle of about 53 degrees, and the transmission lever90as the follower has a rotation angle of about 35 degrees. In this case, the transmission lever90has the number of rotations about 0.66 times (35 divided by 53) the number of rotations of the operation lever70, and thus has the torque about 1.51 times (53 divided by 35) the torque of the operation lever70. The operation lever70and the transmission lever90rotate in the same direction as the movable cover60when the movable cover60is to be open. Thus, the operation lever70can be moved in the direction intuitively with higher operability.

The transmission lever90rotated by the operation lever70pushes the movable cover60with a distal end of the downward extension98of the arm91to open the movable cover60. More specifically, as shown inFIG. 2, the movable cover60has the side wall63substantially semicircular and having two edges extending radially. One edge64faces upward when the movable cover60is at the closed position. The transmission lever90pushes the edge64, which faces upward, downward to open the movable cover60. The arm91includes the front extension97and the downward extension98. The arm91can thus avoid interfering with the rotation center (e.g., spindle) of the movable cover60when the transmission lever90moves, and can effectively push the movable cover60farther.

As shown inFIGS. 7 and 8, the transmission lever90includes a slider99. The slider99slides on the movable cover60while the transmission lever90is pushing the movable cover60. The slider99extends from the distal end of the downward extension98toward the saw blade. The slider99is formed from a synthetic resin, such as a polyacetal resin. The transmission lever90may be formed from a metal, such as an iron-based material, excluding the slider99. The transmission lever90is thus highly slidable on the movable cover60. The movable cover60may eliminate a modification of, for example, forming the edge64from a different material. In this design, the slidability is maintained in opening the movable cover60with the workpiece W in contact with the movable cover60. In another embodiment, the slider99may be coated with a synthetic resin (not shown) on its surface.

As shown inFIGS. 2 and 6, the contact between the movable cover60and the transmission lever90shifts rearward in response to a higher degree of opening of the movable cover60. The transmission lever90pushing the movable cover60thus does not protrude downward from the base in response to the opening of the movable cover60. The movable cover60has a shorter distance from the rotation center of the movable cover60to the contact between the movable cover60and the transmission lever90in response to a higher degree of opening of the movable cover60. The transmission lever90transmits power efficiently to the movable cover60at the beginning of the rotation.

As shown inFIG. 2, the transmission lever90is out of contact with the movable cover60when the movable cover60is at the closed position. The movable cover60may thus be at the closed position independent of the movable area of the transmission lever90. This reduces manufacturing variations for the closed position.

In another embodiment shown inFIGS. 9 and 10, the operation lever70may include a rolling member, such as a needle bearing, in place of the hexagon socket bolt83described above. The output arm77has a small hole in its basal end. A support shaft100is fitted into the small hole and is fixed. A needle bearing101is fitted onto the protruding portion of the support shaft. As the operation lever70pushes the transmission lever90, the needle bearing rolls over the transmission lever90. This improves slidability between the operation lever70and the transmission lever90.

Although the embodiments of the prevent invention are described above specifically, the invention is not limited to these embodiments. The embodiments may be variously substituted, modified, or altered by those skilled in the art without departing from the scope of the invention.

REFERENCE SIGNS LIST