Guide Bar Adjustment For Chain Saw

Abstract

The tightness of the saw chain on the guide bar of a chain saw is adjustable by means of a tool-rotatable member which extends to the outside of the drive case cover and is connected through helical gears with an adjusting screw mounted in fixed location adjacent a rear end portion of the guide bar for rotation about an axis extending lengthwise of the guide bar. An internally threaded rider on the adjusting screw is interconnected with the guide bar so as to move the guide bar lengthwise when the rider is moved by rotation of the adjusting screw. The location of the rotatable member by which the adjusting screw can be rotated makes it possible to adjust the tightness of the chain on the guide bar conveniently and safely.

Description

FIELD OF INVENTION

The present invention relates to power driven chain saws having a saw chain running on a guide bar which extends forwardly from a chassis and particularly to convenient means for adjusting the tightness of the chain on the guide bar.

BACKGROUND OF INVENTION

A chain saw customarily has an elongated guide bar which is mounted on and extends forwardly from a power head or chassis including a motor. A cutting chain which runs on the guide bar is driven by engagement with a sprocket which is located at the rear end of the guide bar and is driven by the motor. In order for the saw to operate properly and safely the tightness of the saw chain on the guide bar needs to be adjusted so that the chain runs freely on the guide bar without excessive friction but is sufficiently tight so that it will not come off of the guide bar during operation of the saw. Adjustment is periodically required because of chain stretch caused by tension from cutting. Adjustment of the tightness of the cutting chain on the guide bar is effected by adjustably moving the guide bar in a lengthwise direction relative to the chassis and hence relative to the sprocket by which the chain is driven so as to vary the distance between the sprocket and the forward end of the guide bar. Heretofore, such adjustment has customarily been effected by means of an adjusting screw rotatably mounted on the chassis adjacent a rear end portion of the guide bar and having a follower or rider which is interconnected with the guide bar so that the rider and hence the guide bar can be moved in a direction longitudinal of the guide bar by rotation of the adjusting screw. One end of the adjusting screw is usually provided with a transverse slot to receive the bit of a screwdriver by which the screw can be turned to adjust the tightness of the chain. By reason of the location of the adjusting screw between a portion of the chassis and the guide bar, it has been necessary for an operator either to turn the saw around so that the guide bar is toward him or else reach over the guide bar in order to turn the adjusting screw by means of a screwdriver. This has made the adjustment of the tightness of the chain on the guide bar inconvenient and also somewhat hazardous since there is the possibility of the operator being injured by engagement with the sharp cutting chain.

SUMMARY OF INVENTION

It is an object of the present invention to provide for adjustment of the tightness of the cutting chain of a chain saw in a manner which is more convenient and safer than heretofore. In accordance with the invention, an adjusting screw for moving the guide bar of a chain saw in a lengthwise direction to adjust the tightness of the cutting chain is rotatably mounted not on the body of the chassis but inside a removable cover which encloses a rear end portion of the guide bar and the sprocket by which the chain is driven. Moreover, the adjusting screw is rotatable by means of a rotatable member which extends to the outside of the cover and is hence conveniently accessible to an operator. The rotatable member is operatively connected with the adjusting screw by means of an angle drive. By virtue of this arrangement, an operator can adjust the tightness of the chain without turning the saw around and without reaching over the guide bar. Hence, adjustment of the tightness of the chain is made both more convenient and safer.

The guide bar is customarily mounted on the chassis of a chain saw by means of two stud bolts which project laterally from the chassis and extend through an elongated longitudinal slot in a rear end portion of the guide bar. The same bolts may be used for securing in place a cover enclosing a rear end portion of the guide bar and the sprocket by which the cutting chain is driven. Nuts screwed onto the bolts are loosened so as to free the guide bar for lengthwise movement to adjust the tightness of the chain and after adjustment are tightened so as to clamp the guide bar securely in adjusted position while at the same time securing the cover. In accordance with the invention the rotatable member by which the adjusting screw is rotated to adjust the tightness of the chain is preferably located adjacent the nuts on the bolts by means of which the guide bar is mounted on the chassis. By reason of this location, an operator can loosen the nuts on the stud bolts, turn the rotatable member to move the guide bar in a lengthwise direction to adjust the tightness of the chain and then tighten the nuts to secure the guide bar in adjusted position without changing his position with respect to the chain saw. This makes the adjustment most convenient.

BRIEF DESCRIPTION OF DRAWINGS

The nature, objects and advantages of the invention will be more fully understood from the following description in conjunction with the accompanying drawings which illustrate by way of example a preferred embodiment of the invention.

IN THE DRAWINGS

FIG. 1 is a side view of a portion of a chain saw in accordance with the invention including a portion of the guide bar and cutting chain and a cover enclosing a rear end portion of the guide bar;

FIG. 2 is an inside view of the cover;

FIG. 3 is a partial cross section taken approximately on the line 3--3 in FIG. 1; and

FIG. 4 is a partial cross section taken at the location indicated by the line 4--4 in FIG. 2 but with the cover and guide bar assembled on the chassis of the chain saw.

DESCRIPTION OF PREFERRED EMBODIMENT

Means for adjusting the tension of a saw chain is shown by way of example in the drawings as applied to a chain saw having a power head or chassis 1. In accordance with conventional construction, the chassis includes a power unit, for example an electric motor or an internal combustion engine enclosed in a suitable housing and provided with customary handles, controls and other accessories. As such construction is well known, only a portion of the chassis housing is shown in the drawings. This includes a portion 1a provided on a side of the chassis for mounting a guide bar 2. The guide bar is mounted on the chassis by means of two stud bolts 3 which project laterally from the portion 1a of the chassis and extend through an elongated longitudinal slot in a rear end portion of the guide bar 2. The slot in the guide bar is of sufficient length to permit lengthwise movement of the guide bar relative to the chassis. As seen in FIG. 3, the guide bar 2 is provided in its periphery with a groove to receive inwardly projecting tangs of a cutting chain 4 which is thereby guided so as to run around the periphery of the guide bar. The chain is shown as comprising a plurality of links 4a connected by rivets 4b. Certain of the links are provided with cutting teeth 4c and depth gauges 4d. A rear end portion of the guide bar 1 with the chain thereon is enclosed by a drive case cover 5 which is mounted on the chassis by means of the stud bolts 3 which extend through holes suitably provided in the cover and are provided with nuts 6 which are screwed onto the bolts to hold the cover 5 and the guide bar 2 in place. A guard plate or shim 7 is sandwiched between the guide bar 2 and the mounting portion 1a of the chassis and a similar but reversed guard plate or shim 8 is sandwiched between the guide bar and the cover 5. At the rear end of the guide bar the chain runs over and is driven by a sprocket which in turn is driven by the power unit usually through a speed responsive clutch. As the sprocket and the means for driving it are well known, they are not shown in the drawings. The guard plates 7 and 8 serve to guide the cutting chain as it runs onto and off of the sprocket. As viewed in FIG. 1, the lower run of the chain 4 is moving toward the sprocket while the upper run of the chain is moving toward the outer end of the guide bar.

Adjustment of the tightness of the chain on the guide bar is effected by moving the guide bar in a lengthwise direction with respect to the chassis. As the sprocket is in a fixed location with respect to the chassis, movement of the guide bar forwardly (toward the right in FIG. 1) increases the distance between the sprocket and the forward end of the guide bar, thereby tightening the chain. Conversely, rearward movement of the guide bar with respect to the chassis loosens the chain. Longitudinal movement of the guide bar with respect to the chassis is effected by means of a threaded shaft 10 which is herein referred to as an adjusting screw. The shaft 10 is externally threaded except for cylindrical end portions 10a and 10b by means of which the shaft is mounted for rotation on the inside of the drive case cover 5. One end portion 10a is rotatably received in a cylindrical hole provided in an inwardly projecting portion 5a of the drive case cover while the other end portion 10b is rotatably held between a half bearing portion of the drive case cover and a complementary bearing portion of a gear cover 11 secured on the inside of the drive case cover by screws 12. In this manner, the adjusting screw 10 is rotatably mounted adjacent a rear end portion of the guide bar 2 below the slot receiving the mounting bolts 3. As seen in FIGS. 2 and 4, the adjusting screw 10 is located below the bolts 3 and extends approximately from one bolt to the other. The axis of the adjusting screw 10 is parallel to the plane of the guide bar and extends lengthwise of the guide bar so as to be parallel with the slot receiving the mounting bolts 3.

An internally threaded rider or follower nut 13 engages the threaded portion of the adjusting screw 10 so as to be moved longitudinally of the screw when the screw is rotated. The rider 13 is connected with the guide bar by means of a laterally projecting lug portion 13a of the rider extending into an opening 2a provided in the guide bar below the slot receiving the mounting bolts 3. A second like opening (not shown) is preferably provided at a corresponding location on the opposite side of the central slot for the mounting bolts so that the guide bar is reversible. The interengagement of the lug portion 13a of the rider 13 with the hole 2a in the guide bar provides a connection for transmitting axial movement of the rider 13 to the guide bar thereby moving it in a lengthwise direction relative to the chassis. At the same time, the lug 13a prevents rotation of the rider. Thus, by rotating the adjusting screw 10 in one direction, the guide bar 2 can be moved forwardly to tighten the chain while rotation of the adjusting screw 10 in the opposite direction moves the guide bar rearwardly to loosen the chain.

In accordance with the present invention, the adjusting screw 10 is reversibly rotatable by means of a rotatable adjusting member located in a position which is conveniently accessible to an operator. As the axis of the rotatable adjusting member is disposed at an angle to the axis of the adjusting screw 10, the two are interconnected by an angle gear drive. While a worm gear or other suitable angle gear drive might be used, it is preferred to use helical gears as illustrated by way of example in the drawings.

As illustrated in FIG. 3, the adjusting member comprises a rotatable member 15 having a larger cylindrical head portion 15a and a stem portion 15b of reduced diameter. The head portion 15a is rotatably received in an opening provided in a recessed portion 5b of the drive case cover 5 while the stem portion 15b is rotatably supported by an axially aligned hole in the gear cover 11. The member 15 is thereby supported for rotation about an axis which is perpendicular to the guide bar 2 and below the axis of the adjusting screw 10.

The rotatable adjusting member 15 is operatively connected with the adjusting screw 10 by means of a helical gear 16 fixed on the stem portion 15b of the member 15 and meshing with a helical gear 17 fixed on the end portion 10b of the adjusting screw 10. By reason of this gear connection the adjusting screw 10 can be rotated by turning the rotatable adjusting member 15.

The adjusting member 15 extends to the exterior of the drive case cover 5 and is provided with means whereby it can easily be rotated. As illustrated by way of example in FIG. 3, a transverse slot 15c is provided in the outer end of the adjusting member 15 to receive the bit of a screwdriver. Alternatively, the adjusting member 15 can be provided with a wrench head or an Allen head socket whereby it can readily be turned by means of a suitable tool.

In order to move the guide bar 2 longitudinally and thereby adjust the tightness of the chain, it is necessary first to loosen the nuts 6 on the mounting bolts 3 sufficiently to permit the guide bar to move. The guide bar is guided in its longitudinal movement by engagement of the spaced bolts 3 with the side edges of the central guide bar slot in which the bolts are received. When the nuts 6 have been suitably loosened the guide bar is then moved in the desired direction by rotating the adjusting member 15 by means of a screwdriver or other suitable tool. The nuts 6 are then tightened so as to clamp the guide bar in adjusted position. Since the adjusting member 15 is located near the nuts 6, it will be seen that the entire operation can conveniently be carried out by an operator without changing his position with respect to the chain saw. As illustrated particularly in FIGS. 1 and 3, the adjusting member 15 and the nuts 6 are located in the same recess 5b of the drive case cover 5 and are thereby protected. The location of the adjusting member 15 as well as the nuts 6 on the outside of the drive case cover provides for convenient and safe adjustment of the tightness of the saw chain. Moreover, since the adjusting screw 10 and the gear drive are removably mounted on the inside of the drive case cover which can readily be removed from the saw merely by removing the nuts 6, these parts are easily acceptable for cleaning, lubrication or inspection.

While a preferred embodiment of the invention has been illustrated by way of example in the drawings and is herein particularly described, it will be understood by those skilled in the art that the invention is in no way limited to the illustrated embodiment.

Claims

1. In a chain saw having a chassis, an elongated guide bar mounted on and extending forwardly from the chassis, a saw chain running on the guide bar and a cover enclosing a rear end portion of the guide bar; means for adjustable moving the guide bar in a lengthwise direction relative to the chassis to adjust the tightness of the chain on the guide bar, comprising an elongated adjusting screw, means rotatably mounting said adjusting screw in fixed location relative to the chassis adjacent a rear end portion of the guide bar and with its longitudinal axis extending lengthwise of the guide bar, an internally threaded rider on said screw in engagement with threads thereof and movable lengthwise of the screw by rotation of the screw, means interconnecting said rider and guide bar to move the guide bar in a lengthwise direction by said rider, a first gear fixed on and rotatable with said screw, a second gear meshing with said first gear and rotatable about an axis normal to the axis of said screw, and driving means fixed with said second gear and extending to the outside of said cover, said driving means having means accessible from outside said cover for rotating said driving means and thereby rotating said second gear, first gear and screw to move said rider and guide bar in a direction lengthwise of the guide bar to adjust the tightness of said

2. In a chain saw, guide bar adjusting means according to claim 1, in which

3. In a chain saw, guide bar adjusting means according to claim 1, in which said means for rotating said driving means comprises means at an outer end of said driving means to receive a tool for rotating said driving means.

4. In a chain saw, guide bar adjusting means according to claim 3, in which said cover has a recessed portion in which said drive means is located so that said drive means does not project beyond an outer surface of the

5. In a chain saw, guide bar adjusting means according to claim 1, in which said means rotatably mounting said adjusting screw comprises means for

6. In a chain saw, guide bar adjusting means according to claim 5, having means for removably securing said cover on said chassis, said securing means comprising stud bolts on said chassis extending through an elongated slot in said guide bar and through holes in said cover, and nuts screwed on said bolts to secure the cover in place and clamp a rear end portion of

7. In a chain saw, guide bar adjusting means according to claim 6, in which said driving means is located in the vicinity of said nuts so that said nuts and driving means are conveniently accessible in the same location.

8. In a chain saw having a chassis, an elongated guide bar mounted on and extending forwardly from the chassis, a saw chain running on the guide bar and means enclosing a rear end portion of the guide bar; means for adjustably moving the guide bar in a lengthwise direction to adjust the tightness of the chain on the guide bar, comprising an elongated adjusting screw, means rotatably mounting said adjusting screw in fixed location relative to the chassis adjacent a rear end portion of the guide bar and with its lontitudinal axis extending lengthwise of the guide bar, an internally threaded rider on said screw in engagement with threads thereof and movable lengthwise of the screw by rotation of the screw, means interconnecting said rider and guide bar to move the guide bar in a lengthwise direction by said rider, means for releasably clamping said guide bar in fixed adjusted position on the chassis, drive means for rotating said adjusting screw, means rotatably mounting said drive means in a location conveniently accessible to an operator with its axis of rotation at an angle to the axis of rotation of said screw and angle drive connecting means connecting said drive means with said screw, whereby an operator after releasing said clamping means can adjust the tightness of the chain on the guide bar by rotating said drive means, the rotation of said drive means being transmitted through said angle drive connecting means to said screw to rotate said screw and thereby move said rider and guide bar in a direction lengthwise of the guide bar, whereupon said clamping means is actuated to clamp the guide bar fixedly in adjusted

9. In a chain saw, guide bar adjusting means according to claim 8, in which said clamping means and said drive means are located adjacent one another so that both are conveniently operable by an operator from a single position.