CA1059011A

CA1059011A - Full position safety brake for portable chain saw

Info

Publication number: CA1059011A
Application number: CA274,015A
Authority: CA
Inventors: Sidney Hirschkoff
Original assignee: Black and Decker Inc
Current assignee: Black and Decker Inc
Priority date: 1976-04-19
Filing date: 1977-03-15
Publication date: 1979-07-24
Also published as: DE2716448A1; SE7704421L; SE434135C; DE2716448C2; SE434135B

Abstract

ABSTRACT OF THE DISCLOSURE

A hand portable chain saw with a movable safety bar for actuating a chain brake has a bracket and a lineally-acting spring which together provide a detent for holding the safety bar in the nonbraking operating position, but yet accelerate the braking movement of the safety bar upon disengagement from the detent.
The carrying handle for a portable chain saw encircles the top and both sides of the saw housing to enhance both oper-ator safety and convenience. The brake-actuating safety bar on the saw has a similar wrap-around contour to ensure engagement by the operator in the event of untoward movement of the saw for essentially any sawing position.

Description

lOS90~1 BACKGROUND OF THE INVENTION
This invention relates to handling and safety improve-ments in a hand portable chain saw. In particular, it provides an improved mechanism for braking the saw chain in the event of untoward movement of the saw, including in particular the hazardous kickback to which chain saws are subject. The inven-tion also provides improvements in both the carrying handle of the saw and in the safety bar which is located forward of the handle and initiates the braking operation.
It is known that hand portable chain saws are subject to a hazardous kickback motion during operation, and that a chain brake can be provided to reduce the risk of operator injury in the event of a kickback or other untoward saw movement. See for example U.S. Patents Nos. 3,776,331 of Gustafsson; 3,934,345 of Hirschkoff; and 3,937,306 of Naslund et al; and see also the February 1976 issue of Chain Saw Age for a state-of-the-art view of these aspects of chain saws.
However, some prior safety brake mechanisms do not pro-vide protection for all operating positions of the saw. Others are relatively complex in construction and/or operation, such as employing multiple-step release and braking action. Prior saws also have not provided all-position handle structures with equally-accessible chain brake actuation.
Accordingly, it is an object of this invention to pro vide improved handle and chain braking structures for hand port-able chain saws.
A more specific object is to provide a chain saw having both a carrying handle and a safety bar which are readily access-ible during operation of the saw in multiple orientations.
Another object of the invention is to provide a single-action chain brake which operates with a rotatable safety bar and which is located spaced from the rotation axis of the bar.

- 1 - ~

lOS901~

It is also an object of the invention to provide a chain brake employing a lineally-acting resilient element, such as a coil spring, which both holds the brake in disengagement, and alternatively applies braking force upon brake actuation.
Other objects of the invention will in part be obvious and will in part appear hereinafter.
GENERAL DESCRIPTION OF THE INVENTION
A hand portable chain saw embodying features of the invention has a carry handle, with which the operator supports most if not all the saw weight during use, which extends fully in wrap-around fashion about the top and the two sides of the saw housing. This handle is in addition to the control handle conventionally located at the rear of the saw opposite the chain-carrying arm, and which is fitted with the throttle and on-off controls. The wrap-around configuration of the carry handle provides ready access to the operator from both above and at least one side of the saw for any upright or sideways orientation of the saw, i.e. without regard to whether the saw is oriented for cutting vertically or horizontally to the right or to the left.
Located forward of the wrap-around housing-encircling drive handle, and in the path of the operator's hand, wrist, or arm in the event of kickback or other untoward movement of the saw, is a safety bar which has a similar housing-encircling wrap-around configuration. The safety bar is mounted to the housing, by means of rotatable connection at the ends of the bar, for a swinging movement about an axis located adjacent the lower face of the housing. This remote location of the rotation axis endows the safety bar with maximal sensitivity for deflection to actuate the brake mechanism.
The wrap-around handle configuration facilitates orient-ating the saw as appropriate for the desired cut. Hence it 10590~1 dimishes restrictions on the orientations with which the operator can use the saw, and correspondingly minimizes the likelihood that the operator will use the saw with an awkward, off-balance or otherwise insecure posture. The wrap-around safety bar with its extremely-located axis of rotation provides automatic chain braking for any such orientation of the saw.
The combination of wrap-axound handle and safety bar structures thus enhances both the efficiency and the safety of the saw.
A further characterization of the invention is a brake control and actuating mechanism having a lineally-acting spring which both biases the safety bar to apply the braking force and applies a brake latching detent to the safety bar. The brake employs the known arrangement in which a braking member is linked to the safety bar for brake engagement and, alterna-tively, disengagement. These known brakes also have a mechan-ism for holding the safety bar in the operating, i.e. brake-disengaging, position. However, a characteristic of a saw embodying the present invention is a coil spring or equivalent resilient element having substantially lineal action. When the safety bar is in the brake-disengaging position, the spring presses a detent against the safety bar. This action holds the safety bar cocked in an operating condition where the brake is released from the cutting chain. When the safety bar is disengaged from the detent, the same spring assumes the oppo-site role and thrusts the safety bar into the brake-engaging position.
This control and actuating mechanism of the invention is advantageously used with the wrap-around safety bar which the invention provides. This is because the remote location of the pivotal mounting of the wrap-around safety bar to the housing results in essentially lineal motion of the safety bar at the point where the brake-controlling mechanism advantage-lOS9011 ously is applied. Further, the spacings between the severalrotation axes and operating points of the safety bar and the control mechanism provide positive mechanical operation.
Hence, a saw combining the features of the invention provides a rapid, essentially snap-like, single-action braking which the operator automatically initiates when using the saw in essentially any orientation. The force of the hand against the safety bar plus the force of the spring causes a faster application of the brake and since the force of the hand is additive to the force of the spring, the stopping time of the chain is greatly shortened.
STATEMENT OF T~E INVENTION
The invention as claimed herein is a hand portable chain saw having a housing, a sawing chain mounted on an arm extending forward from the housing, motive means coupled for driving the sawing chain, a safety bar rotatable relative to the housing between a braking position and an operating position, and brake means coupled with the safety bar for brakingly engaging the motive means for stopping the sawing chain and alternatively for release from the motive means, and characterized by the improvement comprising detent-engaging means mounted for movement with the safety bar along a first direction between the brakiny and the operating positions thereof, first arm means extending longitudinal to the first direction and rotatably mounted for rotation re-lative to the housing about an axis different from the rota-tion axis of the safety bar, and having detent means for releasable latching engagement with the engaging means when the safety bar is in the operating position, and lineally-acting spring means engaged with the first arm means and withthe safety bar for applying a resilient force for urging the arm means rotatably into the latching engagement with the ~0590~
engaging means, and for urging the safety bar from the operating position into the braking position.
The chain saw may have the further improvement wherein the safety bar comprises a U-shaped barrier, the side portions and bottom portion of which extend respectively about the sides and top of the housing, and which is rotatably mounted at the end of each side portion to the housing adjacent a lowermost location on the housing.
The chain saw may have the further improvement comprising a detent bracket rotatably mounted to the housing and forming the first arm means and further providing a second arm extend-ing transversely to the first direction, and wherein the spring means is engaged between the second arm and the safety bar.
The~chain saw may have the further improvement wherein the spring means is located spaced from the rotatable mounting of the safety bar in the direction toward the top of the housing, and the detent bracket is rotatably mounted to the housing at a location intermediate the rotatable mounting of the safety bar and the location of the spring means.
The chain saw may have the further improvement comprising first shaft means mounting the safety bar to the housing for rotation about a first axis, and second shaft means mounting the detent member for rotation about a second axis parallel to the first axis. A further improvement may be wherein the first shaft means locates the first axis adjacent a lowermost location on the housing, and the second shaft means locates the second axis spaced, along a second direction transverse to the first direction, by a first distance toward the top of the housing from the first axis. The spring means may be engaged between the safety bar and the first arm means at a location spaced along the second direction by a distanGe greater than the first distance. The safety bar means may have a wrap-~OS90~1 ' around configuration extending about the top and sides of the housing and may extend continuously along the wrap-around configuration between a pair of end portions, and the first shaft means may engage the end portions for rotatably mounting the safety bar means.
The chain saw may have the further improvement wherein the spring means is engaged between the safety bar and the first arm means to constantly bias the safety bar forward to the braking position, and to impose yieldable latching force on the first arm means to resist forward movement of the safety bar and thereby prevent inadvertent brake engagement.
The chain saw may have the further improvement wherein the detent means is movable with the first arm means between a holding position for restraining movement of the safety bar means along the first direction and a release position allowing forward movement of the safety bar means, the lineally-acting spring means is arranged to bias the detent means into the holding position for imposing a yieldable latching force on the safety bar to resist forward movement of the safety bar and thereby to prevent inadvertent brake activation, and the detent means is movable to the release position against the bias of the spring means in response to forward movement o~ the safety bar. The spring means and the detent means may be arranged for increasing the bias of the spring means on the safety bar upon movement of the detent means from the holding position to the release position.
The chain saw may have a housing with top, bottom and sides and a carrying handle; a safety bar mounted on the housing for swinging movement between the operating position and the braking position; and a chain brake coupled with the safety bar for brakingly engaging the motive means to stop the chain and alternatively for release from the motive means; characterized by the further improvement wherein the carrying handle comprises a housing-encircling wrap-around hahdle extending about the top and sides of the housing, and the safety bar comprises a housing-encircling wrap-around barrier disposed forward of the carrying handle and extending at least sub-stantially coextensively with the handle about the top and sides of the housing. The chain saw may also include shaft means mounting the safety bar to the housing adjacent the bottom thereof, and spring-mounting means on the safety bar and on the housing and disposing the spring means for applying the resilient force to the safety bar at a distance from the mounting thereof such that the span of the safety bar along such distance provides a moment arm for the force of the spring.
The invention accordingly comprises the features of çonstruction, combinations of elements, and arrangements of parts exemplified in the embodiment hereinafter set forth, and the scQpe of the invention is indicated in the claims.
BRIEF DESCRIPTION OF DRAWINGS
.
For a further understanding of the nature and objects of the invention, reference should be had to the following detailed description and the accompanying drawings, in which:
FIGURE 1 shows a hand portable chain saw embodying the invention;
FIGURE 2 is a side elevation view of the saw of FIGURE
1 showing both the operating and the braking positions of the safety bar;
FIGURE 3 is a front elevation view of the saw of FIGURE
l;
FIGURE 4 is a partial sectional view of the saw as shown in FIGURE 3 and detailing the brake mechanism; and FIGURE 5 and 6 are fragmentary elevation views, of the side opposite to that shown in FIGURE 2 and partly bro~en a~7ay, showing the brake in the operating and the braking condi-tions,respectmvely.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS
A hand portable chain saw 10 embodying the invention as shown in FIGURES 1, 2 and 3 has a housing 12 and a sawing chain 14 trained over a forwardly projecting support arm 16.
The housing contains the saw drive mechanism, conventionally an internal combustion engine coupled by way of a power trans-mission and clutch to the sawing chain. A rewind starter 18 is accessible on one side of the housing 12 and a chain brake 20, described in further detail below, is located on the other side of the housing. At the rear of the housing is a control handle 22 fitted with a throttle trigger 24 and an on-off switch 26.
A carry handle 28 encircles the housing top 12a and two sides 12b and 12c roughly midway along the housing length so that the saw weight is approximately balanced at the handle.
The operator supports the weight of the saw from the handle 28, and hence this weight balance is important for operator conven-ience and safety. The operator uses the control handle 22 to stabilize the saw, and to control the chain operation and speed by means of the throttle trigger 24 and the switch 26.
The carry handle 28 is rigidly fixed to the housing 12.
In the illustrated embodiment the handle ends are secured with-in a tubular mount 30 which projects on the housing below the bottom panel 12d; this tubular projection provides a raised base on which to rest the saw. The carry handle 28 has a con-tinuous, housing-encircling wrap-around configuration between the angled end portions 28a, by which it is mounted. It thus has an overall U-shape between these end portions and formed with side portions 28c and 28d that form legs of the U and a top portion 28e that forms the base of the U-shape. A support stud 32 extends from the handle 28 adjacent the juncture of the top portion 28e with the side portion 28d, and is fastened at 1059(1 11 its other end to the housing, illustratively at the corner where the top and side meet. Thus in the preferred embodiment illustrated, the carry handle 28 has three points of attachment to the saw housing for secure rigidity throughout the entire wrap-around extent of the handle. Further, there are no free ends or other protrusions that could snag clothing or other-wise be hazardous.
FIGURES 1 and 3 show that this handle construction fully encircles the housing top and sides. The drive handle accordingly is accessible from both above and at least one side of the saw for the many orientations in which the saw is likely to be used. Further, except for the attachments to the housing, the entire span of the drive handle is spaced outwardly from the housing openly to receive the operator's hand between the handle and the housing for secure gripping of the handle.
With further reference to FIGURES 1, 2 and 3, the saw 10 has a safety bar 34 that actuates the chain brake 20 when displaced from an operating position 36a, FIGURE 2, to a braking position 36b. The safety bar follows the full wrap-around con-tour of the carry handle 28 to be interposed between the opera-tor's hand on the carry handle and forward portions of the saw for all cutting orientations. The safety bar 34 thus has a continuous structure which encircles the top and both sides of the saw housing 12, and has an overall U-shape with leg portions 34a and 34b and a base portion 34c.
The safety bar is located on the housing 12 spaced forward of the drive handle and aligned generally parallel to it when in the operating position 36a. The bar is mounted for swinging rotation relative to the housing about an axis 38 by means of shafts 37 and 39 fixed on the ends of the bar and rotatably seated to the housing at locations lowermost on the housing sides.

~059011 This structure interposes the safety bar in the path of the operator's hand, wrist or arm in the event the saw kicks back or in case of other potentially hazardous untoward move-ment of the saw. The operator's body accordingly will engage the safety bar and thereby displace it from the operating posi-tion 36a. As will now be described, this displacement of the safety bar actuates the chain brake to stop the chain essent-ially instantaneously.
With reference to FIGURES 4, 5 and 6, the chain brake 20 (FIGURE 2) applies braking force to a brake drum 40 that the saw drive mechanism rotates upon driving the saw chain.
Typically, within the housing, the chain is trained on a sproc-ket wheel which is mechanically coupled to the shaft 42 on which the brake drum rotates. In one construction, the brake drum 40 rotates with a driven member of the clutch that drives the chain.
The brake employs a flexible brake band 44 which has one end 44a secured to the housing, illustratively by seating a loop at that end of the band within a cavity 46 recessing the housing. The other end 44b of the brake band is secured to the safety bar 34, for example, by seating a loop at that end on a pin 48 extending from the safety bar. The brake band extends from the pin 48 along a path extending length-wise of the saw and then around the periphery of the brake drum 40. Adjacent the fixed end 44a, the brake band passes over a guide surface provided by a housing pin 50 and thence to the housing anchor-age in cavity 46. The brake band thus encircles nearly the full periphery of the brake drum 40.
The pin 48 is located on the safety bar spaced from the rotation axis 38 by a sufficient distance such that it moves along an essentially straight path directed along the saw length when the safety bar moves between the two positions shown in 10590~1 FIGURE 2.
This movement of the pin 48 operates the brake, as FIGURES 5 and 6 illustrate. In particular, when the safety bar 34 is in the non-braking, operating position of FIGURE 5, the brake band 44 loosely circles the drum 40 and hence applies no brake force to it. The brake accordingly does not interfere with free rotation of the drum 40 and correspondingly with the drive motion applied to the chain. However, upon movement of the safety bar to the braking position, FIGURE 6, the pin 48 moves forward with the safety bar and pulls the brake band taut around the brake drum. Frictional engagement between the drum and the brake band, either of which can carry brake linings according to conventional practice, arrests the rotation of the brake drum 40 and thereby stops the sawing chain.
A detent and thrust mechanism, formed by a detent bracket 52 and a lineally-acting spring 54, latches the safety bar in the operating position but yet drives it into the braking position when the safety bar is unlatched. As FIGURE 4 shows, the bracket and the spring are nested between the safety bar and one side of the housing. The bracket 52 forms two substan-tially orthogonal arms, one a detent arm 56 which extends along the length of the saw and the other an upstanding lever arm 58.
The arm 56 has an upwardly-facing detent step 56a dimension to latchingly receive and retain the pin 48, as FIGURE 5 shows, when the safety bar is retracted to the operating position.
The bracket 52 is mounted -- between the two arms which it forms -- to the housing on a stem 60 for rotation about an axis parallel to the axis 38 of safety bar rotation. The two rota-tion axes are spaced apart along the safety bar, i.e. in the direction transverse to the saw length. The spring 54, prefer-ably a coil spring as shown, is compressively seated between the arm 58 and a rearwardly facing platform surface 34d on the ~OSS~011 safety bar. Each element 58 and 34 illustratively includes a stud which fits within the open center of the spring to retain it from accidental dislodgement. Further, the studs are ar-ranged to abut one another in the event the safety bar is ro-tated too far counterclockwise; they thus prevent over-compres-sion of the spring 54. Clockwise rotation of the safety bar is limited by the length of the brake band 44, as FIGURE 6 shows.
(Directions of rotation are termed clockwise and counterclock-wise with reference to FIGURES 2, 5 and 6.) With the foregoing mounting by way of the detent brack-et 52, the spring 54 is oriented along the saw length and is compressed more when the safety bar is in the operating position (FIGURE 5) than when in the braking position (FIGURE 6). This additional compression stores kinetic energy in the spring.
Hence, when in the operating position, the spring increasingly pushes the bracket 52 counterclockwise about the stem 60, and thereby resiliently presses the detent shoulder 56a in front of the pin 48, to latch the safety bar in the operating position.
However, when the safety bar is struck or otherwise pressed in the forward direction, it rotates clockwise about the axis 38. This motion carries the pin 48 forward. The pin accordingly cams past the detent shoulder 56a, thereby rotating the bracket 52 and hence the arm 58, clockwise. This in turn maintains initial compression in the spring 54. The force of the compressed spring pushes against the safety bar and thereby thrusts it and the pin 48 forward to engage the brake band against the drum 40.
The brake thereafter is released simply by swinging the safety bar backwards, i.e. counterclockwise. This motion latchingly re-engages the pin 48 in the detent of arm 56 and again compresses the spring 54 so that it biases the detent bracket 52 to hold the brake cocked in the operating condition.

~059011 The foregoing construction of the control and actuating mechanism provides a moment arm in the length of the safety bar between the axis 38 and the spring 54, i.e. and the spring-engaging shoulder 34d. As illustrated, this moment arm pre-ferably is longer than the second moment arm provided by the length of safety bar between the axis 38 and the pin 48. It is the former moment arm through which the spring acts to rotate the safety arm, and the latter moment arm moves the pin 48 to apply the brake.
NON-OBVIOUSNESS AND SCOPE OF INVENTION
AND SUMMARY OF ADVANTAGES
The present invention is characterized by means, operation and results which are wholly different from those of the prior art. These differences, coupled with the failure of the prior art to suggest the present invention as well as that of the aforesaid parent application Serial No. 515,047, evidence the non-obviousness of the invention of the present application and applicant's parent case.
For example, structures disclosed and claimed in prior patents such as Gustafsson 3,776,331 (1973) and Naslund et al 3,937,306 (1976) are predicated on the use of separate springs for operating brake band biasing means and latching means. They do not contemplate either the unique linear or torsional embodi-ments of the detent-biasing arrangements of this application and its parent case.
Moreover, prior art devices as featured in the Gustafsson patent involve the use of a rigid locking mechanism with an associated trigger releasP device which entail two-step operation and require a recocking of lock components before relatching can be effected. In the first Gustafsson step, the locking mechanism is released. In the second Gustafsson step, which is sequentially independent of the release step, setting ~059011 of the brake band is commenced.
The different structure of the present invention and of the aforesaid parent case, in relation to prior proposals such as Gustafsson and Naslund et al, entails the use of a unique single spring arrangement -- as opposed to multiple springs --for performing both brake band and safety bar biasing and safe-ty bar detenting in a novel and advantageous manner. Moreover, in contrast with Gustafsson, this different structure enables movement of the safety bar serving, in one-step, concurrently to release the detent and initiate the setting of the brake band. The rigid locking mechanism of Gustafsson is displaced entirely in favor of a yieldable detent approach for yieldably securing the safety bar.
A different mode of operation of the present invention, as well as the aforesaid parent case, in relation to prior art such as Gustafsson, entails the concurrence of safety bar re-lease and brake setting action in contrast with the sequential and independent unlocking and brake band setting actions of Gustafsson. In addition, instead of moving a pawl out of en-gagement with a brake as contemplated by Gustafsson, the inven-tions of this application and its parent case entail the use of a detent which remains engaged so as to avoid the need for a recocking of trigger elements.
A different result achieved by the present invention, in contrast with Gustafsson, entails the initiation of brake setting action concurrent with the initiation of the safety bar movement, in lieu of the unlocking action of Gustafsson which intervenes before setting of the brake band can commence.
And, as noted, the yieldable detent approach of the present invention and that of its parent case wholly avoids the recocking concept of Gustafsson which is necessary to reposition the elements of a trigger-type locking mechanism before relatch-~OS90~1 ing of the safety bar can occur.
As to the wrap-around handle aspect of the present in-vention and that of the parent case, there simply is no sug-gestion to be found in prior art such as Gustafsson and Naslund et al.
The handle and brake of the invention will now be understood to provide improvements in operation, control and safety for a hand portable chain saw. The wrap-around carry handle mounts to the housing at a lowermost location and other-wise encircles the housing for ready gripping by the operatorfrom essentially any direction. The saw safety bar encircles the housing in a like manner so that any untoward movement will automatically cause the operator to strike the bar and thereby trip the chain brake.
A single bracket and single spring element coupled between the safety bar and the saw housing latch the safety bar in a normal standby position where the saw operates free of the brake. However, dislodgement of the safety bar from this posi-tion causes the bracket-spring combination to drive the safety bar -- aided by whatever force the operator's thrust applies --to the braking position. A single movement of the spring-biased bracket produces both the release and the brake-applying thrust.
It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained. Since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended to cover all of the generic and specific features 10590~1 of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

16 ~

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A hand portable chain saw having a housing, a sawing chain mounted on an arm extending forward from the housing, motive means coupled for driving the sawing chain, a safety bar rotatable relative to the housing between a braking position and an operating position, and brake means coupled with the safety bar for brakingly engaging the motive means for stopping the sawing chain and alternatively for release from the motive means, and characterized by the improvement com-prising a. detent-engaging means mounted for movement with the safety bar along a first direction between said braking and said operating positions thereof, b. first arm means extending longitudinal to said first direction and rotatably mounted for rotation relative to the housing about an axis different form the rotation axis of the safety bar, and having detent means for releasable latching engagement with said engaging means when the safety bar is in said operating position, and c. lineally-acting spring means engaged with said first arm means and with the safety bar for applying a resilient force for urging said arm means rotatably into said latching engagement with said engaging means, and for urging the safety bar from said operating position into said braking position.

2. A hand portable chain saw according to claim 1, naving the further improvement wherein said safety bar com-prises a U-shaped barrier, the side portions and bottom portion of which extend respectively about the sides and top of the hou-sing, and which is rotatably mounted at the end of each side por-tion to the housing adjacent a lowermost location on the housing.

3. A hand portable chain saw according to claim 1 or claim 2, having the further improvement comprising a. a detent bracket rotatably mounted to the housing and forming said first arm means and further providing a second arm extending trans-versely to said first direction, and b. wherein said spring means is engaged between said second arm and the safety bar.

4. A hand portable chain saw according to claim 1 having the further improvement a. comprising a detent bracket rotatably mounted to the housing and forming said first arm means and further providing a second arm extending transversely to said first direction, b. wherein said spring means is engaged between said second arm and the safety bar, and is lo-cated spaced from said rotatable mounting of said safety bar in the direction toward the top of the housing, and c. wherein said detent bracket is rotatably mounted to the housing at a location intermediate said rotatable mounting of said safety bar and the location of said spring means.

5. A hand portable chain saw according to claim 1 having the further improvement comprising a. first shaft means mounting said safety bar to the housing for rotation about a first axis, and b. second shaft means mounting said detent member for rotation about a second axis parallel to said first axis.

6. A hand portable chain saw according to claim 5, having the further improvement wherein a. said first shaft means locates said first axis adjacent a lowermost location on the housing, and b. said second shaft means locates said second axis spaced, along a second direction transverse to said first direction, by a first distance toward the top of the housing from said first axis.

7. A chain saw according to claim 6, having the further improvement wherein said spring means is engaged between said safety bar and said first arm means at a location spaced along said second direction by a distance greater than said first distance.

8. A hand portable chain saw according to claim 6, having the further improvement wherein a. said safety bar means has a wrap-around configuration extending about the top and sides of said housing and extends contin-uously along said wrap-around configuration between a pair of end portions, and b. said first shaft means engages said end portions for rotatably mounting said safety bar means.

9. A hand portable chain saw according to claim 1, having the further improvement wherein said spring means is engaged between said safety bar and said first arm means to constantly bias the safety bar forward to said braking position, and to impose yieldable latching force on the first arm means to resist forward movement of the safety bar and thereby pre-vent inadvertent brake engagement.

10. A chain saw according to claim 1, having the fur-ther improvement wherein a. said detent means is movable with said first arm means between a holding position for restraining movement of said safety bar means along said first direction and a release position allowing forward move-ment of said safety bar means, b. said lineally-acting spring means is arranged to bias said detent means into said holding position for imposing a yieldable latching force on said safety bar to resist forward movement of the safety bar and thereby to prevent inad-vertent brake activation, and c. said detent means is movable to said release position against the bias of said spring means in response to forward move-ment of said safety bar.

11. A chain saw according to claim 10, having the fur-ther improvement wherein said spring means and said detent means are arranged for increasing the bias of said spring means on said safety bar upon movement of said detent means from said holding position to said release position.

12. A hand portable chain saw according to claim 1 and having a housing with top, bottom and sides and a carrying handle;
a safety bar mounted on the housing for swinging movement between said operating position and said braking position; and a chain brake coupled with the safety bar for brakingly engaging the motive means to stop the chain and alternatively for release from the motive means;
characterized by the further improvement wherein a. said carrying handle comprises a housing-encircling wrap-around handle extending about the top and sides of the housing, and b. said safety bar comprises a housing-encircling wrap-around barrier disposed forward of said carrying handle and extend-ing at least substantially coextensively with said handle about the top and sides of the housing.

13. A hand portable chain saw according to claim 12, having the further improvement comprising a. shaft means mounting said safety bar to said housing adjacent the bottom thereof, and b. spring-mounting means on said safety bar and on said housing and disposing said spring means for applying said resilient force to said safety bar at a distance from said mounting thereof such that the span of said safety bar along such distance provides a moment arm for the force of said spring.