referring to fig1 , a chain saw 10 pivotally mounted for rotation within a shielding saw casing or saw box portion 12 of a dongle head 14 suspended from the main boom 16 and jib boom 18 of a forest harvester 20 is shown cutting through the trunk of a felled tree 22 . the arrows 24 indicate possible directions of travel for chain shot if the cutting chain 26 were to break . prior to my present invention , the accepted way in the timber harvesting industry to contain chain shot has been to install on a forest harvester chain saw a chain shot guard 28 that partially surrounds a proximal end portion of the chain saw . it was intended that , should pieces of the cutting chain 30 break off , the chain shot would be captured within the convex , apposed surface of the chain shot guard . it was also common to further include a chain catcher 32 , as depicted in fig2 , as an axial , cylindrical stub extension ( or bobbin - shaped , as in fig3 and 4 ) of the drive shaft of the drive shaft of the hydraulic motor assembly 34 , with the intent that , if the cutting chain 30 were to become detached from the chain guide bar 36 of the chain saw ( see , for example , fig3 ), the detached cutting chain would wrap itself around the chain catcher 32 and thereby be captured . sometimes , however , the detached cutting chain 30 broke up into chain shot instead . the present invention dispenses with the chain catcher 32 ( fig2 , 3 and 4 ) and chain shot guard 28 ( fig2 ) of the prior art . to illustrate how one installs a first embodiment of my chain containment device 100 on a harvester chain saw 10 , selected component parts of a disassembled forest harvester chain saw of the prior art ( e . g ., a keto 800 phd processor ) are depicted in fig6 . illustrated in fig6 are the chain bar mount 38 , which comprises a rectilinear , distal base portion 38 d joined to , and coplanar with it , a proximal ring portion 38 p ; a proximal portion 36 p of the chain guide bar 36 disposed adjacent to an exterior surface 38 e of the chain bar mount 38 ; a drive sprocket 40 disposed at an exterior side 40 of the proximal ring portion 38 p of the chain bar mount and aligned for rotation about the hydraulic motor drive shaft axis ( a - a ); and a closed - loop , cutting chain 30 looped around the chain guide bar and the drive sprocket . the drive sprocket 42 , which attaches to the drive shaft 44 of the hydraulic motor assembly ′ 34 , has a first set of radially - directed teeth 42 a and , disposed on an opposite side of the sprocket , a coaxial second set of radially - directed teeth 42 b , such that , after excessive wear on the first set of teeth , the sprocket can be removed from the drive shaft , inverted , reattached to the drive shaft , and the second set of teeth can be used thereafter to drive the cutting chain 30 . the top 36 t , distal end 36 d , and bottom 36 b edges of the chain guide bar 36 has a continuous groove g , and , when the chain saw is operating , the cutting chain 30 moves through that groove . in fig7 , the cutting chain 30 has been installed on the disassembled chain saw 10 and a saw chain tensioner 46 has been positioned at the exterior surface 40 of the bar mount 38 and distally with respect to the drive sprocket 42 . the cutting chain 30 is looped around whichever of the two sets of sprocket teeth 42 a , 42 b , is currently flipped toward the interior side of the sprocket 42 , which , in the case of fig6 - 9 happens to be the set that has been designated 42 a , and that currently interiorly - disposed set of sprocket teeth lies within the plane of the chain guide bar 36 . thus , as it rotates around the chain guide bar 36 and the drive sprocket 42 , the cutting chain 30 remains within a plane that contains the chain guide bar ( whereas , the unused set of sprocket teeth 42 b lies outside of , and exterior to , said plane ). the proper positioning of the chain tensioner 46 is aided by a locating lug 48 that extends upward from an exterior side of the base portion of the bar mount and abuts a distal end 46 d of the chain tensioner as well as by a plurality of bores 49 in the tensioner for threaded fasteners 60 that align in registry with corresponding threaded bores in the bar mount 38 when the chain saw 10 is reassembled . the chain tensioner 36 includes a chain tension adjustment screw 46 s ( e . g ., allen screw ; fig1 ) within a longitudinal bore ( not shown ) that extends through the chain tensioner from the distal end 36 d thereof to a longitudinally slotted , proximal end portion 46 p thereof where it threads into a mating , threaded bore of a tensioner member ( not shown ) that is slidable within the slot and which attaches to a proximal end portion of the chain guide bar 36 , such that rotation of the screw 46 s permits adjustment of the tension in the cutting chain 30 . the present invention comprises deflector means , denoted generally by the numeral 50 , and chain catcher means , denoted generally by the numeral 52 . the purpose of the deflector means 50 is to deflect , during operation of the chain saw 10 , a detached or broken cutting chain 30 exteriorly away from the drive sprocket 42 , thereby preventing the drive sprocket from imparting additional kinetic energy to the cutting chain . in the first embodiment 100 , the deflector means 50 is disposed below the saw chain tensioner 46 and below the bottom edge 36 b of the chain guide bar 36 , such that the entrance surface s at a proximal end of the defector means is slightly interior ( e . g ., 1 cm to 3 cm ) to a plane that contains the interior surface of the chain guide bar . the deflector means 50 includes ramp means 54 having an exterior surface ( s to s ′) that extends proximally and exteriorly at an oblique angle with respect to the plane that contains the exterior surface 36 e of the chain guide bar 36 and thus actually crosses over the chain guide bar 36 , and means 56 for attaching the ramp means to the chain saw 10 . in the first embodiment 100 , the ramp means 54 comprises a flat , first face plate 102 and a semiannular arm 106 attached to an upper , proximal end 104 of the first face plate . the first face plate 102 is apertured ( openings 49 ′), shaped and dimensioned for attachment by threaded fasteners 60 to an exterior surface 46 e of the saw chain tensioner 46 , which fasteners extend through the above - described openings 49 in the chain tensioner . the ramp means 54 further includes a semiannular arm 106 attached to an upper , proximal end of the first face plate 102 . the semiannular arm 106 has a ramp extension 108 that extends distally from a lower portion 106 l of the semiannular arm below and adjacent to the lower edge of the chain guide bar 36 . the ramp extension 108 has an exterior surface s that extends proximally and exteriorly at an oblique angle with respect to the plane that contains the exterior surface 36 e of the chain guide bar 36 . most detachments of a cutting chain 30 from the chain guide bar 36 are minimal deviations , temporary , and self - correcting , and we do not want the device 100 to derail the cutting chain for such minimal deviations . accordingly , the entrance surface s is disposed at some minimal distance below the lower edge of the chain guide bar 36 . that minimal distance should be greater than the overall height of the cutting chain 36 in interior , elevational view ; that is , the minimal distance will ordinarily be in the range of 4 to 6 cm , more or less for a three - quarter pitch cutting chain . the optimal minimum distance will vary somewhat among chain saws and with the design and dimensions of their cutting chains . in any case , the optimal minimum distance must be experimentally determined for each chain saw to prevent unnecessary derailings of the cutting chain 30 . the semiannular arm 106 coaxially surrounds and engages the semiannular periphery of the proximal ring 38 p of the chain bar mount . in the event that the cutting chain 30 detaches from the groove g of the chain guide bar 36 during operation of the chain saw 10 , the cutting chain would slide exteriorly along the oblique surface s to the exit surface s ′ of the ramp extension 108 , which is preferably disposed well exteriorly from the drive sprocket 42 ; the inevitable result is that the cutting chain is thereby removed from the drive sprocket 42 , loses kinetic energy , and slows to a stop while still contained within the chain saw box 12 . in the first embodiment 100 , the chain catcher means 52 comprises a flange 110 at a proximal end portion 102 p of the first face plate 102 . the flange 110 extends from an upper edge to a lower edge of the first face plate 102 and protrudes exteriorly therefrom enough to be an effective barrier against a detached or broken chain flying distally past its location during operation of the chain saw 10 . in addition , an upper portion of the semiannular arm 106 also helps catch a detached or broken piece of cutting chain 30 . accordingly , if any portion of a detached 30 moves from the semiannular arm 106 in the distal direction past the drive sprocket 42 it will hit the flange 110 and be stopped . preferably , the face plate has a second flange 112 that is similar in shape and dimension to the flange 110 , but is disposed along an upper edge of the first face plate 102 p to further confine the movement of a detached chain or chain shot . a second embodiment of the device 200 is depicted in fig1 - 14 . in the device 200 , for ramp means 54 there is provided a horseshoe - shaped arm 204 that includes a bight portion 204 b . the bight portion 204 b is dimensioned for coaxial , coplanar , close - fitting , surrounding engagement of the proximal ring portion 38 p of the bar mount 38 . the ramp means 54 further includes a ramp 206 that extends proximally and exteriorly from ( or near ) the lower , distal end 204 l of the arm 204 . the ramp 206 is disposed below the chain guide bar 36 , and has an entrance surface slightly exterior to a plane that contains the interior surface of the chain guide bar ( e . g ., 1 cm to 3 cm ) and an exit surface that is exterior to the chain guide bar — that is , the ramp crosses over the chain guide bar 36 . with the ramp 206 so positioned , if , during operation of the chain saw 10 , the cutting chain 30 becomes detached from the groove g , the cutting chain swell into a more circular configuration and will be deflected off and exteriorly away from the drive sprocket 42 , depriving the cutting chain of additional kinetic energy . previous comments regarding the minimum and maximum distances between the exterior surface of the chain guide bar 36 and the ramp extension 108 of the first embodiment of the device 100 apply as well to the ramp 206 of the second embodiment 200 . preferably , the arm 204 is attached to a lower , ring portion of the bar mount by a weld or other suitable means . for chain catcher means 52 , the second embodiment of the device 200 provides a guard 208 that is semiannular in exterior elevational view and is exteriorly spaced apart from the drive sprocket 42 . the chain catcher means 52 of the second embodiment 200 further includes a chain catcher mounting plate 212 that is shaped and dimensioned for close - fitting attachment by fasteners to an exterior surface of the chain tensioner 46 . preferably , the guard 208 is coaxial with the drive sprocket 42 , is semitoroidal as depicted in fig1 - 14 , and has an outer radius greater that the outer radius of the drive sprocket , but less that the outer radius of the proximal ring 38 p of the bar mount 38 . as used herein , a first component of the device 100 , 200 is “ below ” a second component of said device if , and only if , having reference to fig5 a , the first component is disposed lower than the second component . all components of the device 100 , 200 preferably comprise steel , but may comprise any substances having sufficient strength , hardness , and durability to adequately perform the functions required of those components by the invention . although specific embodiments of the invention have been illustrated and described herein , it will be appreciated by those of ordinary skill in the art that modifications and changes in the devices 100 , 200 set forth above will be possible without departing from the spirit and scope of the invention . accordingly , it is intended that the following claims be interpreted to embrace all such modifications and changes , and equivalents thereof , as will be apparent to one having ordinary skill in this technology .
a device for deflecting a detached cutting chain off the drive sprocket of a chain saw in order to deenergize and arrest it . a ramp provides a surface disposed below the chain guide bar , which surface is oblique with respect to the chain guide bar , slightly below a lower edge of the chain guide bar and obliquely angled with respect to a plane that contains the exterior surface of the chain guide bar , and distal to the drive sprocket . sliding engagement of a detached cutting chain with the oblique surface moves the cutting chain exteriorly away from the chain guide bar and off the drive sprocket . a chain catcher is also provided to arrest the detached cutting chain and / or chain shot portions thereof .