referring now to the drawings and particularly to fig1 a modular disc cutterbar incorporating the principles of the parent application can best be seen in a configuration in which the disc cutterbar is conventionally utilized . for a more detailed description of a conventional modular disc cutterbar and various configurations thereof reference is made to u . s . pat . no . 5 , 996 , 323 . the disclosure in that patent is hereby incorporated herein in its entirety by reference . cutterbar 30 is mounted in a disc mower 10 having a support frame 11 connected to the three - point hitch mechanism 3 of a tractor t on which the mower 10 is carried in a conventional manner . the disc mower 10 receives operative power from the conventional tractor power take - off shaft 5 . the mower drive mechanism 15 receives the rotational power from shaft 5 and transfers the rotational power to a gearbox 17 , which in turn transfers the rotational power to the cutterbar drive mechanism . an alternative configuration for the disc cutterbar would be to incorporate the cutterbar in a disc mower - conditioner . this well - known configuration is shown in more detail in u . s . pat . no . 5 , 761 , 890 , which is hereby incorporated herein in its entirety by reference . one skilled in the art and knowledgeable about commercial applications of disc cutterbars will readily recognize that there are other specific configurations of cutterbars to which the invention to be disclosed herein will be applicable . such skilled individual will also readily recognize that the cutterbar need not necessarily be modular in construction . modular cutterbar 30 is formed from alternating cutterhead modules 40 and spacer modules 32 . each cutterhead module 40 , as best seen in fig1 - 3 , includes a hollow cast housing 41 ( fig3 ) having a shape to retain a low profile and to establish an oil reservoir 84 therewithin . as will be discussed in more detail below , the cutterheads 40 are gear driven and assembled in such a manner as to establish a specific timing relationship between adjacent units . more particularly , the cutterheads are arranged such that the knives 82 on adjacent units have overlapping cutting paths , but do not come into contact with each other . failure to maintain this timed relationship during operation will result in one unit hitting the adjacent unit ( s ), damaging the cutterheads ( and possibly initiating a chain reaction that damages all cutterheads ), the drive train of the cutterbar and / or tractor t . in such case , the damage is usually significant . referring now to fig2 , it can be seen that each cutterhead module 40 is provided with a forwardly positioned rock guard 65 and a skid shoe 70 that passes beneath cutterhead module 40 for engagement with the surface of the ground . the rock guard 65 has a conventional semi - circular configuration and is mounted to opposing forward mounting arms 35 of spacer module 32 adjacent to the corresponding cutterhead module 40 . one skid shoe 70 is mounted beneath each cutterhead module 40 to protect the cutterhead module from wear due to engagement with the surface of the ground . each skid shoe is formed as a generally planar body portion 71 with a mounting tab 73 affixed thereto and projecting upwardly . the body portion 71 is also formed with a forward end 72 that is bent upwardly to engage the corresponding rock guard 65 . modular drive mechanism 75 , seen in fig2 and 3 , is fully disclosed in the &# 39 ; 323 patent and reference is made thereto for a more complete description . broadly , within each cutterhead unit there is a two - piece hub , one inner hub and one outer hub , normally held together by a shear mechanism . the inner hub is connected to a drive shaft , and the outer hub , including an integral upper locking block , is connected to a rotatable knife support member . spaced below the outer hub is a fixed lower locking block . these components are arranged such that when a knife engages a solid or fixed object and a shear force generated adequate to cause the shear mechanism to fail , the outer hub rotates freely and drops ( preferably under the influence of a downward biased spring ) causing the upper and lower locking blocks to engage and the knife support member to cease rotation . by thus preventing the knives from rotating further , damage is prevented to the drive train of the cutterbar and between adjacent cutterhead units . ideally , the brake will stop rotation in one revolution or less . now , and more specifically , attention is directed to fig9 which shows an exploded perspective view of the inner hub 42 , the outer hub 43 and the lower locking block 44 . in the preferred embodiment , inner hub 42 is affixed to outer hub 43 by means of a layer of epoxy bonding surfaces 45 and 46 of the two hubs , respectively . by controlling the size of the bonded surface area of the two hubs , and knowing the shear strength of the epoxy , a specific shear point or force can be calculated so that failure will occur at the desired point and upon a specific impact . outer hub 43 includes an upper locking block made up of spaced - apart teeth 47 and 48 set within a circular recess 49 . lower locking block 44 comprises protruding cylindrical member 50 with spaced - apart teeth 51 and 52 . when assembled , as best seen in fig4 protruding cylindrical member 50 fits rotatably part way into cylindrical recess 49 . also as best seen in fig4 before failure of the layer 53 , cap 56 , inner hub 42 and outer hub 43 are fixed to and rotate with drive shaft 86 . after failure of layer 53 , outer hub 43 is free to rotate about drive shaft 86 , at least until the locking blocks engage . when engaged as discussed further below , the teeth on the respective locking blocks loosely fit together to prevent relative rotational movement between the two locking blocks . surfaces 45 and 46 may have generally any configuration or slope , so long as the outer hub can move into the locking position upon failure of layer 53 . the configuration shown has proven to be quite successful and functional . one of skill in the art will recognize that there are many types of epoxy available that will work in this environment . by way of example , successful operation has been experienced with an epoxy known as “ hp - 120 ” by loctite ®. a useful characteristic of epoxy is that only a very thin layer is required to hold the hubs together , and when it fails , the material all but disappears . this feature is quite valuable and important from a practical point of view in that the cleanliness of shear failure promotes quick operation of the brake . devices such as that shown in the &# 39 ; 662 patent listed above would , upon failure of the shear device , present metallic debris that would likely interfere with , and “ jam ” up the brake disclosed herein . while epoxy is disclosed as the preferred bonding or shear medium , there are other alternatives . for example , rubber , plastic , solder , brazing and the like could all be used . it is worthwhile to note that in the environment of a cutterhead , mechanical shear pins or similar fitted shear mechanisms tend to fail prematurely due to the fatigue experienced from the vibration and alternating stress inherent in the application . [ 0044 ] fig6 is an exploded cross - sectional view of the primary elements making up the preferred embodiment of the invention and is included herein for further clarity . the belleville washers ( springs ) 54 and 55 are mounted in an opposing manner and shown here in their compressed state , but it can be clearly seen that when assembled the washers will exert a downward bias on outer hub 43 . thus , if the epoxy bond 53 between the inner and outer hubs 42 , 43 is broken , outer hub 43 will be biased to move downwardly . [ 0045 ] fig7 and 8 are also presented for additional clarity . fig7 is a top plan view of lower locking block 44 taken along line 7 - 7 of fig6 . looking at this view and fig9 it can be seen that there are raised areas , or teeth , 51 and 52 extending partially around the circumference of the protruding cylindrically shaped portion 50 , forming lower interstitial areas 57 . fig8 shows that outer hub 43 includes a portion 59 which is referred to as the upper locking block . upper locking block 59 can be either integral with outer hub 43 , as shown here , or formed as a separate piece and affixed to outer hub 43 . teeth 47 and 48 are spaced apart , forming lower interstitial areas 58 . interstitial areas 57 and 58 are larger circumferentially than the respective teeth that are to be engaged therein . this difference in size is to allow time and space for the full engagement of the locking blocks upon failure of the shear layer . when assembled , the teeth of the two locking blocks are separated ; however , if the shear mechanism fractures , i . e ., the epoxy bond fails , outer hub 43 ( and because they are integral , upper locking hub 59 ) drops into lower locking block 44 - teeth 51 and 52 drop into spaces 58 , and teeth 47 and 48 go into spaces 57 . the two locking blocks are thus “ locked ” together , stopping the rotation of outer hub 43 ( and thus disc member 80 and knives 82 ). lower locking block 44 is fixed in place , i . e ., does not rotate and thus provides solid support for the locking function . the number and configuration of teeth on the locking blocks can , of course , vary depending upon several factors such as the hardness of the base materials , the speed of rotation , the mass of the cutterhead , and the timing required to stop the relative movement of the components . in addition , for similar reasons , it may be appropriate or beneficial to harden the teeth , add cushioning material to the interfering faces and / or add friction - reducing materials to the contacting surfaces . referring now to fig3 - 5 , inner hub 42 is detachably splined onto a drive shaft 86 having an integral driven gear 77 positioned within the oil reservoir 84 . inner hub 42 is affixed to outer hub 43 by a layer of epoxy 53 which , as described above , serves as a shearing device . a disc member 80 is detachably connected to outer hub 43 by bolts 81 so as to be rotatable therewith ( and thus knives 82 ). the drive shaft 86 is rotatably supported by a bearing block 78 detachably mounted to the cutterhead module housing 41 by bolts 79 . the bearing block 78 seals an opening in the top of the housing 41 through which the driven gear can be extracted from the oil reservoir 84 . when the cutterhead engages a fixed object of sufficient mass or rigidity to generate a shearing force on layer 53 , adequate to cause failure thereof , the inner and outer hubs 42 , 43 will separate and outer hub 43 will drop . in the preferred embodiment , outer hub 43 is biased downwardly by means such as belleville washers 54 and 55 working between cap 56 and outer hub 43 . fig5 shows this change in position of outer hub 43 ( has moved downwardly on shaft 86 ) in exaggerated form for illustrative purposes . the drive mechanism 75 in each cutterhead module 40 is coupled to the other cutterhead module drive assemblies 85 by a transfer shaft 94 that passes through the spacer module 32 , as best depicted in fig2 . the transfer shaft 94 is splined at each opposing end thereof to be finally received within either of the adjacent hubs to transfer rotational power thereto . referring now to the configurations of utilization of the cutterbar 30 as depicted in fig1 it can be seen that the drive mechanism 75 in a disc mower 10 receives rotational power from a gearbox 17 that is supported adjacent the inboardmost cutterhead module 40 . accordingly , the drive assembly 85 is connected directly to the output shaft ( not shown ) of the gearbox 17 . the transfer of rotational power to the remaining cutterhead modules 40 proceeds as described above . [ 0051 ] fig1 and 11 show an important alternative structure to the brake . in the brake described above , the outer hub drops down to allow the locking blocks to engage . a potential problem with this arrangement is that crop materials and debris can build up on the lower part of the structure and potentially hinder or interfere with the quick engagement of the brake . while one could take steps and develop structure to reduce or prevent the build up of materials , the structure shown in fig1 and 11 eliminates the potential problem by causing the outer hub to move upward on the drive shaft 86 to engage the brake . inner hub 110 is connected to outer hub 112 by shear bolt 114 . of course , instead of a shear bolt ( s ) a frangible layer as taught above could also be used as the shear device . between the inner hub 110 and outer hub 112 is a spring 116 , in this embodiment a known wave spring , biasing the outer hub 112 upwardly relative to inner hub 110 that is fixed to shaft 86 by , for example , splines . annular lip 118 on cap 117 forms a stop against further upward movement of inner hub 110 . thus , upon failure of the shear device , outer hub 112 moves upwardly away from inner hub 110 under the bias of spring 116 until it engages lip 118 of cap 117 . though the interlocking configuration of the locking blocks could be essentially the same as that described and shown in earlier figures , this embodiment shows a slight modification . lower locking block 120 has an annular recess 122 into which flange 124 of outer hub 112 fits . as best seen in fig1 , lower locking block 120 has spaced - apart annular lips 126 forming annular openings 128 which matingly match teeth ( not shown ) on flange 124 such that the teeth mate with openings 128 to lock outer hub 112 , when the shear device fails , in the manner described above . the dimensional relationship among the component parts is such that lip 118 stops upward movement of outer hub 112 at the same time the teeth on flange 124 move into openings 128 and engage the edges 130 of openings 128 . the instant invention is , as stated above , an improvement in the design of the braking device , i . e ., the outer hub 143 and the lower locking block 144 . the objective here is to prevent permanent damage to the locking mechanism due to excessive shear force , and to prevent damage to the cutterbar . attention is directed to the improvements of the instant invention as shown in fig1 , an exploded perspective view of the inner hub 42 , the outer hub 143 and the lower locking block 144 . in the preferred embodiment of the instant invention , inner hub 42 is affixed to outer hub 143 by means of a layer of epoxy bonding surfaces 45 and 46 of the two hubs , respectively . by controlling the size of the bonded surface area of the two hubs , and knowing the shear strength of the epoxy , a specific shear point or force can be calculated so that failure will occur at the desired point and upon a specific impact . outer hub 143 includes an upper locking block made up of spaced - apart teeth 147 and 148 set within a circular recess 149 . each of the teeth 147 and 148 has an energy absorbing end portion , 147 a and 148 a , respectively , affixed thereto . the material of which the energy absorbing portion is made may be any suitable material , such as , for example , a 50 % lead and 50 % tin , and may be in any suitable mixture , such as solder . the important selection criteria for the energy absorbing material is that it is softer than the parent material of the disc and locking blocks . lower locking block 144 comprises protruding cylindrical member 150 with spaced - apart teeth 151 and 152 . when assembled , as best understood by viewing fig4 ( and substituting the modifications of the instant invention ), protruding cylindrical member 150 fits rotatably part way into cylindrical recess 149 . also as best seen in fig4 before failure of the layer 53 , cap 56 , inner hub 42 and outer hub 143 are fixed to and rotate with drive shaft 86 . the interstitial spaces 157 between teeth 151 and 152 in lower locking block 144 include , adjacent the interface between the respective teeth and interstitial spaces , a 450 angle 157 a and a cavity 157 b . after failure of layer 53 , outer hub 143 is free to rotate about drive shaft 86 , at least until the locking blocks engage . when engaged , the teeth on the respective locking blocks drop into engagement to prevent relative rotational movement between the two locking blocks . as the respective teeth on the two locking blocks engage , the rotational force causes the energy absorbing material to deform . the energy absorbing material absorbs the kinetic energy of the rotating disc cutterhead . this decelerates the rotating disc to a slower rate , reducing the peak shear force applied to the locking blocks and eliminating damage to the structure . the angled surface 157 a forces the outer hub downward as the energy absorbing material is forced into the cavity 157 b , resulting in a more positive engagement of the locking blocks . since the energy absorbing material is forced into the cavity it prevents the outer hub ( and , thus , the disc cutterhead ) from rotating backwards . this keeps the disc cutterhead locked into a safe position and prevents it from being struck by the adjacent disc cutterheads . the number and configuration of teeth on the locking blocks can , of course , vary depending upon several factors such as the hardness of the base materials , the speed of rotation , the mass of the cutterhead , and the timing required to stop the relative movement of the components . in addition , for similar reasons , it may be appropriate or beneficial to harden the teeth , add cushioning material to the interfering faces and / or add friction - reducing materials to the contacting surfaces . it will be understood that changes in the details , materials , steps and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention . the foregoing description illustrates the preferred embodiment of the invention ; however , concepts , as based upon the description , may be employed in other embodiments without departing from the scope of the invention . accordingly , the following claims are intended to protect the invention broadly as well as in the specific form shown .
a disc cutterbar with at least one cutterhead having a two - piece mounting hub , one piece rotatably driven and the other supporting a knife for severing standing crop material , with an epoxy layer bonding the two pieces together and forming a shear device therebetween . a brake is associated with the knife - supporting piece whereby upon failure of said shear device , the knife - supporting piece is stopped from rotating within one revolution .