fig1 - 6 depict one embodiment of a reel cutting unit according to this invention generally as 2 . cutting unit 2 is very similar to cutting unit 2 disclosed in u . s . pat . no . 5 , 628 , 169 , owned by the toro company , the assignee of this invention , and the &# 39 ; 169 patent is hereby incorporated by reference for teaching various details of cutting unit 2 and the gang mower ( not shown herein ) with which cutting unit 2 may be used . a plurality of cutting units 2 may be placed in a gang configuration on the gang mower disclosed in the &# 39 ; 169 patent or on other known reel gang mowers , including toro &# 39 ; s reelmaster 3100 - d . by way of overview , cutting unit 2 comprises a pair of laterally spaced apart side plates 4 that may be joined by various other members , such as a top wall 6 or a back wall ( not shown ). a rotatable reel 8 having a plurality of helical blades is rotatably journalled between side plates 4 of cutting unit 2 . a bedknife 10 is placed beneath a lower portion of the orbit of reel 8 such that the blades of reel 8 will sweep grass against a sharpened cutting edge of bedknife 10 for cutting the grass using a shearing action . front and rear ground engaging rollers 12 and 14 extend between side plates 4 for allowing cutting unit 2 to roll independently on the ground during forward motion of the gang mower ( not shown ) to which cutting unit 2 is attached . the structure of cutting unit 2 as described thus far is conventional and corresponds to that disclosed in the &# 39 ; 169 patent . a cutting unit carrier frame 16 overlies cutting unit 2 and for the purposes of longitudinal propulsion is , in effect , part of the frame of the gang mower . in other words , carrier frame 16 is moved forwardly or rearwardly as the frame of the gang mower moves forwardly or rearwardly . carrier frame 16 includes a hollow roll sleeve 18 for mounting on one of the lift arms of the gang mower to allow carrier frame 16 and cutting unit 2 to roll together about a longitudinal roll axis . however , for the purposes of this invention , this rolling action is not important and could be dispensed with if so desired , in which case roll sleeve 18 would be absent and carrier frame 16 could be coupled in a non - rolling fashion to the lift arm . again , this type of carrier frame 16 with a roll sleeve 18 is conventional and corresponds to that disclosed in the &# 39 ; 169 patent . a four - bar linkage 20 that includes front and rear pivot links 22 and 24 is used to couple each side plate 4 on cutting unit 2 to one side of carrier frame 16 . as shown in fig1 and 2 , pivot links 22 and 24 of each four - bar linkage 20 are pivotally coupled at their upper ends to carrier frame 16 and at their bottom ends to the adjacent side plate 4 of cutting unit 2 . pivot links 22 and 24 converge towards one another as they extend downwardly . once again , this type of four - bar linkage 20 including the converging front and rear pivot links 22 and 24 is conventional and corresponds to that disclosed in the &# 39 ; 169 patent . in cutting unit 2 of this invention , front pivot link 22 attaches to the side of carrier frame 16 at a single pivot location as show at 26 in fig1 - 6 . there are two holes 28 shown in the side of carrier frame 16 above and below the single pivot location 26 of front pivot link 22 implying that front pivot link 22 could be repositioned on carrier frame 16 , but this is not the case . the additional holes 28 that are shown are not the right size for receiving the pivot pin or bolt that secures the upper end of front pivot link 22 and are used for attaching a grass catcher ( not shown ) to cutting unit 2 . thus , the reader hereof should ignore the two holes 28 shown above and below the single pivot location 26 of front pivot link 22 as these holes 28 form no part of this invention . insofar as cutting unit 2 of this invention shows a single pivot location 26 for front pivot link 22 on carrier frame 16 , this is also conventional and corresponds to that disclosed in the &# 39 ; 169 patent . however , unlike the cutting unit disclosed in the &# 39 ; 169 patent , cutting unit 2 of this invention includes a plurality of holes 30 to which the upper end of rear pivot link 24 can be pivotally attached . all holes 30 are sized to receive the pivot pin or bolt on the upper end of rear pivot link 24 and rear pivot link 24 can be interchangeably and alternatively coupled to any one of the holes 30 . holes 30 are arranged on side plate 4 such that holes 30 are longitudinally spaced apart by approximately 1 inch from one another , the holes 30 being disposed in an arc that is at a constant distance or radius from the pivot axis of the lower end of rear pivot link 24 . thus , there is a front hole 30 f , a middle hole 30 m , and a rear hole 30 r with front hole 30 f being higher than middle hole 30 m and middle hole 30 m being higher than rear hole 30 r . referring now to fig3 , when the upper end of rear pivot link 24 is coupled to middle hole 30 m , pivot links 22 and 24 converge at a focal point that establishes a first virtual pull point 32 a for cutting unit 2 . the propulsive forces that are transmitted from carrier frame 16 to cutting unit 2 act on cutting unit 2 as if they were being directly applied to cutting unit 2 at pull point 32 a . as seen in fig3 , pull point 32 a is located slightly below and slightly rearwardly of the centerline of reel 8 . the location of pull point 32 a is substantially longitudinally aligned with the center of gravity ( c . g .) of cutting unit 2 . thus , there is no moment arm tending to cause cutting unit 2 to tip or pivot about the pull point ( or there is only a very small moment arm tending to tip or pivot cutting unit 2 slightly towards rear roller 24 ), such that pull point 32 a establishes a generally neutral or balanced fore - and - aft weight distribution on cutting unit 2 . there is approximately as much weight on front roller 22 as on rear roller 24 . pull point 32 a is the pull point which would probably be used most often on cutting unit 2 . however , with the addition of the front and rear holes 30 f and 30 r for rear pivot link 24 , the user has the option of connecting the upper end of rear pivot link 24 to one of these other holes . if the user selects rear hole 30 r as shown in fig4 , a second virtual pull point 32 b is established that is shifted upwardly and forwardly from pull point 32 a . since the location of the c . g . is still the same , the longer moment arm established by this shift in pull point 32 b creates a tail heavy fore - and - aft weight distribution that shifts more weight to rear roller 24 as compared to front roller 22 . with less weight now on front roller 22 , the aggressiveness of cutting unit 2 in cutting grass is lessened . in some grass conditions , as explained hereafter , this is desirable . similarly , by referring to fig5 , one can see that use of front hole 30 f establishes a third virtual pull point 32 c that is moved downwardly and rearwardly from pull point 32 a . in fact , pull point 32 c preferably moves in back of , at least slightly , the c . g . of cutting unit 2 . this creates a nose heavy fore - and - aft weight distribution in which more weight is placed on front roller 22 as compared to rear roller 24 . this increases the aggressiveness of cutting unit 2 in cutting grass , which can be desirable in other grass conditions . as a result , user can easily and quickly vary the aggressiveness of cut by moving the upper end of rear pivot link 24 from one hole 30 to another , a more aggressive cut being provided by front hole 30 f , a cut of normal aggressiveness being provided by middle hole 30 m , and a cut a lessened aggressiveness being provided by rear hole 30 r . one way a user can use this feature is to configure the front and rear cutting units 2 f and 2 r of a reel gang mower differently as shown in fig6 . in this depiction , rear pivot links 24 of front cutting units 2 f are coupled to middle hole 30 m to provide a cut of normal aggressiveness . however , if certain grass conditions are present , trailing cutting units 2 r will leave marks due to double cutting in those portions of the cut grass swath in which trailing cutting units 2 r overlap the sides of front cutting units 2 f . if this occurs , the applicants have found that configuring rear cutting units 2 r differently from front cutting units 2 f can effectively solve or mitigate this problem , namely by using rear holes 30 r to provide a less aggressive cut on rear cutting units 2 r . the less aggressive cut is visually suggested in fig6 by showing front roller 22 of rear cutting units 2 r up slightly off the ground . this is an exaggeration since front roller 22 would be in contact with the ground when cutting grass , but the exaggeration is simply meant to be a visual indicator that there is less weight on front rollers 22 of rear cutting units 2 r than there is on front rollers 22 of front cutting units due to the use of the rearward hole location 30 r on rear cutting units 2 r as opposed to the use of middle hole location 30 m on front cutting units 2 f . thus , this invention and the versatility in the aggressiveness of cut that is provided by multiple holes 30 for rear pivot link 24 can enhance the aftercut appearance of the cut grass swath , which is obviously desirable to some users of reel gang mowers . however , the example of how this might be done set forth in the preceding paragraph is not meant to be limiting . other combinations of different holes 30 might be used at the same time on the front and rear reel cutting units 2 f and 2 r in different grass conditions . it would also be the case that the same holes 30 might be used on all cutting units 2 of a given reel gang mower , i . e . both the front and rear reel cutting units 2 f and 2 r are using middle holes 30 m at one time in one set of grass conditions , or front holes 30 f at another time in a second set of grass conditions , or rear holes 30 r at a third time in a third set of grass conditions . in some cases , a rear roller brush attachment ( not shown ) is installed atop rear roller 24 of cutting unit 2 to help keep rear roller 24 free of grass clippings or other debris . this has some impact on the location of the c . g . and shifts the c . g . further rearwardly . thus , the supposedly neutral fore - and - aft weight distribution of cutting unit 2 using pull point 32 a is changed into a slightly more tail heavy weight distribution which , in some grass conditions , might not be desired . thus , with a rear roller brush attachment in place , shifting the upper end of rear pivot link 24 to front hole 30 f can help compensate for the added weight of rear roller 24 brush attachment and helps maintain a generally neutral fore - and - aft weight distribution . the various adjustments holes 30 that are used to adjust the pull point locations have been shown in connection with the upper end of rear pivot link 24 , but this need not necessarily be the case . the virtual pull point location could have been varied by placing the series of adjustment holes 30 on the side plate of reel cutting unit 2 rather than on carrier frame 16 , or adjustment holes 30 could have been used in connection with the upper or lower ends of front pivot link 22 . moreover , adjustment holes 30 could be used in different pivot linkages in which actual pull points , rather than virtual pull points , are used . for example , such a pivot linkage might include one where a single pivot link or arm transfers propulsive force from the gang mower frame to the reel cutting unit . such a single pivot link would be connected at one end by a pivot connection to the gang mower frame and at the other end by a pivot connection to the reel cutting unit . in this case , the pull point is located at the actual location at which the other end of the pivot link connects to the reel cutting unit . in this case , the reel cutting unit might have a plurality of adjustment holes thereon for receiving the other end of the pivot link for varying where the pivot link actually connects to the reel cutting unit . thus , this invention is applicable whether actual or virtual pull points are employed in transferring propulsive force from the gang mower frame to the reel cutting unit . various other modifications of this invention will be apparent to those skilled in the art . for example , and not by way of limitation , rather than use a set of discrete adjustment holes 30 on carrier frame 16 , the upper end of rear pivot link 24 could be shifted in an infinite manner if it were connected to carrier frame 16 by some type of threaded adjuster that could be rotated to move the upper end of rear pivot link 24 in a fore - and - aft direction . accordingly , the scope of this invention will be limited only by the appended claims .
a reel gang mower has a row of front reel cutting units and a row of rear reel cutting units that cut an unbroken swath of grass in each pass . each cutting unit is connected for propulsion to the mower frame by a four - bar linkage having front and rear pivot links that converge towards a focal point that establishes a virtual pull point through which propulsive force acts on the cutting unit . the rear pivot links can attach to the mower frame at a selected one of different attachment points to thereby longitudinally shift the pull point fore - and - aft relative to the center of gravity of the cutting unit , thus changing the fore - and - aft weight distribution . the rear cutting units in the gang can be configured to have a tail heavy weight distribution relative to the front cutting units to help eliminate marking in the overlap areas between the cutting units .