fig1 - 3 show one embodiment of quick attach rotary mower blade system 100 for use with one more rotary mower blades under a mower deck . the quick attach rotary mower blade system may be used to manually remove and install mower blade 138 to mower spindle 104 without tools . all of the components of the quick attach rotary mower blade system , including blade holder 102 , coil spring 124 , plunger 126 , and shoulder bolt 132 , remain attached to the spindle when the mower blade is removed . in one embodiment , the quick attach mower blade system may include blade holder 102 which may be a one - piece steel or hard plastic molded structure that may be secured to spindle 104 . spindle 104 may be rotatably mounted to flange 106 which may be attached with threaded fasteners 108 to the underside of a mower deck . the blade holder may have outer frame 113 and a pair of l - shaped arms 118 that extend downwardly from opposing sides of the outer frame to hold a mower blade . each l - shaped arm may include a generally vertical part extending down from the frame , and a generally horizontal part that is under the mower blade when the mower blade is installed . the horizontal part may be spaced apart from the outer frame sufficiently so that mower blade 138 may fit between the horizontal part and the outer frame . the blade holder also may have a central opening 112 that is coaxial with the internally threaded central opening 110 of spindle 104 , and a rim 127 where washer 122 may be positioned . in one embodiment , the quick attach rotary mower blade system may include a spring loaded plunger 126 . coil spring 124 may provide a downward spring force axially against plunger 126 . as a result , the face 128 of the plunger may press down against mower blade 138 . the coil spring may be positioned between washer 122 and / or blade holder 102 , and plunger 126 . the coil spring may have a conical shape to minimize the spring &# 39 ; s thickness in its compressed state . plunger 126 may be a sheet metal component having a downward face 128 and a drum shape . the plunger also may have a plurality of retaining fingers 130 that extend upwardly from the plunger &# 39 ; s outer circumference . each retaining finger may extend through a notch 116 in blade holder 102 . each retaining finger may contact a stop 114 at the base of each notch to limit how far the plunger may extend from the blade holder , and retain the plunger to the blade holder . notches 116 , stops 114 , and rim 127 may be provided on shelf 121 between central opening 112 and outer frame 113 of the blade holder . in one embodiment , the quick attach mower blade system may include shoulder bolt 132 . the shoulder bolt may be threaded to the internally threaded opening 110 of spindle 104 , and remains secured to the spindle whenever the mower blade is removed . the shoulder bolt may be threaded to the spindle by turning the shoulder bolt &# 39 ; s head 136 . adjacent the head , the shoulder bolt may have an unthreaded shoulder 134 having a slightly larger diameter than head 136 , and an axial length of about ½ inch to about 1 inch . the unthreaded shoulder 134 also may have a larger diameter than opening 123 in washer 122 , so the shoulder bolt and washer may be used to secure the blade holder on the spindle . however , the unthreaded shoulder 134 may have a smaller diameter than central opening 129 in plunger 126 , so the plunger may slide up and down the shoulder bolt during installation of the mower blade . the unthreaded shoulder also may have a slightly smaller diameter than central opening 140 in the mower blade , so the mower blade may be installed or removed by sliding over the shoulder bolt , without removing the shoulder bolt . in one embodiment , the quick attach mower blade system may include a pair of upwardly facing protrusions 120 on the blade holder . the protrusions may engage a pair of holes 142 in the mower blade . adding holes to the mower blade requires a modification to conventional mower blades , but is relatively easy and inexpensive . one of the upwardly facing protrusions may be provided on the horizontal part of each l - shaped arm . the pair of protrusions 120 may be located asymmetrically on the l - shaped arms , or may have different shapes or sizes . similarly , the pair of holes 142 may be located asymmetrically on the mower blade , or may have different shapes or sizes . as a result , the mower blade may be installed in only one position and not upside down . in one embodiment , an operator may install mower blade 138 onto the quick attach mower blade system easily and without tools . first , as shown in fig3 , the operator may manually position the mower blade in the gap between the pair of l - shaped arms 118 . the operator then may push the mower blade up against plunger 126 to compress coil spring 124 . the operator may push the mower blade up high enough for the bottom of the blade to clear protrusions 120 , and then may pivot the mower blade on its central axis 140 over the protrusions onto the l - shaped arms . the operator may pivot the mower blade until the mower blade contacts the vertical part of each l - shaped arm . at this point , the pair of holes 142 in the mower blade should be positioned over the pair of upwardly extending protrusions 120 . when the operator stops pushing the mower blade up , the plunger may urge the mower blade down toward the horizontal part of the l - shaped arms , pushing the pair of holes 142 over the pair of protrusions 120 . after installation , as shown in fig2 , the coil spring may continue to apply spring force against the plunger , holding the mower blade in place and holding protrusions 120 inside holes 142 . in one embodiment , an operator also may remove mower blade 138 from the quick attach mower blade system easily and without tools . first , the operator may push the mower blade up against plunger 126 to compress coil spring 124 , until protrusions 120 are out of holes 142 . while continuing to push the mower blade up , the operator may pivot the mower blade over the protrusions and toward the gap between the pair of l - shaped arms 118 . the operator may stop pushing the mower blade up when the mower blade reaches the gap . having described the preferred embodiment , it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims .
a quick attach rotary mower blade system includes a blade holder secured to a mower spindle with a shoulder bolt , a pair of upwardly extending protrusions on the blade holder , and a spring biased plunger extending downwardly from the blade holder . a rotary mower blade has a center hole that slides over the shoulder bolt , compresses the spring biased plunger , and rotates over the protrusions to an engaged position .