the illustrated embodiment is especially adapted for forming hay into compact blocks . it may be incorporated within a self - propelled vehicle and adapted to operate as the vehicle is moving ahead and picking up hay , or it may be fixed in position and supplied with hay by means of some sort of conveyor or feeding mechanism . a typical vehicular installation might comprise a pickup and feed mechanism which would be located forwardly of the block forming mechanism . it would function to pick up hay or the like and feed it into the block forming mechanism . the vehicular machine would also include some sort of mechanism for collecting the blocks as they leave the block forming mechanism . the present invention relates only to the block forming mechanism . hence , only an embodiment of the block forming mechanism is shown and described . referring to fig1 - 3 , the preferred embodiment is intended for use in a vehicular machine and is oriented to receive hay which is picked up by the machine and moved relatively rearwardly along a line coinciding with the path of travel of the machine . the basic components of the block forming mechanism are a pair of presser wheels 10 , 12 which are mounted for rotation about first and second axes , x , x &# 39 ;. the presser wheels 10 , 12 are obliquely related and define between them an acute angle which by way of example may be about 25 °- 35 °. also by way of example , each wheel 10 , 12 may measure about 25 - 30 inches in diameter . as shown by fig1 - 3 , the wheels 10 , 12 may be mounted onto a frame 14 comprising tubular upper and lower horizontal members 16 , 18 and tubular vertical side members 20 , 22 . each presser wheel 10 , 12 is mounted at the end of an elongated shaft which in turn is mounted for rotation by axially spaced apart bearings within bearing housings 24 , 26 . bracket means 28 interconnected between bearing housing 26 and frame 14 serves to mount presser wheel 12 for rotation in a fixed position . parallelogram linkage , comprising spaced apart pairs of arms 30 , 32 , form an adjustable mount for wheel 10 . an upper link 32 and a lower link 32 are each pivotally connected at one end to the frame member 16 , 18 and at the opposite end are pivotally connected to the bearing housing 24 . arms 30 are similarly pivotally connected to both the frame members 16 , 18 and the bearing housing 24 . the four pivotal axes are located to define a parallelogram , so that upon movement of the linkage , by application of a force to the forward ends of arms 30 , the bearing housing 24 , and hence the wheel 10 , will move laterally relative to the fixed wheel 12 , but without an appreciable change in the angle between the two wheels 10 , 12 . as will hereinafter be explained in greater detail , the movable mounting of wheel 10 provides a way of adjusting the lateral spacing of the two wheels 10 , 12 where they come generally together at the rear of the mechanism . wheel 12 may be positively driven by a motor 34 and wheel 12 may in turn drive wheel 10 . a pair of support arms may be bracketed onto the bearing housing 26 , to extend forwardly and support between them a linear hydraulic motor 38 . the cylinder or piston housing of motor 38 is connected to arms 36 for pivotal movement about a vertical axis . the free end of a piston rod 40 is connected to a vertical member 42 which is connected at its upper and lower ends to the forward ends of the arms 30 , for pivotal movement about a vertical axis . extension and retraction of the linear hydraulic motor 38 applies a force on the forward ends of arms 30 which makes the parallelogram mechanism 30 , 32 function to shift presser wheel 10 in position relative to presser wheel 12 . each wheel 10 , 12 may have a disc body 44 onto which are secured presser teeth 46 and annular wall forming rings 48 , 50 . the presser teeth 46 may be formed in segments which are secured to the disc bodies 44 , such as by means of countersunk bolts 52 , for example ( fig4 ). fig1 shows the segmented construction of the rows of teeth on wheels 10 , 12 . fig4 shows the cross - sectional configuration of the tooth segments . as also shown by fig4 an annular channel 54 may be formed in each disc body 44 to receive base portions of the tooth segments . as also shown by fig4 the two annular wall forming rings 48 , 50 may be bolted to the tooth segments , such as by use of countersunk bolts 56 which extend through openings formed in the rings 48 , 50 and thread into threaded openings formed in the tooth segments . as also best shown by fig4 the two rings of teeth 46 are identical and when they come together at the rear of the mechanism they substantially mesh similar to the way gear teeth mesh . ring 48 is located radially outwardly of the teeth 46 on disc 10 . also , whereas , the teeth 46 and the ring 48 both project generally axially from disc body 44 , the ring 48 projects axially a greater distance than the teeth 46 . similarly , teeth 46 and ring 50 on wheel 12 both project axially from the disc body 44 and ring 50 project axially a greater distance than the teeth 46 . as a result , when the teeth come together at the rear of the mechanism to define chambers or pockets between them , in the region of such chambers or pockets the outer ring 48 occupies a position radially outwardly of both sets of teeth 46 and the ring 50 occupies a position radially inwardly of both sets of teeth 46 . thus , the pockets are defined on their sides by the surfaces of the mating teeth 46 and are closed at their ends by the rings 48 , 50 . as shown by fig1 - 3 , a trough - like structure 58 , having opposed side walls 60 , 62 and a bottom 64 , leads generally tangentially into the lower portion of the space between the two rows of teeth 46 . preferably , the hay or other substance being treated is delivered into the mechanism at a rate of travel equal to or slightly greater than the speed of travel of the teeth 46 , to ensure a good flow of hay into and through the block forming region . referring now to fig5 incoming hay or the like is trapped axially between the two sets of teeth 46 . as the teeth come together they both compress and compact the hay and move it on through the mechanism . the trapped hay exerts a resistance force on both wheels 10 , 12 , so that the pressure of the hay will move the movable wheel 10 outwardly in opposition to the force applied by cylinder 38 until a predetermined size of the hay blocks is achieved . fig7 shows the results of a thicker block setting of cylinder 38 than fig5 . as the teeth 46 move apart downstream of the location of maximum compaction and minimum pocket size , the pockets open up and surface portions of the teeth 46 roll the blocks over and start them along a path of travel away from the block forming mechanism . as shown by fig1 the bottom wall 64 of the feed channel curves upwardly to help guide the hay or the like into the space axially between the two sets of teeth 46 . similarly , a curved shield 68 ( fig2 and 3 ) is located between the two wheels 10 , 12 , for directing the loose hay downwardly to the two rows of teeth 46 . the bottom 64 of channel 58 forms a boundary for the hay radially outwardly of the teeth 46 . the curved shield 68 forms a similar boundary radially inwardly of the teeth 46 . referring to the schematic diagram portion of fig2 linear motor 38 may be a double acting hydraulic motor provided with a conventional control valve 70 . drive motor 34 may be a hydraulic motor having a feed line 72 and a return line 74 . a variable displacement pump 74 may be provided for supplying hydraulic fluid , to pump 74 via a conduit 76 , into the motor feed line 72 . according to an aspect of the invention , a pneumatic sensor or the like is mounted to be actuated by movement of either rod 40 or arm 30 . the actuator may comprise an air cylinder 78 having an air chamber 80 on one side of its piston 82 and a spring 84 on the opposite side . air may be delivered into chamber 80 via a delivery line 86 which includes a modulating pressure type control valve 90 . a mechanical connection , such as a lever 92 may extend between the piston rod 94 and the displacement control portion of pump 74 . a similar lever 96 may be interconnected between rod 40 and valve 90 so that movement of rod 40 will result in movement of lever 96 and a change in position of valve 90 . valve 70 is operated to move cylinder 38 so that cylinder 38 will in turn move the movable presser wheel 10 in position relative to the fixed presser wheel 12 for the purpose of establishing a desired density of the blocks 66 . control valve 90 is operated to establish a desired displacement of pump 74 . then , during operation , if for some reason the flow rate of hay into the compacting pockets decreases slightly , resulting in some movement of movable presser wheel 10 and its mounting towards fixed presser wheel 12 and its mounting , such movement will be sensed by the modulating valve 90 . valve 90 will react to change pressure within chamber 80 , causing movement of lever 92 to decrease the displacement of pump 74 . flow of hydraulic fluid to motor 34 is reduced and in turn the rotation speed of the presser wheels 10 , 12 is reduced . this results in an increase of the cube thickness to bring it back up to the desired size . as will be evident , the control mechanism will also function to automatically increase the rotational speed of wheels 10 , 12 , to reduce cube thickness . the illustrated embodiment has been especially adapted for use to compact loose hay into feed blocks . however , it is to be understood that the mechanism might also be used for compacting other types of vegetation into feed blocks , or to compact various types of matter ( e . g . straw , grasses , etc .) into blocks for use as fuel , or any other purpose . accordingly , the expression &# 34 ; hay or the like &# 34 ; is used herein to mean any relatively loose form material that can be compacted together under pressure to form blocks .