Tool drive assembly and related tool drive linkage, tool work implement assembly and tool

A landscape care tool can take the form of a vegetation-cutting tool incorporating circular-shaped blades having teeth or an earth-working tool incorporating hoeing tines. Drive linkage for such tool forms, as well as other tool forms, imparts linear movement in response to rotation of a shaft. The drive linkage includes a worm element which rotates with the shaft and a tooth carrier which moves linearly in response to rotation of the worm element. The worm element has one set of threads angled in one direction and a second set of threads angled in the opposite direction. The tooth carrier carries one tooth which engages threads of the first set of threads in order to move the carrier in one linear direction and a second tooth which engages threads of the second set of threads to move the carrier in the opposite linear direction. Variations in such characteristics as thread pitch spacing and pitch angle can be readily employed to substantially vary the characteristics of a drive assembly incorporating the linkage.

FIELD OF THE INVENTION 
The invention pertains to the field of landscape care apparatus, such as 
garden care tools, and to tool drive assemblies and drive linkage for such 
tools and for other forms of tools. 
BACKGROUND OF THE INVENTION 
Landscape care tools, such as garden care tools, most traditionally have 
drive trains based upon rotation of a shaft, most typically a shaft from a 
motor and, in many cases, an additional tool shaft coupled to the motor 
shaft. And a variety of such tools incorporate straight-forward rotational 
movement at the output part of the tool which performs the output 
operations. For example, line trimmers for cutting vegetation typically 
have rotating heads carrying extended lengths of line to perform the 
cutting. And snow throwers, which pick up and throw aside snow, and air 
blowers, which blow aside leaves and other cut or fallen vegetation, 
typically incorporate an impeller which rotates in straight-forward 
fashion. 
On the other hand, power hoes (or cultivators) based on the 
"back-and-forth" motion of hoeing tines, do not apply straight-forward 
rotation at their outputs. As indicated, they adopt a form of cyclical, 
reversing movement. Moulton, U.S. Pat. No. 4,351,396, issued Apr. 3, 1987, 
and to be reissued as Moulton et al., U.S. Reissue Pat. No. 33,238, on 
Jun. 26, 1990, and Motruk, U.S. Pat. No. 4,541,492, issued Sept. 17, 1985, 
are illustrative of such power hoes. The former emphasizes such apparatus 
incorporating a motor at the operating end of the tool and the latter 
emphasizes apparatus incorporating a motor at the other, user end of the 
tool. In both cases, the drive train incorporates a gear, an axle, and a 
crank-type arrangement with off-center throws, between the axle and the 
tines, to change straight rotational movement of a shaft to the 
back-and-forth movement of the tines. The assembly and operating 
instructions of HMC (Hawaiian Motor Co.), the assignee of the 
aforementioned patents, for apparatus including its Model 2370 cultivator 
and its Model 2371 and 3371 cultivator attachments are representative of 
up-to-date versions of the apparatus disclosed in such patents. 
Another form of landscape care tool, more specifically, a form of 
vegetation-cutting apparatus, which does not embody straight-forward 
rotation at its operating output, is a tool known as a reciprocator, which 
incorporates a pair of generally round blades having teeth, which each 
turn in one direction and then in the opposite direction through an angle, 
directly out-of-phase with one another, so that the teeth on one blade and 
the teeth on the other blade cut vegetation between one another. The 
magazine Power Equipment Trade, January 1989, at pages 28-31, directed to 
the RedMax Reciprocator (Model SGC22DL), is illustrative. Specifically, in 
that apparatus, there is a pinion gear-ring gear arrangement, between the 
rotating tool shaft and a crank shaft, such crank shaft having a pair of 
off-center throws. Each throw then drives a link which turns a short shaft 
for one of the pair of blades. Because of the geometry, the short shaft 
for one of the blades is inside the short shaft for the other. 
The present invention incorporates drive linkage which provides linear 
motion which is particularly beneficial in drive trains for cultivators 
and reciprocators which do not adopt straight-forward rotational movement 
at their operational outputs. The implementation is accomplished in a way 
which is an unusual blend of sophistication and simplicity. The invention 
is directed to a drive assembly incorporating such linkage, and to a tool 
incorporating such linkage, such as a tool for cutting vegetation through 
the rotational oscillation of circular-shaped cutting blades, or a tool 
for earth-working through the pendulum-like oscillation of hoeing tines. 
Specific linkage which converts rotational motion to the linear motion, 
and other specific linkage which provides a clutching function with 
damping with respect to linear motion, are also the subjects of the 
invention. Additionally, a form of blade assembly incorporating a pair of 
generally circular-shaped blades to cut vegetation through rotational 
oscillation, is provided. 
SUMMARY OF THE INVENTION 
In accordance with rotational-to-linear motion conversion aspects of the 
invention, there is provided a tool drive assembly for driving a tool work 
implement which is to perform operations on matter external to the tool 
through movement by the implement. The assembly includes: a prime mover; a 
driver shaft; first linkage to couple the driver shaft to the prime mover 
and rotate the driver shaft; an implement drive member to incorporate 
linear movement in response to the rotation of the driver shaft and to 
impart movement to the work implement through such linear movement: second 
linkage to couple the drive member to the work implement; and third 
linkage to impart such linear movement to the drive member in response to 
the rotation of the driver shaft. This third linkage, then, includes: a 
worm element to rotate with the driver shaft including a first set of 
threads angled in a first direction and a second set of threads angled in 
a second direction; and a tooth carrier carrying a first tooth to engage 
threads of the first set of threads in order to move the carrier in a 
first linear direction in response to the rotation of the worm element, 
and a second tooth to engage threads of the second set of threads in order 
to move the carrier in a second linear direction in response to the 
rotation of the worm element; wherein the tooth carrier is operatively 
connected to the implement drive member. 
In accordance with more detailed features of these aspects of the 
invention, the worm element, as initially described, further includes a 
first ramp sector and a second ramp sector; and the tooth carrier, as 
initially described, further carries a first ramp rider projection to ride 
the first ramp sector and move the second tooth towards engagement with 
the second set of threads, and a second ramp rider projection to ride the 
second ramp sector and move the first tooth toward engagement with the 
first set of threads. 
In accordance with other, more detailed features of the invention, the 
tooth carrier, as initially described, further carries a first catcher 
projection and a second catcher projection; and the third linkage, as 
initially described, further includes first and second catchers attached 
to the worm element, such first catcher to provide a barrier for the first 
catcher projection toward the extreme of the tooth carrier movement in the 
second linear direction, and the second catcher to provide a barrier for 
the second catcher projection toward the extreme of the tooth carrier 
movement in the first linear direction. 
In accordance with clutching aspects of the invention, a tool drive 
assembly for driving a tool work implement which is to perform operations 
on matter external to the tool through movement by the implement, 
includes: a prime mover, a driver shaft, first linkage, an implement drive 
member and second linkage, as initially described above; and third linkage 
to impart the referenced linear movement to the drive member in response 
to the referenced rotation of the driver shaft. Here, however, such third 
linkage includes: converter linkage including an input connector to rotate 
with the driver shaft, and an output connector to incorporate linear 
movement in response to the rotation of the input connector; and clutching 
linkage to differentiate such linear movement of the output connector and 
linear movement of the drive member including a shock-absorbing mechanism 
to compress and expand with such differentiated movement. 
In accordance with more detailed features of these clutching aspects of the 
invention, the shock-absorbing mechanism, as described, includes: a first 
shock-absorbing member, such as a spring, to compress with the referenced 
differentiated movement in a first linear direction and to expand with 
such differentiated movement in a second linear direction; and a second 
shock-absorbing member, such as a spring, to compress with such 
differentiated movement in the second linear direction and to expand with 
such differentiated movement in the first linear direction. 
In accordance with more comprehensive aspects of the invention, either the 
rotational-to-linear motion conversion aspects, or the clutching aspects, 
may be incorporated into a tool having a work implement to perform 
operations on matter external to the tool through movement by such 
implement, such as a circular-shaped cutting blade to perform operations 
through rotational oscillation or a hoeing tine to perform operations 
through a pendulum-like oscillation. 
Yet other, more focused aspects of the invention, focus on drive linkage to 
impart linear movement to a drive member in response to rotation of a 
shaft, in accordance with the third linkage of the rotational-to-linear 
motion conversion aspects of the invention as initially described. And in 
accordance with more detailed features, the pitch spacing or the size of 
the pitch angle, for the first set of worm element threads, as described, 
may be different than the pitch spacing or the size of the pitch angle, 
respectively, of the second set of worm element threads, as described. 
Also, such first set of threads may itself have a plurality of pitch 
spacings or a plurality of pitch angles or a cyclical series of pitch 
angle changes having a cycle of 360 degrees of rotation. 
In accordance with still other, more focused aspects of the clutching 
aspects of the invention, drive linkage to differentiate linear movement 
of an input connector and linear movement of an output connector includes 
a first shock-absorbing member and a second shock-absorbing member in 
accordance with the third linkage of the clutching aspects of the 
invention as initially described. 
And, finally, in accordance with work implement aspects of the invention, a 
work implement assembly for a tool for cutting, includes: a first 
generally circular-shaped blade to rotationally oscillate and cut, 
including a first set of teeth having a first tooth form along a first 
portion of the blade, and a second set of teeth having a second tooth form 
along a second portion of the blade; and a second generally 
circular-shaped blade to rotationally oscillate and cut in cooperation 
with the first blade, including a first set of teeth having the first 
tooth form along a first portion of the blade, and a second set of teeth 
having the second tooth form along a second portion of the blade. The 
blades are formed to face each other during their rotational oscillation. 
They each also include a third set of teeth having a third tooth form 
along a third portion of the blade.

DETAILED DESCRIPTION 
Referring to FIGS. 1-16, and by way of introduction, there is shown 
vegetation-cutting tool apparatus and earth-working tool apparatus, along 
with various assemblies and components thereof, as well as certain 
illustrative modifications, in accordance with the various aspects of the 
invention. 
In FIG. 1, a vegetation-cutting tool, of the type generally known as a 
reciprocator, incorporates an operating head having upper 24 and lower 26, 
generally circular-shaped blades. These blades cut by rotationally 
oscillating back and forth through an angle, directly out-of-phase, i.e. 
180 degrees out-of-phase, with one another, so that the vegetation is cut 
between the teeth of the two blades as they rotate past one another. The 
upper blade 24, shown disassembled from the top in FIG. 13A, has a low 
difficulty set of teeth 30 along a low difficulty portion of the blade 32, 
an intermediate difficulty set of teeth 34 along an intermediate 
difficulty portion of the blade 36, and a high difficulty set of teeth 38 
along a high difficulty portion of the blade 40. Similarly, the lower 
blade 26, shown dissembled and from below with reference to the view of 
FIG. 1, has a corresponding low difficulty set of teeth 42 along a low 
difficulty portion of the blade 44, an intermediate difficulty set of 
teeth 46 along an intermediate difficulty portion of the blade 50 and a 
high difficulty set of teeth 52 along a high difficulty portion of the 
blade 54. The low difficulty sets of teeth have a form adapted to cut 
relatively soft vegetation, such as grass or weeds, the intermediate 
difficulty sets have a form adapted to cut vegetation of intermediate 
difficulty such as twigs and other similar vegetation, and the high 
difficulty sets of teeth have a form adapted to cut high difficulty 
vegetation such as relatively hard wood. Of course, the form of teeth 
which the operator desires to employ at any given time can be applied to 
the vegetation to be cut by orienting the tool 20 such that the desired 
form of teeth move through the vegetation. 
In FIG. 4, a converter mechanism assembly 56, in the vegetation-cutting 
tool of FIG. 1, is shown. It converts rotational movement received from 
the elongated tool shaft 58 at the converter mechanism's input connector, 
socket member 60, to linear, back-and-forth movement at the mechanism's 
output connector, tooth carrier 62. The two halves of the housing 64 for 
the converter mechanism assembly are shown in FIGS. 7 and 8. With 
reference to the view of FIG. 4, the inside of the front half 66 of the 
housing, looking out from the paper toward such inside, is shown in FIG. 
7A, and an end view of such front half is shown in FIG. 7B. Similarly, 
again with reference to the view of FIG. 4, the inside of the back half 
70, of the housing, looking in the direction into the paper, is shown in 
FIG. 8A. And an end view of the back half 70, along with a cross-section 
showing a track sector 72 of the back half, are shown in FIGS. 8B and 8C, 
respectively. The components within the housing and components which 
immediately follow them in the drive train are shown in FIG. 5. 
Referring to FIG. 5, still with reference to the converter mechanism 
assembly 56 (FIG. 4), a worm element 74 and a tooth carrier 76 are shown. 
The worm element has an extender set of threads 78 and a retractor set of 
threads 80. As is apparent from the drawing, the extender set of threads 
are along the half of the worm element carrying the socket member 60 which 
directly connects to the tool shaft 58 (FIG. 4). And the retractor set of 
threads are along the other half of the worm element. As is also apparent 
from the drawing, the extender half are angled in one direction, with 
respect to the axis of rotation 82 of the worm element and the retractor 
threads are angled in the opposite direction. In the worm element 
embodiment of FIG. 5, such angles, also, are equal as well as opposite for 
the two sets. 
The tooth carrier 76 carries an extender tooth 84 and a retractor tooth 86. 
As the tool shaft 58 (FIG. 4) rotates, clockwise looking toward the worm 
element in the embodiment shown, the extender tooth 84 engages the 
extender threads 78 which push the extender tooth 84, and thus the tooth 
carrier 76, in the linear direction, down the drive train, along the tooth 
carrier axis 94, parallel to the axis of rotation 82 of the worm element 
78. However, the extender tooth 84 becomes disengaged from the extender 
threads while the retractor tooth 86 is becoming engaged with the 
retractor threads 80. As a result of this engagement on the retractor 
side, as the tool shaft continues to rotate, the retractor threads push 
the retractor tooth 86 back up the drive train, and thus the tooth carrier 
76 linearly, along the tooth carrier axis and parallel to the axis of 
rotation of the worm element, in the direction back up the drive train. 
The cyclical, linear back-and-forth movement of the tooth carrier 76, 
thus, continues repeatedly with the rotation of the drive shaft. 
An extender ramp sector 90 of the worm element 74 and an extender ramp 
rider 92 on the extender tooth 84 cooperate in rotating the tooth carrier 
76 through an angle about the tooth carrier axis 94 to accomplish the 
transition from the extender operation to the retractor operation. 
Similarly, a retractor ramp sector 96 of the worm element and a retractor 
ramp rider 98, on the retractor tooth 86, cooperate in rotating the tooth 
carrier back through the opposite angle to accomplish the transition from 
the retractor operation back to the extender operation. A retractor 
catcher 100, on the retractor end of the worm element 74, provides a 
safety barrier for a retractor catcher projection 102, on the retractor 
tooth 98, in the transition from the extender part of the cycle to the 
retractor part of the cycle. Similarly, an extender catcher 104, on the 
extender end of the worm element, provides a safety barrier for an 
extender catcher projection 106, on the extender tooth 84, in the 
transition from the retractor part of the cycle back to the extender part 
of the cycle. 
The extender part of the cycle, of course, refers to the movement of the 
tooth carrier linearly down the drive train and the retractor part of the 
cycle refers to the return of the tooth carrier in the opposite linear 
direction back up the drive train. 
Still referring to FIG. 5, and still generally by way of introduction, the 
tooth carrier 76, down the drive train, beyond the retractor tooth 86, has 
a spring 110 thereabout which may be descriptively termed the 
carrier-minus-case spring. The carrier 76 extends into a spring case 112 
through an opening (not shown) at the back of the case, and the spring is 
housed in the case against a spring stop 114 at the front end of the 
spring, which is attached on the front end of the tooth carrier 76, and 
against the back of the case which is behind the spring. There, then, is a 
corresponding case-minus-carrier spring 116 which is disposed between the 
spring stop 114 and the front of the spring case 116. This arrangement, 
relating to the springs and spring case, provides a damping, 
shock-absorbing mechanism between the back-and-forth linear movement of 
the tooth carrier 76 and the resulting movement of the spring case. This 
damping, shock-absorbing mechanism, then, is a clutching mechanism. 
In relatively normal or typical operations, the springs 110 and 116 will 
transfer the power from the tooth carrier 76 to the spring case 112 
essentially without compression or expansion. However, compression and 
expansion, with the damping, shock-absorbing, clutching effects, come into 
play where the typical, desired operation does not obtain. This may 
involve, for example, the engine operating at a faster speed (greater 
number of rotations per minute) than desired for the normal operation of 
the tool, or the work implements at the operating end of the tool 
encountering matter more difficult than that which is ordinarily expected, 
or of extreme difficulty which might otherwise break the apparatus, such 
as a relatively large rock or a wall. 
In FIG. 10, the components of the drive train for the vegetation-cutting 
tool operating end 22, following those in FIG. 5 are shown. And in FIG. 
11, some of the components, along the next section of the drive train, 
similarly are shown. Referring to FIG. 10, a reciprocator arm 118, a 
rocker 120 for the arm, a reciprocator yoke 122 and a reciprocator 
mounting piece 124 are designed to continue the back-and-forth linear 
movement along the drive train, while angling such linear movement away 
from along a parallel to the tool shaft 58 (FIG. 4) By varying the 
connection of the arm 18 to the rocker 120, the amount of yoke movement 
caused by a given amount of spring case 112 (FIG. 5) movement can be 
varied and, as a result, the angle of rotation through which the generally 
circular-shaped blades 24 and 26 (FIG. 1) rotate due to the movement of 
the spring case can be varied. The linear, back-and-forth movement of the 
yoke 122 acts on an upper blade pin 126 to oscillate the upper blade. The 
yoke also acts on a link pin 130 projecting from a link 132. That link 
then rotates a lower blade shaft 134 to which the lower blade is 
rotationally coupled, thus accomplishing the rotational oscillation of the 
lower blade directly out-of-phase, i.e., 180 degrees out-of-phase, with 
the upper blade. FIG. 12 shows the referenced structure from a 
cross-sectional perspective which includes the components of FIG. 11 as 
well as other related components. 
The same tool as shown in FIG. 1, alternatively, could be configured with 
the earth-working operating end of FIG. 2 in place of the 
vegetation-cutting operating end of FIG. 1. Because this is so, and for 
ease of description and understanding, this is assumed to be the case 
herein. Thus, with respect to the vegetation-cutting operating end in FIG. 
1, FIGS. 4 through 9 represent the embodiment with that operating end. 
However, such figures also represent the embodiment with the earth-working 
operating end of FIG. 2. However, certain differences between those 
components of FIGS. 4 through 9, which may be adopted and exist for the 
two different types of operating ends, as well as variations which might 
typically occur to change the characteristics of the vegetation-cutting or 
earth-working operating end will also be noted. 
For example, FIG. 16A represents a deceleration worm element 136. Rather 
than having a set of six uniform extender threads and retractor threads, 
this worm element, in each case, varies the threads at the end of the set 
to slow the linear motion resulting from the threads where the transitions 
between the extend portion of the cycle and the retract portion of the 
cycle occur. On the other hand, a fast-retract worm element is represented 
in FIG. 16B in which the retractor set of threads number only three while 
the extender set remains six so that six tool shaft rotations are required 
for the extender tooth to move along the set of extender threads, but only 
three rotations are required for the retractor tooth to move along the 
retractor set of threads. 
In FIG. 16C, a fast-retract and variant extender thread worm element is 
represented. Here, the set of retractor threads is as in FIG. 16B. And the 
set of extender thread numbers the same as in FIG. 16B; however, each of 
the extender set of threads has one form for 60 degrees of its 360 degree 
extent and another form for 300 degrees. By way of example, such a 
variation can be adopted to adapt the threads to a power variation from 
the prime mover during the 360 degree rotation cycle of the prime mover--a 
characteristic which is typical of prime movers, particularly of the 
gas-powered variety. 
With respect to differences between the operating end for the earth-working 
tool and for the vegetation-cutting tool, FIG. 14 shows the parts for the 
operating end of the earth-working tool which correspond to the parts of 
FIG. 10 for the operating end of the vegetation-cutting tool. Thus, in 
FIG. 14, there is a cultivator arm 146, a cultivator rocker 150, a 
cultivator yoke 152 and a cultivator mounting piece 154. And FIG. 15 shows 
these components and the components down the drive train therefrom for the 
earth-working operating end. Thus, with reference to the view of FIG. 15, 
there is a left hoeing tine 156, which moves with a left connecting arm 
158, which, thus, both are driven by the yoke 152, 180 degrees 
out-of-phase with a right hoeing tine 160 and a right connecting arm 162. 
A right rocker shaft 164, which can be seen in FIG. 15, to which the right 
connecting arm and right hoeing tine are fixed, rotationally oscillates 
with the movement of the connecting arm and tine, serving as a shaft for 
the movement of the tine and arm, including the pendulum-like oscillation 
of the tine. At the left in FIG. 15, a left rocker shaft cover 166, in 
place, covers most of the left rocker shaft 170. 
Now some of the features already addressed by way of introduction and 
summary, will be described in additional detail, and other related 
features will also be described in detail. 
Turning to FIG. 1, as previously observed, the part of the tool 20 down to 
the operating head end 22 for a vegetation-cutting tool applies both to 
that operating head end and to an operating head end 172, shown in FIG. 2, 
for the earth-working tool. The operator (or power) end of the tool, as 
shown in FIG. 1, has a motor 174, of a fully conventional type at the top, 
a hand grip 180 of a rubber material for one hand of the user, near the 
motor, a throttle lever 178 for the motor, and a handle 180, somewhat 
below the throttle lever, for the other, lower hand of the user. 
Turning to FIG. 3, as is conventional, the throttle lever 180 is pushed to 
cause the engagement of a conventional centrifugal clutch employing a 
clutch drum 182 (with the members which fly out to engage the inside of 
the drum, not shown). A conventional ball bearing is press-fit inside a 
clutch housing 186 (the details of such clutch housing press-fit not 
shown). An arbor 190, which is fixed to and may be integral with the 
clutch drum, is press-fit inside the ball-bearing. A snap-ring (also not 
shown) may be snap-fit about the arbor against the ball-bearing 184, as an 
added precaution to maintain the ball-bearing in its press-fit position. 
As can be readily appreciated, these aspects, as well as the squared-off 
upper end 192 of the tool drive shaft 58 which fits into a square opening 
194 through the arbor, are fully conventional. Of course, it will be 
evident that detailed aspects of this can be readily varied, as 
convenient, without affecting the mode of operation. 
The motor, or engine, as shown, is a gasoline engine. However, an 
electrical motor, also, can readily be employed. One-cylinder, two-cycle, 
air-cooled, recoil starter gasoline engines of the type sold by the 
Mitsubishi Organization are exemplary of the type of conventional engine 
which is fully appropriate. 
The tool 20, whether in its vegetation-cutting tool form as represented in 
FIG. 1 or in its earth-working tool form having the earth-work operating 
end of FIG. 2, as is conventional for tools of this type, has a shaft tube 
196, which serves as a cover for the elongated tool drive shaft 58 and for 
various elements associated with such shaft. Still referring to FIG. 3, 
the tool employs a conventional tubular liner 198 of a plastic material 
about the tool shaft. This liner extends upward to the vicinity of the 
clutch housing 186, near the motor 174. There are then conventional 
spacers, which might be three in number, one of which is shown at 200 (and 
another at 201 in FIG. 4), of a rubber material, along the liner, between 
the liner and the drive shaft tube 196. As is conventional, these spacers 
are distributed along the length of the shaft tube portion of the tool. 
Again, as will be evident, these features are fully conventional. 
As already indicated, FIG. 4 shows a portion of the drive train, for either 
the vegetation-cutting operating end of FIG. 1 or for the earth-working 
operating end of FIG. 2. It shows such portion inside the narrowed, upper 
part 202 of the operating end housing for either operating end. Referring 
to that figure, the elongated tool drive shaft 58 ends in a squared-off 
portion 204 of the shaft which fits into, for purposes of rotational 
coupling, a squared-off receiver socket 206 of the input connector, socket 
member 60, previously referred to. The opposite end of the socket member, 
down the drive train, has an internally threaded opening into which the 
externally threaded, extender end 210 of the worm element is threaded (see 
also FIG. 5). So the tool drive shaft 58 rotates the worm element 74, 
through the input connector, socket member in straight-forward fashion. As 
indicated in FIG. 5 by a rotational direction arrow 214, the tool shaft is 
assumed to rotate clockwise, looking down the drive train for the tool. 
As previously noted, FIGS. 5 through 9, as well as FIG. 4 as just 
discussed, apply equally well to either the vegetation-cutting operating 
end 22 of FIG. 1 or the earth-working operating end 172 of FIG. 2. And 
turning to FIGS. 5 through 9 in additional detail, in the embodiment shown 
in FIG. 5, there are assumed to be six threads in the set of extender 
threads 78 and, also, six threads in the set of retractor threads 80. In 
this regard, as would be expected, each given thread covers a complete 
revolution so that it ends at the same angular position at which it 
starts, but, of course, at a different position along the length of the 
worm element 74. Thus, there is an outside, upper extender thread 216 and 
an outside, lower extender thread 218. And the start, along the worm 
element, of that upper thread defines the starting and ending angular 
position for each of the six threads, including the four intermediate 
extender threads 220. Similarly, with regard to the set of retractor 
threads 80, the angular position of the start and termination for each of 
these six threads, then, is the same as the angular position of the start 
of the outside, lower retractor thread 220. Along the same lines as for 
the extender set of threads, of course, there also is an outside, upper 
retractor thread 222 and four, intermediate retractor threads 224. 
Each of the extender threads 78, as is apparent in FIG. 5, is angled an 
equal angle to each of the other extender threads, and in one direction, 
and each of the retractor threads 80 is angled an angle which is equal to 
that of each of the other retractor threads, and which is in the opposite 
direction as for the extender threads. As would be expected, such angles 
are measured as the angle away from how the thread would be oriented if it 
were oriented perpendicular to the axis of rotation 82 for the worm 
element 74 so as not to push the tooth it would engage, and thus the tooth 
carrier, in either linear direction. Thus, in FIG. 5, the extender threads 
are angled in the direction which acts on the extender tooth 84 carried by 
the tooth carrier 76, to extend the tooth carrier in the linear direction, 
down the drive train, along the tooth carrier axis 94, with the rotation 
of the worm element by the tool shaft 58. And the retractor threads are 
angled such that they act on the retractor tooth 86 carried by the tooth 
carrier, to return the tooth carrier back up the drive train along the 
tooth carrier axis, with such rotation. 
In the transition during the cyclical linear movement of the tooth carrier 
from the extend part of its cycle to the retract part of its cycle, as the 
extender tooth 84 is being pushed along by the outside, lower extender 
thread 218 toward the mid-plane of the worm element 74, the extender ramp 
rider 92 is contacted on its underside by the extender ramp sector 90 (see 
also FIGS. 9A through 9D). This extender ramp sector 90 has a form, which 
to the extender ramp rider 92, appears as a ramp which the ramp rider 
follows as it continues down the worm element along the ramp sector. The 
effect of this is that the form of the ramp sector causes the tooth 
carrier 76 to, with reference to FIG. 5, rotate away from the worm element 
about the axis 94 of the tooth carrier. This, of course, at the same time, 
causes the retractor tooth 86 to rotate with the tooth carrier, toward the 
worm element. After the extender tooth 84 has rotated through an angle 
sufficient to avoid engagement with the extender threads, with the 
retractor tooth 86 rotating a sufficient angle to engage the retractor 
threads, the ramp sector reverses, at that point along the sector, both 
its ramp effect and the direction, along the worm element, which it pushes 
on the extender ramp rider 92. Thus, the extender ramp sector, at that 
point along the worm element, becomes a downward ramp and also pushes the 
ramp rider back off the ramp sector. With this occurring, the retractor 
tooth 86 starts being pushed in the direction up the drive train, after 
hitting against the worm element between the outside, lower retractor 
thread 220 and the intermediate retractor thread next to it. Thus, the 
rotation of the tooth carrier 76 and of the extender tooth 84 stop with 
the extender tooth 84 at a position that it can move back up along the 
worm element without engaging the retractor threads 78. Thus, with the 
retractor tooth 86 engaged and the extender tooth not engaged, the 
continued rotation of the worm element now forces the tooth carrier 76 in 
the direction back up the drive train in the retract part of the cycle. 
The reverse of this, of course, occurs as the retractor tooth 86 approaches 
the retractor ramp sector 96 of the worm element (see also FIGS. 9A 
through 9D). Thus, the retractor tooth becomes disengaged, the extender 
tooth becomes engaged, and the extend part of the cycle begins again. The 
extender ramp sector 90 and the retractor ramp sector 96, of course, in 
keeping with the different angular positions of the extender 84 and 
retractor 86 teeth, are out-of-phase with one another, so far as their 
form with respect to a given angular position on the worm element is 
concerned. But apart from that, their forms are analogous in that they are 
mirror images of one another. Thus, when the worm element 74 is oriented 
so that the start of the extender ramp sector is at one angular position, 
the start of the retractor ramp sector is at a different angular position. 
And when the worm element is oriented so that the position where the 
extender ramp sector reverses to a down hill ramp and acts to push in the 
direction up the drive train rather than down the drive train is at one 
angular position, the position of the retractor ramp where such occurs is 
also at a different angular position. Also, although the ramp sectors are 
designed and formed such that the riding of the ramp rider on the ramp 
sector could be for in the range of 360 degrees of rotation, the actual 
contact of a ramp rider with a ramp sector, during which the ramp rider 
encounters an upward part of the ramp which pushes the ramp rider toward 
the center of the worm element, and then continues along a portion of the 
ramp in which these two effects are reversed, may, more typically, 
approach 90 degrees of rotation or even less. Saying this another way, the 
transition, caused by the ramp sectors, can readily occur over an angle of 
rotation substantially less than 360 degrees. From another, somewhat more 
abstract perspective, each ramp sector may be generally viewed as in the 
nature of a continuation of the threads which lead to it, but with a 
spiral outward and then back inward, and with a reversal in thread angle 
direction occurring with the reversal from outward to inward of the 
spiral. 
The extender catcher 104, the extender catcher projection 106, the 
retractor catcher 100 and the retractor catcher projection 102 are also 
present for purposes of the transitions between the extend and retract 
part of the cycle for the linear movement of the tooth carrier 76. 
Specifically, the extender catcher is formed to have a circular shape and 
to have a circumferential extender catcher flange 222. As can be seen by 
reference to FIGS. 9A through 9D, the extent of the projection provided by 
the flange toward the mid-plane of the worm element, varies with angular 
position on the worm element. Similarly, and related to this, the 
thickness of the base of the extender projection also varies with such 
angular position. Thus, the surface 224 of such base facing toward the 
extender contact projection 106, along a portion thereof, presents an 
annular ramp form to such catcher projection. The purpose of the flange is 
to provide a circumferential barrier for the extender catcher projection 
in transitions from the retract portion of the cycle to the extend portion 
of the cycle. And the purpose of the annular ramp form is to provide a 
similar end barrier for the linear movement of the extender catcher 
projection. Depending on the particular details as to form and 
interaction, along with the particular operational circumstances, 
including loading, the extender catcher projection may or may not contact 
the extender catcher flange or the extender catcher base surface in the 
transition. However, even if such contact does not occur in a particular 
circumstance, the barrier exists and contact may occur if different 
conditions arise at a different time. The ramp form provided by the 
extender base catcher surface, where there is such contact with such 
surface, because of such form, can act as a push-off ramp for the extender 
catcher projection and, thus, aid in accomplishing the change in linear 
direction associated with the transitions from the retract to the extent 
parts of the tooth carrier cycle. 
The retractor catcher 100 has a form which would be the mirror image of the 
extender catcher 104, except, of course, it has a different angular 
disposition on the worm element 74, to provide an analogous barrier for 
the retractor catcher projection 102 in transitions from the extend part 
of the cycle to the retract part of the cycle. The circumferential 
retractor catcher flange 226, and the retractor catcher base surface 230, 
presenting an annular ramp form to the retractor catcher projection, which 
are analogous to the corresponding elements for the extender catcher 104, 
can be readily seen in FIGS. 9A through 9D. 
Although such, of course, can vary, where there is contact between a 
catcher projection and a catcher flange or catcher base surface presenting 
the ramp form, the angle of rotation through which such contact might 
occur could, for example, most typically, be in the range of 90 degrees or 
less. As indicated, however, that can substantially vary. 
The mounting of the worm element 74 and of the tooth carrier 76 in the 
housing 64 for such components, and the interaction of an extender guide 
projection 230, projecting from the extender tooth 84, and of a retractor 
guide projection 232, projecting from the retractor tooth 102, with parts 
of the housing, can be appreciated by reference to FIGS. 5, 7A and B and 
8A, B and C. The front half 66 (with reference to the view of FIG. 4) of 
the housing is formed to provide half of each bearing surface for the 
rotation of the worm element and for the linear movement, as well as the 
rotational movement through an angle in accomplishing the cyclical 
transitions, of the tooth carrier 76. Thus, the front half 66 of the 
housing has a lower (with reference to the direction of the drive train in 
FIG. 4) worm element bearing surface 234 which cooperates with a lower 
worm element bearing surface 236 of the back half 70 of the housing. They 
together form a circular-shaped bearing surface about the retractor end of 
the worm element. There are then analogous upper worm element bearing 
surfaces 238 and 240 of the front and back halves of the housing, 
respectively, for the extender end of the worm element, which provide the 
same function at that end. Similarly, lower tooth carrier bearing surfaces 
242 and 244 of the front and back halves of the housing, respectively, 
cooperate to provide a circular-shaped bearing surface for the tooth 
carrier 76 along the retractor-tooth end of the carrier. Similarly, upper 
tooth carrier bearing surfaces 246 and 250 of the front and back halves of 
the housing, respectively, cooperate to provide a circular-shaped bearing 
surface along the extender-end of the tooth carrier. 
An upper thrust bearing 252 fits about the extender end 212 of the worm 
element. It is mounted between an upper, outer 254 and upper, inner 256 
thrust washer. These, of course, are conventional parts used in 
conventional ways. An upper thrust cavity, then, is formed by the worm 
element, tooth carrier and related component housing 64, for these upper 
thrust components. The cavity, which is formed specifically for such 
components, is provided by the cooperating upper thrust component cavities 
258 and 260 in the front 66 and back 70 housing halves, respectively. 
There then is an analogous lower thrust bearing 262 about the retractor 
end 264 of the worm element, a lower, outer thrust washer 266 and a lower, 
inner thrust washer 268. And lower thrust component cavities 269 and 270 
of the front 66 and back 70 halves of the housing, cooperate to form a 
housing cavity for the lower thrust components. 
Referring back to the retractor guide projection 232, the track sector 72 
of the back half 70 of the housing 64 for the worm element, tooth carrier 
and related components, has a form which provides guiding structure for 
the retractor guide projection during the linear movement of the tooth 
carrier 76 and, thus, provides a guiding function for the tooth carrier 76 
itself. There also is an analogous track sector 272 of the front half 66 
of the housing which interacts analogously with the extender guide 
projection 230. Specifically, and referring to the back housing half, 
track sector 72, that sector has a central wall 274 and an outer wall 276. 
There is then in the nature of an elongated, generally oval-shaped channel 
between such walls having an extend portion 278, a retract portion 280, a 
retract-to-extend transition portion 282 and an extend-to-retract 
transition portion 284. The spacial relationship of the back half of the 
housing and of the retractor guide projection 232 on the retractor tooth 
86, then, is such that the retractor guide projection moves along the 
extend portion 278 of the channel as the tooth carrier extends in its 
linear direction down the drive train. In the transition from that extend 
part of the cycle to the retract part of the cycle, the retractor guide 
projection 232 moves through the extend-to-retract transition portion 284 
of the channel into the retract portion 280 of the channel. And, then, 
during the retract part of the cycle, the retractor guide projection moves 
along the retract portion of the channel. In the transition back to the 
extend part of the cycle again, the guide projection moves through the 
retract-to-extend transition portion 282 of the channel back to the extend 
portion of the channel. 
The relationship and interaction between the extender guide projection 230 
and the track sector 272 of the front half 66 of the housing 64 is 
analogous. Thus, that track sector 272 also has a central wall 286, an 
outer wall 290 and a channel between such walls. The channel has an extend 
portion 292, a retract portion 294, an extend-to-retract transition 
portion 296 and a retract-to-extend transition portion 298. The extender 
guide projection 230, then, as the tooth carrier 276 extends down the 
drive train, moves along the extend portion of the channel. In the 
transition from the extend part of the cycle for the tooth carrier to the 
retract part, the extender guide projection moves through the 
extend-to-retract portion 296 of the channel, to the retract portion of 
the channel. It, then, during the retract part of the tooth carrier cycle, 
moves along the retract portion of the channel, and returns to the extend 
portion, through the retract-to-extend transition portion 298, in the 
transition back to the extend part of the tooth carrier cycle. 
The guide projections 230 and 232, along with the track sectors 72 and 272 
may generally be considered to be in the nature of an extra, redundant 
protection. Specifically, the encountering of the worm element 74 by the 
extender 84 and retractor 86 teeth during operation is designed to define 
and limit the back-and-forth rotation of the tooth carrier 76 during its 
cyclical movement. However, the walls of the track sectors 72 and 272 are 
also present to limit such movement and to provide additional strength 
against forces which may be exerted by the teeth during the operation of 
the device. Thus, the guide projections 230 and 232, along with the track 
sectors 72 and 272 may be designed so that there is, in fact, guide 
projection-wall contact during normal operation--i.e., such that the walls 
can provide added strength in normal operation. On the other hand, the 
design can be such that guide projection-track sector wall contact during 
normal operation generally does not occur or is not expected, but that 
such contact generally occurs or is expected only during more extreme 
circumstances. 
The walls of the track sectors 72 and 272, as shown in FIGS. 7 and 8 are of 
the same material, and integrally formed with, the remainder of the halves 
of the housing 64 for the worm element, tooth carrier and related 
components. One material which is particularly advantageous is a zinc 
alloy sold by a variety of manufacturers under the designation ZA8. This 
is a self-lubricating alloy. Such a self-lubricating alloy is particularly 
advantageous where, as in the embodiment shown, the housing material 
provides bearing surfaces for the worm element 74 and tooth carrier 76. 
However, with respect to the track sectors, for purposes of added 
strength, lengths of a stronger material, such as a steel material, can be 
disposed within wall portions of the track sector and molded into 
surrounding material of the housing halves. As indicated, this is an 
alternative for added strength along such wall portions. 
Referring to FIGS. 7 and 8, the back half 70 of the housing 64 has four 
internally-threaded screw holes 300 therethrough and the front half 66 has 
four respectively cooperating unthreaded screw holes 302 therethrough. 
Each of four connector screws 304 then extends through such a screw hole 
302 of the front housing half and is threaded into a corresponding screw 
hole 300 of the back housing half (FIG. 4). As shown in FIGS. 7A and 7B, 
these screws can be counter-sunk below the outer surface of the front 
housing half. 
The operation and interaction of the case-minus-carrier spring 116, the 
spring stop 114, the carrier-minus-case spring 110 and the spring case 
112, with the cyclical linear movement of the tooth carrier 76, has 
already been described in some degree of detail. Thus, it has already been 
noted how such elements act as in the nature of a clutching, and 
shock-absorbing or shock damping, mechanism. Thus, the case-minus-carrier 
spring 116 compresses with respect to its normal, at-rest state in the 
spring case 112, when the difference in the positions, down the drive 
train, of the case 112 and the tooth carrier 76, becomes less than the 
normal, at-rest state difference. This spring, then, expands from its 
at-rest state, when such difference becomes greater than the at-rest state 
difference. On the other hand, the carrier-minus-case spring becomes 
compressed from its normal, at-rest state in the spring case, when the 
difference in position, down the drive train, of the case 112 and the 
tooth carrier 76 becomes greater than the normal at-rest state difference. 
And this spring expands from its at-rest state, when such difference in 
positions become less than the normal, at rest state difference. As is 
apparent from this description, and from FIG. 5, this difference can be 
viewed with respect to the ends of the case 112 and tooth carrier 76 which 
are at the down-drive train ends of such components. 
The springs 116 and 110 can be standard springs made of standard spring 
steel. On the other hand, if specially made, including specially tempered 
and wound to desired specifications, the design could incorporate springs 
which are very short--such as of the order of one-half inch or less. It is 
desirable that the springs, which are identical, have a spring constant 
which is sufficiently large to essentially avoid compression or expansion, 
from their normal at-rest state in the case 112, over a substantial range 
of operation by the tool. Where that exists, the springs essentially act 
merely to transfer power and not in a clutching, or shock-absorbing or 
damping, fashion The springs, of course, also, have to be able to cycle at 
the rate of the cycling for the tooth carrier. Simply by way of example, 
for the earth-working operating end 172 (FIG. 2), the springs might start 
to compress and expand from their normal, at-rest state when the tool 
reaches an unloaded rate of cyclical hoeing tine movement (and thus tooth 
carrier movement) of 2,500 cycles per minute. The springs might then, when 
that rate reaches 3,500 cycles per minute, cycle between their 
fully-compressed and fully expanded states, and, essentially stop the 
transfer of any meaningful power down the drive train. As indicated, these 
exemplary characteristics are set forth for an unloaded state at the 
operating end. However, the loading at the operating end, of course, is a 
variable which affects when the springs begin to compress and expand from 
their normal, at-rest states and reach a situation when, during the cycle 
of back-and-forth movement of the tooth carrier 76, they reach fully 
compressed and expanded operation. Thus, for example, encountering a 
large, immovable rock, which without the spring-related mechanism, might 
severely damage the drive train, with the spring-related mechanism, may 
well not cause significant damage. 
With respect to the vegetation-cutting operating end 22 (FIG. 1), by way of 
example, the onset of compression and expansion from the normal, at-rest 
states of the springs in the case might be at 1,500 cycles per second, 
unloaded, with full compression at 2,000 cycles, unloaded. Again, the 
loading is another variable which will affect this and the example of an 
immovable rock, just noted for the earth-working operating end, of course, 
also applies here. These numbers, as well as those for the earth-working 
operating end, as indicated, are merely illustrative. And potential 
variations can readily be adopted in implementing the specific 
characteristics desired for a particular tool form. 
Turning back to the worm element 74, tooth carrier 76, and related 
components, the worm element and catchers 100 and 104 can be integrally 
formed of a standard hardened and tempered steel material such as that 
supplied by various manufacturers under the designation 4140. The tooth 
carrier 76, teeth 84 and 86, ramp riders 92 and 98, catcher projections 
102 and 106 and guide projections 230 and 232, can also be integrally 
formed of the same material. However, for ease of formation, each tooth 
and the ramp rider, catcher projection and guide projection therein can be 
integrally formed and then rigidly screwed in position onto the tooth 
carrier 76. Of course a variety of conventional alternatives, both as to 
the fabrication and the material, can readily be employed. 
The structure and operation of the vegetation-cutting apparatus, down the 
drive train from the parts that have already been focused upon, is readily 
understood from FIGS. 10-13 and the description applicable thereto which 
has already been given. The same can be said for the structure and 
operation of the components of the earth-working tool shown in FIGS. 14 
and 15. Nevertheless, in both cases, some additional description is 
appropriate. 
Referring to FIG. 10, and to some extent back to FIG. 5, the spring case 
112 at its end down the drive train is connected to the reciprocator arm 
118. This connection is through a bolt 306 which is mounted so that its 
barrel passes through an opening 310 defined at the very tip of the spring 
case. This connector bolt 306 is firmly connected by a nut 311 so that its 
barrel passes not only through the spring case connector opening 310 but 
through an elongated opening 312 formed by the upper end structure of the 
reciprocator arm 318. Of course, a variety of alternative standard 
connectors can be used apart from the bolt and nut, which would present 
the appropriate cylindrical barrel structure through the spring case 
connector opening and the elongated reciprocator arm opening. The 
reciprocator arm 118, then, along a lower leg thereof, passes through an 
arm opening 313 of the reciprocator rocker 120. That arm opening, downward 
through rocker, as shown in FIG. 10, runs in a direction perpendicular to 
the axis of the rocker. 
The reciprocator arm 18 has upper 314, middle 316 and lower 318 openings 
therethrough at positions along the length of the lower leg of that arm. 
The arm is held by the rocker by disposing that leg through the arm 
opening 312 of the rocker and passing a rocker bolt 320 through an opening 
along the axis of the rocker and through the desired upper, middle or 
lower arm opening. The bolt 320 is held firmly in position by screwing it 
into the internally threaded axial rocker opening. 
The choice of the opening through the reciprocator arm for the connection 
to the rocker 120, of course, adjusts the extent of the back-and-forth 
linear movement of the reciprocator yoke 122 with the back-and-forth 
linear movement of the spring case 112. As is apparent, this, also, then 
adjusts the back-and-forth angle for the rotational oscillation of the 
blades of the vegetation-cutting operating end 22. 
The reciprocator arm 118, at its lower end, has structure providing a 
lower, elongated arm opening 324. A connector pin 326, having threads on 
both ends, is then connected to the yoke 122 so that the barrel of the pin 
is disposed between a pair of ears 330, having openings for the pin, which 
are formed on the yoke. A pair of nuts 332 are used for this connection. 
Of course, other conventional arrangements, providing a barrel could 
readily be employed. The barrel of the pin 326, then, also passes through 
the lower elongated arm opening 324. 
The yoke 122 is slidably mounted in the reciprocator mounting piece 124. A 
pair of mounting flanges 334, extending along the underside of the 
mounting piece 124 are used in maintaining the slidable mounting of the 
yoke 122. The reciprocator arm 118, the rocker 120, the mounting piece 124 
and the yoke 122 can conveniently be made of a steel material, for 
example, the material sold by a variety of manufactures under the general 
designation 4140. Of course, however, this is merely one of many possible 
examples. 
Continuing down the drive train, a portion of the reciprocator yoke 122 
also appears in FIG. 11. Referring to that figure, the yoke has a 
generally cross-shaped opening 336 having a central portion 338, a link 
pin portion 340 and a blade pin portion 342. The link pin 130 projecting 
from the link 132, during the operation of the mechanism, fits in the link 
pin portion of the opening and moves back-and-forth along the opening. 
Similarly, the upper blade pin 126 projecting from the upper blade 24 fits 
in the blade pin portion 342 of the opening, moving back-and-forth along 
that portion of the opening. Of course, those two portions of the opening 
are formed to just fit about such pins so as to essentially limit their 
movement to slidable movement along their lengths as the yoke 122 moves 
linearly back-and-forth. 
During this movement of the yoke, the outer casing 344 for a needle bearing 
346 is disposed along the central portion 338 of the yoke opening. That 
central portion is formed to fit closely about the bearing casing at the 
ends of such portion as the portion moves back-and-forth along the casing. 
Thus, both that portion of the opening and the slidable mounting of the 
yoke in the reciprocator mounting piece 124 restrict the yoke against 
sideways movement. 
Referring to FIGS. 11, 12 and 13B, the needle bearing 346 is press-fit 
along its casing 344 through the center of the upper blade 24. Then the 
lower blade shaft 134 rotates inside the bearing 346 with the movement of 
the link pin 130. More specifically, the link pin 130 causes the link 132 
to rotationally oscillate about the axis of the shaft. The shaft extends 
between the forked portion of the link, between wall structure of that 
portion formed to fit about the shaft. The shaft, also, has mounted 
thereon, projecting therefrom, an upper shaft pin 350 which fits between a 
narrow portion of the opening between the forked portion of the link. This 
and the fit of the fork portion about the shaft cause the shaft to 
rotationally oscillate with the movement of the link. A link screw 352 
passes through one leg of the fork and is screwed into the other leg to 
assure the tightness of the fit about the shaft 134. 
A lower shaft pin 352, extending through the shaft, couples the shaft to 
the lower blade 26 by extending, at each of its ends, into the elongated 
ends 354 of an opening 356 extending a small distance upward from the 
bottom of the lower blade 26. The opening, of course, is at the center of 
the blade along the thickest part of the blade structure. 
The lower blade structure 26 substantially increases in thickness toward 
its center and then increases even more yet closer to the center. Although 
in the embodiment shown, this blade structure is integral, these thickened 
portions, alternatively, can readily be formed by separate pieces mounted 
on a separate blade--one piece to add the first degree of added thickness 
and another piece to add the additional degree of thickness The portion 
having the initial degree of added thickness is shown at 358 in FIGS. 12 
and 13B and the portion having still greater thickness is shown at 360. 
The analogous situation applies for a central portion 362 of the upper 
blade 24 having substantial added thickness (see FIG. 13A). In fact, in 
the particular embodiment, the underside of the reciprocator mounting 
piece 124 rests on that thickened portion 362 as that portion oscillates 
back-and-forth under and against such underside. Of course, it will be 
evident that other, alternative arrangements can also be adopted. 
Although the upper 24 and lower 26 blades have three different forms of 
teeth, such blades, of course, could simply have a single form, or more 
than three forms. Where a single form is used, most typically that form 
would be a form adapted for low difficulty vegetation. However, the pair 
of blades having that single tooth form could be replaced with a pair 
having a single, second tooth form or a pair having a single, third tooth 
form, et cetera. In the particular embodiments of FIG. 13, there are 
eleven tooth ends in the high difficulty sets of teeth 38 and 52 and five 
tooth ends in the intermediate difficulty sets of teeth 34 and 46. In the 
blade embodiments 24 and 26 shown, and which will typically be the case, 
the tooth structures slope slightly toward one another when the blades are 
assembled in their face-to-face position. Similarly, the portions of the 
blades other than the just-referenced central thickened portions also 
slope toward one another, such sloped portions thus presenting a somewhat 
concave shape toward the space between the assembled blades. In operation, 
the blades might typically oscillate back-and-forth through about 30 
degrees of rotation; however, variations for this, depending on the 
particular desired design characteristics for the vegetation cutting tool, 
between about ten degrees and 90 degrees might be expected. 
Returning to FIG. 12, there is a sleeve 366 that acts as a spacer below the 
needle bearing 346 that is mounted in the upper blade 24, and above the 
lower blade 26. And above the link 132, there is another sleeve 370 about 
the lower blade shaft 134 to the inside of an upper needle bearing 372. 
The lower shaft 134 fits through an opening 374 through a shelf 376 of the 
mounting piece 124 (FIG. 10). The upper needle bearing is press-fit in 
that shelf opening and the upper sleeve is between the bearing and the 
shaft. The sleeve, of course, could readily be eliminated, with the shaft 
directly against a smaller-size needle bearing. A retainer piece 378 (of 
the snap-on type having a circumferential gap) fits in a groove along the 
outside of the shaft 134, against the top of the upper sleeve 370 and the 
inside portion of the upper needle bearing 372 to help hold the shaft in 
position. 
Referring to FIG. 14, the cultivator mounting piece 154 has a somewhat 
different form than the reciprocator mounting piece 124. But its function 
and interaction with the cultivator arm 146, cultivator rocker 150, and 
upper 380, middle 382 and lower 384 openings through the lower leg of the 
cultivator arm are fully analogous to what was described for the 
vegetation-cutting operating end. And the same applies to the following 
elements of the earth-working operating end, which have comparable 
elements with respect to the vegetation-cutting operating end: the bolt 
386 for the cultivator rocker 150, threaded into an internally-threaded 
axial rocker opening; the ears 386 projecting from the cultivator yoke 
152; and the pin 390, threaded on either end, to connect the lower end of 
the reciprocator arm to the reciprocator yoke. Also, the elongated opening 
394 through the lower end of the cultivator arm 146, functions as a 
connector opening at the lower end of the arm in the same manner as the 
comparable opening through the lower end of the reciprocator arm 118. 
The rear part of the cultivator yoke 152, fits above mounting flanges 396 
along the lower portion of the cultivator mounting piece 154. And, as with 
the situation for the vegetation-cutting operating end, the cultivator 
yoke 152 is confined to linear, back-and-forth movement by the mounting 
piece 154. However, because of the nature of the earth-working operating 
end, the front portion of the cultivator yoke 152 is formed differently 
then the front portion of the reciprocator yoke 122. 
Specifically, the front portion first narrows and then extends vertically 
through the continuation of the centerline of the back portion to provide, 
with reference to the direction of FIG. 14, an upper elongated opening 396 
and a lower elongated opening 398. When in position, as in FIG. 15, the 
elongation direction for these openings is generally along the length of 
the housing for the earth-working operating end (as in FIG. 15). The 
cyclical, back-and-forth movement of the cultivator yoke 152 thus causes 
the pendulum-like oscillation of the left 156 and right 160 hoeing tines 
through the left 158 and right 162 connector arms, respectively, which are 
attached to the inner ends of the left 166 and right 164 rocker shafts, 
respectively. The oscillation of the two connector arms and, thus, of the 
two hoeing tines, of course, are directly, i.e., 180 degrees, out-of-phase 
with one another. Although the connector arms are shown extending through 
their respective yoke openings without any bushings about such arms in the 
openings, of course, the use of bushings could, alternatively, readily be 
adopted. The size of the elongated yoke openings 396 and 398 for the 
connector arms is closely matched to the size of the circular-shaped legs 
of the connector arms which extend through such openings, to essentially 
confine those arms to, with respect to their respective yoke openings, 
movement back-and-forth along the openings. In the embodiment shown in 
FIG. 15, the cultivator mounting piece 154 is mounted in the operating end 
housing, in conventional fashion (mounting components for such not shown). 
This can be accomplished through brackets, through a base structure below 
the mounting piece or through a variety of other conventional methods. 
The tines 156 and 160 are of a type which are now conventional. The way of 
fixing them in position, the rocker shafts 164 and 166, and the way of 
mounting such rocker shafts, are all, also, conventional. And, as is 
apparent, the parts and description for the left side are analogous to 
those for the right side. Thus, referring to the right side, there is an 
inner 396 and an outer 398 bushing about the rocker shaft mounted in the 
housing. The outer bushing fits into a cavity of a right tine mounting 
piece 399. A tine retainer piece 400 is tightly against the outside 
surface of the tine between small flanges projecting from such surface. 
And a bolt 402 and pair of nuts 404 are used in fixing the tine in 
position. An O-ring 406 is fitted in the housing against the tine mounting 
piece 399. And a retainer piece 407 (of the snap-on type having a 
circumferential gap) helps hold the right rocker shaft 164 in position. As 
shown at the left, where the rocker shaft cover 166, is in place, there is 
a cover for each of the rocker shafts. Thus, each rocker shaft 
rotationally oscillates back-and-forth with its respective tine and 
connector arm. 
Referring back to FIG. 5, as already noted, the extender set of threads 78 
and the retractor set of treads 80 each have six threads. And in that 
embodiment, the pitch spacing, the distance between adjacent threads along 
the length of the worm element, is uniform along each set of threads, and 
also the same for the two sets of threads. Also, the pitch angle, the 
angle measured as the angle away from how the thread would be oriented if 
it were oriented perpendicular to the axis of rotation 82 for the worm 
element 74 so as not to push the tooth it would engage, and thus the tooth 
carrier, in either linear direction, is uniform along each set and of the 
same size, but opposite in direction, for the extender set and the 
retractor set. In other embodiments, by way of example, one might find 
that certain minimal variations associated with the thread adjacent the 
respective ramp sector 90 or 96 may be useful to permit the applicable 
tooth 84 or 86 additional room to maneuver with respect to the transitions 
relating to the ramp riders 92 and 86 and the ramp sectors. 
In addition, in the embodiments shown, the worm element: and related 
components are the same for the vegetation-cutting operating end 22 and 
for the earth-working operating end 172. However, there can be many 
variations, in accordance with differences which may be desired in design 
characteristics. Also, there can be many variations for the same general 
type of apparatus, e.g., vegetation-cutting or earth-working, depending on 
the characteristics desired. By way of example, for an engine which 
typically operates at in the range of 10,000 revolutions per minute, 
unloaded and in the range of 7,500 revolutions per minute loaded, and for 
a vegetation-cutting operating end of the type shown in FIG. 1, having a 
desired normal blade operating rate of 800 to 1,200 cycles per minute, one 
might elect to adopt a worm element having a total number of threads in 
the range of six to ten, with in the range of three to five extender 
threads and three to five retractor threads. On the other hand, for the 
same engine, but for an earth-working operating end having certain 
specific characteristics, one might decide on a total of four threads with 
two in each set. In any case, it is readily apparent that the number of 
threads, in effect, can be used to change the gear reduction ratio between 
the speed of the engine and the speed of the blades or tines. 
On the other hand, if one wanted to maintain the same worm element but 
change the effective gear reduction, one could, for example, employ a 
tooth carrier having two separated extender teeth along the tooth carrier 
and two separated retractor teeth. The respective extender or retractor 
tooth on the outside would then carry the catcher projection and the one 
on the inside would carry the ramp rider. In that case, during the extend 
part of the cycle and the retract part of the cycle, an extender or 
retractor tooth would not have to move through all of the retractor or 
extender threads before a transition to the opposite part of the cycle 
occurred. Thus, there clearly are alternatives to changing worm elements 
in the event a different effective gear reduction ratio is desired. 
Related to what has just been discussed, the fast retract worm element 138, 
schematically represented in FIG. 16B through the worm element portions 
having the threads, but with the ramp sectors and ends of the worm element 
omitted, has six extender threads based on one pitch spacing and pitch 
angle and three retractor threads based on a greater pitch spacing and 
greater (and opposite) pitch angle. The idea there, as is evident from the 
above discussion of this, is to have one effective gear reduction ratio 
for the extend part of the cycle and half the gear reduction ratio for the 
retract part of the cycle. Thus, for example, for the earth-working 
operating end, the tines would return in the retract part of the cycle at 
twice the speed as in the extend part. 
For the fast retract and variant extender thread worm element 140, 
similarly schematically represented in FIG. 16C, the retract aspect is the 
same as for the worm element of 16B. Also, the difference in the gear 
reduction for the extend and retract parts of the cycle is the same as 
described for 16B as there are still six extend threads. However, the 
pitch angle along a 60-degree portion of each of the extend threads is 
greater than for a 300-degree portion of each thread. By way of example, 
this 60-degree portion (which is continuous) may correspond to the portion 
of the engine cycle in which the power output of the engine is greatest. 
Other variations, along these general lines, of course can be made for 
various desired characteristics and operating properties. 
In the deceleration worm element 136, similarly schematically represented 
in FIG. 16A, the pitch angle design applicable to several threads at the 
end of each set of threads is less than the pitch angle design applicable 
to the threads in between. That, of course, is to provide deceleration for 
the movement of the tooth carrier near the points of transition between 
the extend and retract parts of its cycle. By selecting the amount of the 
change in the pitch angle, this can be designed without a change in a 
desired average pitch angle over each set of threads. For example, if one 
desires eight threads with an average pitch angle, one could select eight 
threads having a uniform pitch angle, or, alternatively, have eight 
threads, not all having the same pitch angle but having the same average 
pitch angle for the set as a whole. 
It has already been emphasized that many changes and variations can be made 
in the details of the embodiments that have been described, in accordance 
with the various aspects of the invention. Simply by way of additional 
example, the guide projections 230 and 232, on the teeth carried by the 
tooth carrier, could be replaced by alternative guide projections 
positioned differently and shaped differently, with corresponding changes 
in the tract sectors 72 and 272 of the halves of the housing 64 for the 
worm element 74 and related components. Even more substantially, such 
guide projections could be replaced by alternative guide projections 
mounted directly on the tooth carrier rather than on the pair of teeth 
which are carried by the tooth carrier. Also, it might be observed that 
the tool 22 of FIG. 1, and the blades 22 and 24 thereof, can be used for 
cutting a variety of matter other than vegetation. 
It, thus, will be appreciated by those skilled in the art that many changes 
and variations may be made, as to detail, in the embodiments which have 
been described, without departing from the spirit or scope of the 
invention.