Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to frame shaft and drive
shaft assemblies, and more specifically, to a combined
curved frame shaft and sheath for a flexible drive shaft,
for use in low horsepower implements such as lawn trimming
tools, brush cutters, and the like, in which the shaft
assembly is bent to dispose its tool end at an angle to
its power input end and power is transmitted through the
. -assembly by a flexible drive shaft.
Various low-horsepower manual implements such as
lawn edgers, brush cutters, and ~he like are available on
.~ the market, in which a tubular frame shaft connects a power
head at its upper end to a driven tool at its lower end and
in which power is transmitted from the head to the tool by
a rotating shaft extending through the frame shaft. When
. such implements carry a rotating cutter or other tool, it
~ is desirable to dispose the tool axis of rotation at an
;: anyle to the axis of the power head and upper portion of :
i; the frame shaft, in order to permit the implement to be
~ carried comfortably by an operator in an erect standing or
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. 20 walking position. Such angular relationship has been pro-
vided by bending the lower portion of the frame shaft through
a suitable arc, and by transmitting power from the power
head to the tool by means of a flexible drive shaft con~
tai.ned in a flexible sheath extending through the frame
-~ shaft. Commonly, such sheath is formed of a helically wound
.. tape. The sheath has been held generally concentric with
`~ the Erame shaft by a series of spaced annular bushings.
:- - This arrangement has not been entirely satisfac-
tory. In particular, the flexible sheath does not suffi-
: 30 ciently hold the flexible dr.ive shaEt agains-t distortion and, .
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whipping, which produces vibration and wear. Under some
circums-tances, ~he flexible sheath for the drive shaft will
fail, so that it becomes unwound or enlarged and no longer
constrains the drive shaft ~or rotation on its axis. This
results in failure of that shaft and hence of the implement
- as a whole. The configuration of the shaft assembly, with
; a long straight portion and adjoining arcuate portion, has
heretofore required the use of a fle~ible sheath and pre-
vented the use of a rigid sheath.
The present invention overcomes the problems and
disadvantages o~ the prior art and provides a shaft assembly
... of the desired bent configuration in which the rotating
flexible drive shaft is firmly and closely supported through-
out its length by a rigid sheath.
: In accordance with the invention, a combined
, curved frame shaft and casing or sheath for a flexible drive
shaft is formed by, first, assembling onto a straight length
- of rigid sheath tubing a thick-walled cylindrical bushing of
semirigid material over the length o~ the sheath which is
9ubsequently bent, together with spacer bushings at the ends
of the sheath tube and at spaced points along the length of
the sheath which is to remain straight; second, inserting
such sheath tube assembly in a straight length of frame-
shaEt tube; and third, subjecting the resulting assembly of
sheath tube and frame shaft tube to a bending operation, as
in conventional tube-bending apparatus. In such operation,
the bending action is.applied to the outer frame shaft tube
and the semirigid bushing transm.its the bending action to
the sheath tube contained therein.
The semirigid bushing is desirably an extruded
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length of plastic material, such as polyvinyl chloride
polymer, and any of various known materlals may be used to
provide a bushing of sufficient stiffness to support the
sheath during bending but of sufficient flexibility to per-
mit the desired bending. The spacer bushings may be of any
desired material, and I have found it convenient to use
molded bushings of powdered iron.
It is of course necessary that the bushings remain
in their desired positions both during the assembly and
bending steps and in the completed assembled product.
Desirably, the bushings may be held in place for manufactur-
ing purposes by securing them to the sheath tube with adhe-
` sive tape and by flaring the ends of the sheath tube. After
the bending step has been completed, the elongated thick-
walled bushing will extend about the bend and will be secured
by contact with the walls of the tubes. It will then also
serve to hold adjacent spacer bushings in place. Other
spacer bushings are desirably locked in place by suitable
attachments or deformations of the outer frame shaft tube.
One such spacer bushing is desirably positioned adjacent
the midpoint of the shaft assembly and secured in place by
a grease fitting threaded through the outer frame tube into
the spacer bushing and connected to the interior o~ the
sheath tube.
The frame shaft and sheath tube assembly produced
~ as described above will comprise a ri~id outer tubular frame
;- shaft extending from a head end to a tool end and including
a curved portion. Such fxame shaft will con-tain a she~th
tube of rigid tubing matexial, such as steel or other metal,
extending tbrough the tubular frame shaft and held concentxic
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~ therewith by the elongated semirigid bushing over the bent :
portion of the frame shaft and by the spacer bushings at its
ends and at one or more spaced points along the length of
the straight portion of the frame shaft. Since the sheath
tube is itself rigid, few such spacer bushings are needed,
and are desirably used only at the ends of the straight
''! section. The bushings and tubes are so interconnected that
the parts are all held in predetermined relationship for
use. In use, a flexible drive shaft is inserted in the
sheath tu~e and the shaf~ assembly is provided with a power
head at its uppex end and a tool fitting at its lower end.
The flexible drive shat operativPly connects the power head
to the tool, and is rigidly supported throughout its inter-
vening length by the rigid sheath tube and for rotation on
its axis in such supporting sheath tube.
Thus, in accordance with the present teachings,
a shaft assembly for physically connecting a driving head at
; one end to a driven tool at the other end and for housing a
flexible drive shaft to drive the tool from the head is provided.
The assembly has a straight portion and a bent portion so as to
dispose the axis of the tool end at an angle to the axis of the
driving head. The assembly comprises an outer frame sha~t tube
of relatively large diameter and structural strength which
extends continuously along the straight poxtion and the bent
` portion. An inner sheath tube is provided of relatively much
` smaller diameter formed of rigid but bendable tubing and extend-
ing substantially coaxially through the straight and bent
` portions of the frame shaft. Bushing means is provided interposed
between the two tubes in closely interfitting relation with
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`~oth an including an elongated, -thick-wal.led continuous bushing
of semiri.gid matexiaL exten,.:~ing over the Lengt.h of the bent
: portion of the assembly so as to provide substantially continuous
support for the sheath tube from ~he frame shaft or the bent
portion with means provided in an adjoining straight portion of
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the assembly for holding the sheath tube coaxial with the frame
.. tube.
In accordance with a further embodiment, a method
:; is provided of making a shaft assembly which comprises a rigid
. elongated frame tube for physically connecting a driving head
at one end to a driven tool at the other end. The tube is ~ent
so as to dispose the driven tool on an axis at an angle to the
axis of the driving head and bendable rigid sheath tube of sub-
stantially smaller diameter than the frame tube is p.rovided ex-
tending generally concentrically through the.bent frame tube for
closely containing the flexi~le drive shaft for drivingly
connecting the driving head to the driven tool. The method
provided comprises assembling onto a straight length.of bendable
sheath tube an elongated, thick-walled tubular continuous bushing ~.
of semirigid material, the bushing closely surrounding the sheath
tube and extending along the length of the sheath to which is
later to be bent. Inserting the resulting subassembly, together
with a spacer bushing at each end of the sheath tube, in an :.
enclosing outer shaft tube extending of the whole length of
~ suc~ subassembly and closely surrounding the spacer bushing
- and continuous bushing. Subjecting the resulting final assembly
: of shaft tube and subassembly to a bending operation so as to :.
bend the shaft tube over a length of the assembly in which the
sheath tube is surrounded by the continuous semirigid bushing
thereby causing the semirigid bushing to transmit bending force
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li86
to the sheath tube while maintaining the sheath tube substantially
concentric with the shaft tube over the bent length thereof and
leaving the semirigid bushing in place in the bent assembly to
support the sheath tube in use.
The accompanying drawings illustrate the inven-
tion. In such drawings:
Fig. 1 is a perspective view of a weed cutting
implement having a shaft assembly in accordance with this
invention;
Fig. 2 is a longitudinal section of a subassembly
showing a first stage of assembly in accordance with the
invention;
Fig. 3 is a longitudinal section showing a second
stage o~ assembly;
- Fig. 4 is a longitudinal section showing a com-
pleted shaft assembly in accordance with the invention;
Fig. 5 is an enlarged vertical section taken on
the line 5-5 of Fig. 4;
~ ig. 6 is an enlarged vertical section taken on
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the line 6-6 o E Fig . 4;
Fig. 7 is a longitudinal section showing connection
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of the shaft assembly to a power head;
Fig. 8 is a longitudinal section showing connection
of the shaft assembly to a tool;
Fig. 9 is a section like Fig. 5 but showing a -
modif led semirigid bushing i
- Fig. 10 is a longitudinal sectional view of a
modified fraine shaft and lower end assembly; and
FigO 11 iS an enlarged exploded view showing the
me thod of mounting the arbor shaft for the cutter head in
~; the lower end of the frame tube in the modification of Fig.
10. ...
The implement shown in Fig. 1 is a lawn trim~rer, and is ;
representative of implements in which shaft assemblies in
accordance with the present invention are especially useful.
Such lawn triminer comprises a shaft assembly 10 having a
gasoline engine 12 as its power head at the upper end of such
assenbly 10, and a ro tating lawn cutting tool 14 at the lower
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20 end oE such assembly 10. Shaft assembly 10 is fitted with
handles 16 and 18 by which the implement may be carried and
may be provided with a strap 20 by which it may be hung from
- the shoulders of the operator. The handle 1~ carries a
~ throttle lever 22 for controlling the power head 12. The
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:, shaft assembl~ 10 comprises a long straight upper portion 24
which is coaxial with the power head 12, and a lower bent
portion 26 which is bent through an arc suEficient to dispose
,`.~ the axis oE the tool 14 at an angle to the upper portion 24
of the shaEt assembly such as to dispose -the cutter tool 14
s 30 for rotation in a subs-tantially horizontal plane when the
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implement is in a convenient carrying position when the
operator is in an upright standing or walking position.
Power is transmitted from thP power head 12 to the tool 14
through the shaft assembly 10 by a drive shaft which must
be flexible in view of the necessary bent portion 26 of the
shaft assembly. Such a flexible shaft 28 requires close
- support in a sheath or caslng throughout its length, and
especîally over the bent portion of the shaft assembly.
In accordance with the present invention, the
drive shaft assembly 10 is made in a series of steps or
stages shown in Figs. 2-4. The assembly starts with a
straight length of sheath tube 30. This is a rigid tube of
strong material such as steel, which is suitably cut to
`~ length. Over the length of the tube 30 which is eventually
to be bent, there is placed an elongated thick-walled cylin-
drical bushing 32 of semirigid material. This is desirably
an extruded seamless tube of semirigid plastic material of
sufficient stiffness to support the sheath tube 30 during
the bending operation described below but of sufficient
flexibility to permit such bending operation. The bushing
32 is desirably somewha-t longer than the length 26 over
which the bending will occur, so that it extends at least
partway into the ad~oining straight sections oE the final
assembly. The lower end of the bushing 32 may extend close
to the lower end of the sheath tube 30, and such sheath tube
30 desirably carries a rigid spacer bushing 34 at that lower
end. The spacer bushing is a rigid bushing of metal or the
like, and may be made as a molded bushing of powdered iron
or other metal. The lower end o~ the sheath tube 30 is
~, 30 flared outward, so that the spacer bushing 34 is trapped
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between the flare 36 and -~he thick-walled bushing 32.
The opposite end of the sheath tuhe 30 likewise
carries a rigid spacer bushing 34, and the end of the tube
is flared outward to retain that.bushing in place. Adjacent
the opposite end of the portion 24 of the shea-th tube 30
which is to be straigh~ in the final assembly, there is
another spacer bushing 38 of the same rigid metal construc-
tion as the spacer bushings 34. There may be additional
spacer bushings 38 along the straight length of the sheath
tube 30, as considered necessary or desirable depending upon
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the length and rigidity of tha~ straight section of the
sheath tube. In this first stage of assembly as shown in
.~ Fig. 2, the end spacer bushings 34 will be held against
removal from the sheath tube 30 by the flares 36. For assem-
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bly purposes, the several bushings 32, 34, and 38 may be
:. held in place by pieces of adhesive tape 40 applied to the
sheath tube 30 against the faces of the bushings.
. As a second step in the manufacture of the shaft
assembly 10, the subassembly shown in Fig. 2 is inserted in
an outer tubular frame shaft 42, which will be somewhat
~ longer than the sheath tube 30 so as to provide for attach-
'i`` ment to the power head and tool at its opposi-te ends. The
.~. frame shaft 42 is desirably of lightweight metal, such as
alwminum, and is of a size suitable to provide the necessary
~'.............. physical strength and other characteristics necessary or
~`, desired for its purposes as the main shaft of the implement
shown in Fig~ 1. The several bushings 32, 34, and 38 will
of course be of a size to fit snugly within the frame shaft
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.` 42, so that they will hold the sheath tube 30 coaxial with
' 30 that frame shaft 42 in the subassembly shown in Fig. 3~
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The second staye ac.sembly shown in Fig. 3 is then
bent to the desired configuration for the implement in which
it is to be used. Such bending is performed on conventional
tube-bending equipment which applies bending forces to the
outer frame tube 42 over the length of its bent portion 26.
These forces bend the outer frame tube 42 and are transmitted
from that outer tube 42 by ~he thick-walled semirigid bush-
ing 32 to the ~haath tube 30, so that that sheath tube 30 is
bent simultaneously with and on substantially the same
radius as the outer tube 42.
After the assembly has been bent to the condition
shown in Fiy. 4, a spacer bushing intermediate the length of
the assembly, here shown as the bushiny 38, is fixed in
place by mounting a gr~ase fitting into that bushing through
the wall of the outer frame tube 42, as shown in Fig. 6.
A hole 46 is first drilled through the frame tube 42 at a
predetermined position so that it extends through the bush-
ing 38 and into the sheath tube 30. The outer end of -the
hole 46 is threaded, and a grease fitting 44 is threaded
into that hole, so that it is engaged with the threads in
the spacer bushiny 38~ As shown in Fig. 7, to permanently
fix the upper end spacer bushing 34 in place, a local area
o~ the frame shaft 42 is deformed inward to form a dimple
~9 irNmediately adjacent the side of that spacer bushing 34.
The bushiny will then be held between that dimple 4~ and ;.
the :Elare 36 at the upper end of the sheath tube 30. At
the lowex end of the sheath tube 30, the lower spacer bush-
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iny 34 is trapped between the end flare 36 and the end of
the thick-walled bushiny 32 which now extends about the
curved portion 26 of the assembly and is thereby tiyhtly
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held against movement. '
For use of the shaft assembly 10 as shown in Fig.
4, a flexible drive shaft 28 is inserted in the sheath tube
30. The shaft and tube will have a close running fit, in
accordance with conventional practice in connection with
flexible drive shafts. The upper end of the drive sha~t 28
is provided with a suitable end fitting 48 for attachment to
the drive shaft of the power unit 12, as shown in Fig. 7.
The lower end of the shaft assembly 10 is connected
to a tool as shown in Fig. 8. An output fitting 50 is ,,
mounted by means of a tubular shank 52 in ~he open lower
end of the tubular frame shaft 42, and may be replaceably
held by a thumb screw 54. In the tool mounting shown, the
outlet fitting 50 forms a housing for,two coaxial spaced
ball bearings 56 and 58. These are spaced apart by a ring
spacer 60 interposed between their outer races, and they
are held in the housing by a snap ring 62 engaged in a
peripheral groove. A shaft 64 is mounted in the bearings
56 and 58. Such shaft carries a peripheral flange 66
trapped between the inner races of the ball bearings 56 and
58 and is thereby held axially in the fitting. The upper
end of the shaft 64 contains a squared hole which receives
a squared end member 68 on the flexible drive shaft 28. The
lower end of the shaft 64 carries a cup washer 70 and has a
threaded end on which the cutter tool 14 is mounted. The
cutter tool 1~ has one or more cutting elements 72 project-
in~ from its periphery. Such elements 72 may be made of
monofilament plastic strand which at high speed rotation
will serve as a cutting element to trim lawn and weeds~
~' 30 The shaft assembly produced as described above
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comprises an outer frame shaft 42 which pro~ides the strength
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' and other characteristics necessary and desired for if S
purposes as a frame shaft in an implement of the type
described. A rigid sheath tube 30 will be contained within
;
that frame shaft and held concentric therewith by the rigid
spacer bushings 34 and 38 at its ends and over its straight
portion 24. Over the curved portion 26 of the frame shaft
~ 42, the sheath tube 30 will be held substantially concentric
.~ with the frame tube by the semirigid bushing 32, and will
be smoothly curved along the curve of the frame tube.
Accordingly, the sheath tube 30 will provide firm guidance
and control of the rotating flexible shaft 28 throughout
substantially its entire length, so as to confine that shat
to rotation on its axis and prevent vibration and whipping
and resulting wear. The assembly provides substantially
longer life and less chance of failure than did the prior
~ art assembly containing a flexible, helically-wound sheath.
; An alternative form of semirigid thick-walled
bushing i9 shown in Fig. 9. Whereas the bushing 32 shown
'~ 20 in Fig. 5 is a circumferentially continuous, thick-walled
i~ tube, the bushing 132 shown in Fig. 9 is similar except that
it includes an axial slit 134 along its length. Such a
slit 134 may facilitate manufacture of the thick-walled tube
`~ to uniform thickness, and may be used in place of the cir-
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`~ cumferentially-continuous bushing 32 and in substantially
the same manner.
In the modification of Fiys. 10 and 11, a straight
lenyth of sheath tube 222 is first assembled with a lower
end spacer 224, an upper end spacer 226, and a length of
thick-walled plastic tubing 228 sufficient to form a
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continuous spacer extenaing from the lower spacer 224
upward through the bent portion of the frame tube 142 and
over a considerable length of the straight portion thereof
to provide support for the straight portion of the sheath
tube 222. The spacers may be held temporarily in place with
wrappings of tape 221. The ends of the sheath tube 222 are
then flared to form retaining flanges 223 at the outer faces
of the end spacers 224 and 226. This assembly is then
inserted in a straight length of rame tube 142, and the
resulting assembly is then bent to the configuration shown
in the drawings.
For purposes of mounting the arbor shaft 220 in
' the lower end of the frame tube 142, such lower end is
expanded to form a sleeve 229 to a size sufficient to receive
an arbor assembly. The arbor assembly comprises the arbor
shaft 220 which has an enlarged upper end defining a shoulder.
;.
Two ball bearings 230 and 232 are mounted on the shaft, with
the inner race of the bearing 230 abutting against the
shoulder on the shaft and with the inner races of the two
~ 20 bearings held in spaced relation by a spacer 131. An elon-
` gated hex nut 236 is threaded on the projecting end of the
~; arbor shaft 220 and against the inner race of the bearing
232 to clamp the two bearings and the spacer 230 between
itself and the shoulder on the shaft. This arbor assembly
is inserted into the expanded lower end 229 oE the frame
` tube 142, and the end edge of the tube is then rolled inward
to form a retaining flange 234 against the outer face of the
outer race of the bearing 232.
The hexagonal nut 236 on the arbor shaft forms a
non-circular drive section which fits into a mating socket
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; in the hub of the rotating cutter head 214 to provide a
driving connection between the arbor shaft 220 and that
rotary head 214. The upper end of the arbor shaft 220 is
;:: formed with a square socket 238 to receive the squared lower
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end of the flexible drive shaft 228. Such shaft is insert-
able into the sheath tube 222 from the upper end of the
frame shaft assembly, before the frame tube is inserted into
the collar of the engine 12 to its mounted position as shown
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