Cutting head for nylon-cord type mowers

A cutting head for a nylon-cord mower and the like, comprising a case housing an inner spool on which it is wound at least a length of nylon cord, elastically loaded by a helical spring, with the two ends of said nylon cord protruding through pairs of annular members mounted on said case in diametrally opposed locations. The inner spool is formed by a cylindrical body with at least two holes aligned along an axis intersecting the axis of the spool, and that can be axially aligned with the two annular members for allowing the replacement of the nylon cord without opening the cutting head.

BACKGROUND OF THE INVENTION 
The present invention generally refers to those devices known as grass 
mowers, i.e. hand-held motorized tools for cutting low vegetation like 
grass and weeds, and more particularly refers to nylon-cord grass mowers. 
These devices are provided with a long handle which carries at one end a 
so-called cutting head from which two lengths of nylon cord protrude for 
cutting the grass when the head is rotated. The cutting head generally 
provides a cylindrical case formed by a body and a cover, and housing a 
spool on which a supply of nylon cord or line is wound. 
Cutting heads of this kind are generally employed in cutters for lawn 
mowing as well as for farming use. The nylon cord is wound on a spool or 
bobbin that is "coiled", i.e. is elastically biased to rotate backwards by 
the cord wound on the spool, and the two cord ends freely extend outside 
the head passing through two diametrally opposed annular members. The 
motor of the device causes the cutting head to rotate and the centrifugal 
force maintains the outer portions of the nylon cord radially straight and 
acting as blades. During the use, the outside extending lengths of cord 
are worn out (by breaking) and the worn out lengths are replaced by 
releasing a certain amount of the nylon cord wound on the inner spool, so 
as to maintain a predeterminded length of the protruding nylon line, 
typically of about 20 cm. The rotation of the spool for unwinding an 
amount of nylon cord can be accomplished manually, by compressing a 
central spring and rotating the two parts by a fraction of a complete 
turn, until two series of equally spaced radial projections on the facing 
surfaces of the cover and the spool engage with each other. 
Alternatively, the lower part of the cutting head, facing the ground when 
the mower is used, can be provided with a central button, the so-called 
"tapping" button. By tapping this button against a solid surface the 
central spring is temporarily compressed and the spool is free to rotate 
until the next engagement between the projections. Such a tapping button 
can therefore be used to rotate the inner spool for increasing the length 
of the two portions of nylon cord extending outside. 
A common drawback of these known devices arises when the nylon cord supply 
has to be replaced because its overall length has become too short, and 
then the spool must be "coiled", that is the nylon cord has to be wound on 
the inner spool, for being later extracted in a controlled manner from the 
head. 
There are known devices in which when the nylon cord supply is exhausted 
the operator must open the cutting head, remove the spool, anchor a new 
cord supply to members provided on the cutting head, wind at least 
partially the new cord supply on the spool, thread the cord ends into the 
annular guide members provided on the body of the cutting head, and close 
the cutting head after correctly fitting the central spring and properly 
positioning the components. Then the new nylon cord has to be completely 
wound up, against its return force, by using in a reverse manner the 
mechanism that in use will allow the extraction of the cord. 
The above operations are complex and require a long time. Additionally, 
opening and reassembling the cutting head in the field often lead to 
losing components such as the spring or the annular members, in the grass. 
In EP-A-0 525 195 there has been proposed a nylon-cord cutting head from 
which the nylon cord is extracted by a tapping action, equipped with a 
spool bored orthogonally to its rotation axis, that allows for the 
replacement of the nylon cord supply without disassembling the device. 
Such cutting head is equipped with triangular D-shaped pawls, cooperating 
with a stopper pin housed in a hole diametrically formed within the case. 
However, such an arrangement provides for a stationary hub with a 
transverse pin, so that the through hole in the spool does not extend 
diametrically. For replacing the exhausted cord supply it is necessary to 
open windows formed on the cover, and thread the nylon cord into the 
annular members with the fingers, or by using a tool. 
Moreover in spite of the fact that the cutting head is of the tapping 
action type, the cover of the device has to be manually rotated in order 
to wind up the nylon cord, with the engagement between the stopper pin and 
the triangular pawls allowing to wind up the nylon cord on the spool. 
Another drawback of the known cutting heads comes from the undesired 
friction bonding between the coils of the cord when the mower is used. 
Finally in the conventional devices there are used different components for 
machines providing for a manual extraction of the cord and those employing 
the tapping action, and such manufacturing differences increase the 
production and maintenance costs of such devices. 
SUMMARY OF THE INVENTION 
The object of the present invention is to overcome the above mentioned 
drawbacks, and more particularly to realize a cutting head for a mower or 
similar machine that allows for a nylon cord replacement without requiring 
the opening thereof. 
In accordance with a further aspect, the cutting head of the invention 
allows for winding the nylon cord on the spool by using the same tapping 
mechanism provided for extracting the nylon line. 
In accordance with another aspect the cutting head of the invention can be 
of the type requiring a manual operation for extracting the nylon cord. 
According to the invention, the above objects are accomplished by means of 
a device as claimed in claim 1. 
Additional advantageous features are claimed in the dependent claims. 
The invention will now be disclosed with reference to the attached drawings 
that show some preferred but non limiting embodiments of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS 
With reference to FIG. 1, there is shown the general construction of a 
nylon-cord cutting head, comprising a case, formed by a body 5 and a base 
2, that houses a spool 4 on which a certain amount of nylon cord 8 is 
wound. 
The spool is fitted on a support member 10 projecting from the base 2 and 
rotatable about a central shaft 1 secured to the body 5, and is 
elastically biased by a coil spring 6 located within the support member 10 
and blocked by a plug 7. The two ends 9 of the single nylon cord 8 
protrude outside of the cutting head passing through two annular guide 
member or eyelets 3A, 3B mounted on the case in diametrically opposed 
locations. 
As above mentioned, in a conventional cutting head such as the one shown in 
FIG. 1, in order to insert a new nylon cord supply and wind it on the 
spool it is necessary to disassemble the base 2, to remove the spool and 
wind the nylon cord on it, and then the ends 9 of the cord are to be 
inserted into the annular members 3A, 3B, and finally the cutting head can 
be closed. 
In FIG. 2 there is shown the construction of a preferred embodiment of a 
spool for the improved cutting head according to the invention, comprising 
an inner spool 4 mounted between the base 2 and a body 5 (not shown in 
FIG. 2). The spool 4 comprises a cylindrical portion 20 and an inner 
bushing 25 coaxial with, and perhaps integral to, cylindrical portion 20, 
and in either case secured to a button 13 for the tapping operation. the 
bushing 25 prevents the slip off of the shaft 1 when the cutting head is 
disassembled. As a general rule, in FIG. 2 and in the other Figures the 
same references of FIG. 1 have been used for parts having similar or 
corresponding functions. 
The nylon cord 8 (not shown in the Figure) is wound on the cylindrical 
portion 20 of the inner spool 4 and such cylindrical portion is provided 
with two lateral flanges 21 and 22 which besides containing the nylon 
cord, also carry a number of projecting members 28, 28A peripherically and 
radially spaced, adapted to engage the inclined surfaces of teeth 12, 12A 
(or similar components) provided on the case, preferably on both portions 
2 and 5 of the case, and properly offset in the radial direction, as will 
be better illustrated later on. Preferably the projecting members 28, 28A 
and 12, 12A are all formed as pawls having a triangular cross section, 
with an inclined face and a vertical face which is substantially parallel 
to the axis of the spool 4. 
In the embodiment illustrated in FIG. 2, the body 20 is further provided 
with at least one radially extending intermediate annular separator 24 and 
one through hole, formed by two holes 14 aligned along an axis f--f 
intersecting the spool axis x--x, with said holes passing through the body 
20 and (partially) the inner bushing 25. The separator 24 advantageously 
prevents the overlapping of the nylon coils, so as to avoid the friction 
bonding between the coils when the mower is used. 
In accordance with the most general concept of the present invention, more 
than one pair of aligned holes can be provided in the spool. Nevertheless 
when a single nylon cord is inserted into the aligned holes of a pair, the 
holes of such pair can simply be considered as the two parts of a single 
hole passing in correspondence of a point of the axis x--x of the spool. 
Preferably the axis f--f of the holes 14 is slightly inclined with respect 
to a plane perpendicular to the spool axis of rotation x--x. As shown in 
FIG. 2, the two holes 14 are located so that one of them lies above the 
separator 24, and the other below the separator. However, as a general 
rule, the holes 14 are located within that portion of body 20 defined by 
the flanges 21, 22. Since the axial distance between two aligned holes 
depends on the size of the spool, the tilting of the axis f--f of the 
holes 14 of a pair varies within a relatively wide range. Indicatively, 
for cutting heads of conventional size, the angle formed by the axis f--f 
with the axis x--x of the spool is from 50.degree. to 90.degree.. 
Holes 14 can be axially aligned with the two annular members 3A and 3B by 
rotating the body of the cutting head with respect to the spool. At a 
position marked on the spool, the holes 14 and the annular members 3A, 3B 
are substantially aligned with each other to form a channel. Under such 
condition, the user can simply thread the end of a new nylon cord supply 8 
through the cutting head and, after checking the proper length of the two 
ends 9 protruding from the cutting head, wind the spool 4 by manually 
rotating the tapping button until all the nylon cord 8 has been wound on 
the spool. 
FIG. 3 shows a cross section of an embodiment of the complete cutting head 
according to the invention, provided with the tapping feature. As shown in 
FIG. 3, the helical spring 6 is preferably located between the cover 5 and 
the spool 4, while the button 13 is located on the opposite side with 
respect to the spring, and this construction allows the tapping operation. 
FIG. 4 is a partial cross section showing with more details the engagement 
members 28 and 28A provided on the flanges 21 and 22 of the spool 4 that 
face the teeth or pawls 12 and 12A formed on the cover 5 and the base 2, 
respectively. 
Therefore, according to the invention, for "coiling" the nylon cord 8 onto 
the spool after the nylon cord has been threaded through the transverse 
channel formed by aligning the annular members 3A and 3B with the holes 14 
of the spool, the operator only rotates clockwise the button 13 (and 
therefore the spool 4), while maintaining stationary the assembly made up 
by the cover 5 and the base 2. 
This way the radial engagement members or pawls 28A and the pawls 12A 
having a triangular cross section come to contact with their inclined 
faces and during their relative displacement axially compress the spring 6 
until the two parallel faces of the pawls cause a snapping axial movement 
and the pawls reach the relative position shown in FIG. 4. 
In operation the spool 20 is blocked against the return rotation--which 
would be caused by the tension of the two rotating cord portions--by the 
engagement between the vertical faces of the pawls or projections. 
Preferably, as shown in FIG. 4, pawls 12 are provided both on the cover 5 
and on the base 2, so that when using the tapping mechanism during mowing, 
when the button 13 is kept pushed upwards, the pawls 12--angularly offset 
by a certain amount in respect of the pawls 12A--contact the pawls 28 thus 
stopping the rotation of the spool and preventing an uncontrolled 
extraction of the nylon cord. By selecting the number of the pawls and the 
offset angle between the pawls 12 and 12A, a predetermined length of nylon 
cord 8 can be released at each axial movement of the button 13. Such 
solution allows to use the same components for both the tapping and the 
manual models of the cutting head, as will be better illustrated in the 
following with reference to FIGS. 6 and 7. 
According to the embodiment shown in FIG. 5, within the body of the spool 
20, which is formed integral with or secured to the button 13, there are 
provided means 30 for engaging and retaining the ends of the cords, at 
least in respect of moderate tractive forces, and the cutting head is 
equipped with a pair (or pairs) of nylon cords. 
The engagement means 30 can comprise a metal sheet or a small pawl adapted 
to be deformed and/or moved by the incoming end of the nylon cord, and 
capable of retaining with a certain amount of force the nylon cord to 
prevent the extraction thereof. After one or two coils of cords have been 
wound on the body of the spool, the forces generated by friction and the 
coils overlapping are sufficient to prevent the radial extraction when the 
head is rotated in use. An example of such retaining means, shown in FIG. 
8, comprises a U-folded sheet member adapted to be elastically fitted onto 
the body of the spool, with an arm provided with a hole 31, and the other 
arm provided with elastic retaining tabs 32. 
Preferably the retaining member 30 is formed by a U-folded metal sheet, on 
which a hole 31 has been drilled and tabs 32 have been punched in advance, 
and the tabs are then deformed into an opened configuration. 
FIG. 9 illustrates another embodiment of the spool 34 in which a metal tube 
35, e.g. a brass tube, is inserted into the holes 14 with end portions 36 
protruding therefrom. 
The tube 35 is a guide member for making easier the threading of the nylon 
cord into the cutting head. After the end of the nylon cord has come out 
from the spool 34, the tube 35 can be removed. However, according to an 
embodiment of the invention the tube can be permanently secured to the 
spool. In such case the end portions 36 are longitudinally slotted, 
assuming a C-shape cross section so that the nylon cord can be wound on 
the spool. In FIG. 9 the same references of FIG. 2 have been used for the 
other components so that no further description is required. 
In the proposed construction, the cutting head can be refurnished by means 
of a pair (or pairs) of shorter nylon cord lines without requiring any 
modification or difficulty in the costruction thereof. This allows for a 
better use of the nylon cord 8 by reducing the wastes, and allows for the 
replacement of only one of the nylon cords of a pair. 
Of course there are possible other different embodiments of the engagement 
means. In accordance with a further embodiment, not illustrated but easy 
to be understood, a cutting head with two or more lengths of nylon cords 
is not actually provided with dedicated engagement means, but nevertheless 
the nylon cords--after one or two coils have been wound on the spool--are 
safely retained by friction. 
Advantageously, in this last mentioned embodiment the two short lengths of 
cords left when the nylon cord supply is refurnished simply fall down by 
gravity. On the other hand in the previously illustrated embodiment 
equipped with engagement means 30 the remaining lengths of cord can be 
extracted by pushing them with a moderate force. 
Particularly in the two last illustrated embodiments, the cutting head can 
use a larger number of nylon cords protruding from the head, such as four 
or six. 
In the embodiment shown with reference to FIGS. 6 and 7, the spring 6 is 
positioned between the base 2 of the case and the spool 4, thus obtaining 
a "manual" working of the device. In this case, with the motor of the 
device shut off, the operator will pull the button 13 downwards and rotate 
it counterclockwise, thus causing the releasing of a predetermined length 
of nylon cord. FIG. 7 illustrates how in this operation are involved the 
upper projections 28 and the pawls 12 provided on the cover 5. A solution 
of this kind is of advantage when the cutting head is to be used in stony 
fields where the unintentional impact against a stone could trigger the 
tapping device should the button 13 of this latter embodiment be located 
in the lower facing surface. It is further evident that the components of 
such embodiment are equal to those of the "tapping" embodiment shown in 
FIG. 3.