HK1124209B - Grass-cutting head with spiral guide channels for the cutting line - Google Patents

Description

Grass-cutting head with helical guide channel for cutting line

Technical Field

The present invention relates to a grass-cutting head for cutting vegetation, and more particularly to a grass-cutting head of the line type, that is to say of the type in which the cutting member is constituted by a line projecting radially from the head and which cuts the surrounding vegetation by centrifugal force.

State of the art

For gardening work both at amateur and professional level, it is common to use grass cutting heads for cutting grass and other vegetation, which have cutting lines that project radially from the body of the head and cut the vegetation due to the centrifugal force exerted thereon and the rapid rotation of the head about its axis.

Examples of this type of grass-cutting head are illustrated in the following U.S. patent applications: US 4097991, US 4104797, US 4145809, US 4161820, US 4259782, US 4203212, US 4274201, US 4651421, US 4738085, US 4805306, US 4813140, US 4823465, US 4882843, US 4893410, US 4942664, US 4959904, US 4989321, US 5010649, US 5526572, US 5095688, US 5136782, US 5295306, US 5490641, US 5657542, US 6141879, US 6163964, US 6851191.

In conventional grass-cutting heads, the outlet holes of the cutting line can be produced directly in the body of the casing forming the line reel (as in US-A-4148141), or in A metal bush inserted in A corresponding seat produced in the peripheral wall, generally cylindrical, of the body housing the reel (US-A-4097991).

US-A-4271595 describes A line-type grass cutting head in which two cutting lines project obliquely with respect to the radial direction from the head body. To this end, the bush defining the outlet hole for the cord has a passage for the cord so that the cord passes through the passage with a straight line but with a substantially inclined trend with respect to the radial direction, instead of being parallel to the above-mentioned direction as in conventional grass cutting devices. This particular arrangement has the function of reducing wear and overheating of the wire at high rotational speeds. The bore of the bushing opens onto the cylindrical surface of the body of the head.

In all conventional heads, including those produced as described in US patent No.4271595, the cutting line is subject to frequent interruptions due to the high impact on any possible obstacles (such as stones, clods of earth or the like) around the head and due to the presence of any particularly rough vegetation. The interruption of the wire often occurs at the level of the hole through which the wire is fed from the body forming the casing for the reel on which the cutting wire is wound. When this occurs, considerable difficulties may be encountered in passing a portion of the new wire required to continue the cutting operation through the hole. In particular, if the reel accidentally rotates even by a slight angle after the line is interrupted, the active end of the cutting line is completely retracted inside the body of the head, which must be opened in order to pass the end of the line into the bush or hole, projecting it from the body of the head through said hole by a length which is sufficiently long to allow the correct operation of the lengthening devices normally present in grass-cutting heads.

Us patent No.4114269 describes a line-type grass-cutting head in which the outlet hole of the cutting line is defined by two rectilinear edges parallel to the longitudinal axis of the head. The front edge, or the edge further forward with respect to the direction of rotation of the head, has a tear-drop shaped cross section, that is to say it is thicker than the rest of the approximately cylindrical wall of the body in which the cutting line reel is housed, the outlet hole of the cutting line being produced in said wall. This configuration has the purpose of reducing the stresses and overheating of the wire, but does not overcome the above-mentioned drawbacks related to the shrinkage of the broken end of the wire into the housing of the reel.

Objects and summary of the invention

The object of the present invention is to provide a grass-cutting head which overcomes, in whole or in part, the above-mentioned drawbacks, and in particular reduces the tendency of the line to break during cutting due to collisions with obstacles surrounding the head and/or facilitates the projection of the line even if the line breaks at the level of the outlet hole or at the level of the outlet bushing in the body of the head.

These and other objects and advantages, which will be apparent to those skilled in the art from reading the text below, are obtained essentially as described in claim 1. The dependent claims relate to further possible and advantageous features of the invention.

In substance, the invention provides a grass-cutting head having an axis of rotation and a body forming a housing for at least one spool of cutting line, provided with an outlet hole for at least one end of said cutting line wound on said spool, and comprising, for each hole, a guide channel for the cutting line, extending from the inside of said housing towards the outlet hole and having an inclined development, gradually moving away from said axis of rotation. According to an advantageous embodiment, the outlet opening is inclined on the surface at an angle different from 90 ° with respect to the radial plane. The radial plane contains the axis of rotation and passes through the center of the hole. In essence, in a preferred embodiment, the or each outlet aperture is located on a surface which intersects a substantially cylindrical wall of the body of the head.

In practice, the passage is produced in portions of the body of the head which gradually project with respect to a basic shape of said body, which has substantially a circular section, the thread being fed from said projections in a non-radial orientation, but inclined with respect to a radial plane. In this way, an improved operation of the head is obtained as a result of possible collisions with obstacles surrounding the head during operation.

In a practical embodiment, the or each outlet hole may define a direction of projection of the line from the main body of the head inclined with respect to the radial direction by an angle of between 30 ° and 90 °, and preferably between 60 ° and 90 °.

Preferably, the guide channel of the cutting line may preferably have an approximately helical shape, which is generally considered herein to be a curve having a variable radius of curvature so as to move progressively away from an axis or centre coinciding with the axis of rotation of the head.

Preferably, the surface on which the outlet orifice is located forms an angle with the above-mentioned radial plane, said angle being between 0 ° and 80 °, preferably between 0 ° and 45 °, and even more preferably between 0 ° and 30 °.

According to a possible embodiment of the head according to the invention, associated with each outlet hole of the cutting line is a respective tangential tab projecting with respect to the body of the grass-cutting head. These projections, advantageously mounted on the projections inside which the guide channels of the wire are produced, can be interchanged and optionally can have teeth, i.e. formed on the surface facing radially towards the outside of the head.

In a possible embodiment, the body of the head has, in a top plan view, a substantially circular shape, and, integral with said body, for each of said hole or holes, is a projection of gradually increasing extension in the radial direction, inside which said guide channel extends. The profile of the projection is preferably approximately a portion of a spiral.

In a possible embodiment, the body of the grass-cutting head comprises: a cup portion defining a housing for a spool of cutting wire; an annular portion connected to said cup portion defining one or more of said guide channels with said cup portion; a removable closure.

According to an advantageous embodiment, each of said guide channels extends around the axis of rotation of said grass-cutting head by an angle equal to at least 30 °, preferably equal to or greater than 45 °, and even more preferably equal to or greater than 60 °, for example also between 80 ° and 120 °.

According to a different aspect, the invention relates to a grass-cutting head having an axis of rotation and a body forming a housing for at least one spool of cutting line, having at least one outlet hole for one end of said cutting line wound on the spool, the body having a toothed external profile, the respective outlet hole of the cutting line being located at the level of each tooth of said profile. The grass-cutting head as a whole will therefore no longer have the conventional circular shape in top plan view, but will feature a projection forming the above-mentioned tooth, at the level of which the line projects in a non-radial direction of the projection.

In practice, each tooth of the above-mentioned toothed profile has a first side inclined with respect to the radial direction by an angle not exceeding 45 °, and preferably between 0 ° and 30 °, on which the respective outlet hole of the line is produced. Furthermore, in accordance with a preferred embodiment of the present invention, each tooth has a second curved side having a preferably approximately helical development. A guide channel for the string extends inside each of the above-mentioned teeth.

Brief description of the drawings

The invention will be better understood from the following description and the accompanying drawings, which illustrate some practical non-limiting examples of embodiments of the invention. More specifically, in the drawings:

figures 1 and 2 show a bottom view and a top view, respectively, of a first embodiment of a grass-cutting head according to the invention, from which an optional cover has been removed in order to visualize the internal structure;

figures 3 and 4 show perspective views from two different angles of the head according to figures 1 and 2;

FIG. 5 shows a perspective view of a head similar to that of FIGS. 1-4, but configured for a greater number of cutting lines;

FIG. 6 shows a plan view taken along the line VI-VI in FIG. 5;

FIG. 7 shows an exploded isometric view of a head according to an improved embodiment of the present invention;

FIG. 8 shows a perspective view of the head of FIG. 7 in an assembled configuration;

figure 9 shows a cross-sectional perspective view of a diametric plane of the head according to figures 7 and 8;

FIG. 10 shows a side view of the head of FIGS. 7-9;

FIGS. 11-14 show a view in transverse plane and a cross-sectional view with traces XI-XI, XII-XII, XIII-XIII and XIV-XIV, respectively, according to FIG. 10, wherein the head is shown without the closure lid in FIG. 13;

FIG. 15 shows a perspective view of a modified embodiment of the head;

fig. 16 and 17 show a perspective view and a cross-sectional view, respectively, according to the middle of the head in another embodiment.

Detailed description of the preferred embodiments of the invention

With initial reference to figures 1 to 4, in a first embodiment, the grass-cutting head according to the invention, designated as a whole by the reference numeral 1, has a body 3, the body 3 being made up of a main part, substantially in the form of a casing, shown in figures 1 to 4, and optionally a closing cover, not shown, which defines, in a cup portion, a chamber 13 for housing a reel, schematically indicated by the reference numeral 5 (figures 2 and 4), on which reel 5 one or more cutting lines F1, F2 are wound. On the outside, the body 3 of the grass-cutting head 1 has, in top plan view, a substantially circular extension, the maximum diameter of which is defined by the diameter of the circular flange 7. Extending below the circular flange 7 are two projections, indicated with 9, said flange 7 having a basic configuration coinciding with the substantially circular section of the body 3.

These projections have an approximately helical development, in the sense that they are defined by an external curved surface 9A, said curved surface 9A moving progressively away from the body 3 of the head from a point 9B of connection with the cylindrical wall of the body 3, to a point 9C, said point 9C having a maximum radial distance from the axis of rotation a-a of the head. Moreover, each projection 9 has a flat surface (in the embodiment shown), indicated with 9D, which has an inclination of an angle β with respect to a radial plane, that is to say a plane containing the axis of rotation a-a, passing through the central zone of the surface 9D (fig. 2). The angle formed by the direction in which the cutting lines F1, F2 project with respect to the radial direction is denoted by γ. If the line projects perpendicularly to the leading surface 9D of the projection 9, the sum of the angles β and γ may be equal to 90 °, but this is not a constraint, as can be seen in the embodiment shown.

In fact, each projection 9 forms a tooth that protrudes from the body of the grass-cutting head 1, in the embodiment shown, the projections 9 have sides (9A, 9D) that are mutually different in shape and/or inclination.

In an approximately central position, the surface 9D has a hole 11, from which hole 11 a cutting line F1 or F2 projects. In the embodiment shown, the holes 11 are produced directly in the base material forming the body 3 (or the lower part of said body) and the projections 9. It is also possible for the holes 11 to be formed in a bush inserted inside the base material forming the projections 9 and/or the body 3.

As can be seen in particular in fig. 2 and 4, both a housing, indicated with 13, for the reel 5 and a pair of guide channels 15 are defined inside the body 3, said guide channels 15 being produced in the material forming the tabs 9, the tabs 9 extending more or less helically. These guide channels 15 each have an inlet, which is innermost in the radial direction at the level of the fillet 15A produced in the base material forming the body 3, and an outlet, which is at the level of the respective outlet of the cutting line F1 or F2, with the holes defining the radially outermost points of the guide channels. Alternatively, the channels may be made of a material different from the base material of the head of the body, for example by metal inserts inserted in an injection mould for plastics. The projections 9 can also be made of the same material as the body 3 or of a different material, the projections 9 optionally being moulded with the body 3 or by inserts arranged in a mould before the resin with which the body 3 can be made is injected.

Each guide channel 15 therefore extends through an angle a (figure 2) around the axis of rotation a-a of the head. The wires F1, F2 project with their free ends from the respective holes 11 in a direction which substantially forms a helical extension of the median line defining the guide channel 5. It must be understood that the spiral shape is not necessarily intended herein to be seen as a spiral in a mathematical or geometric sense, but in a more general sense as the shape of the guide channel 15, where this extends from the inlet (at the level of the edge 15A) to the outlet formed by the hole 11, while extending gradually away from the axis a-a towards the radial direction outwards. If necessary, the guide passage 15 may have a straight line configuration or a configuration formed by a straight line portion gradually changing in angle from the inlet to the outlet.

With this arrangement, two substantial covered effects are obtained. On the one hand, when the head is rotated (the direction of rotation being indicated by F1 in fig. 1), the side surfaces, that is to say the sides 9A of each of the two projections 9, tend to move any obstacles, such as stones, pieces of hardened soil, in particular rough plants or the like, away from the hole 11, so that these obstacles do not hit the line F1 or F2 at a point too close to the line F1 or F2 projecting from the grass-cutting head 1. This means that any interruption of the wire caused by a violent impact against an obstacle occurs at a distance from the outlet hole 11, thus avoiding the risk of the free end of the severed wire remaining inside the body 3 of the head 1.

Secondly, even if the interruption of the line occurs at the level of the hole 11 (at the level of the hole), it is possible to subsequently project a new portion of the line F1, F2 in order to restore the cutting function of the grass-cutting head 1, since a large part of the last turn of the cutting line F1, F2 inside the grass-cutting head 1 is guided inside the guide channel 15. Thus, contrary to the case of conventional grass-cutting heads, even if the line is interrupted close to the wall of the head and therefore close to the hole 11, the cutting length of the above-mentioned cutting line cannot be restored.

The angular extension a of the guide channel 15 need not be as wide as shown in fig. 1-4 (here approximately equal to or slightly greater than 90 °). Conversely, this angle may also be equal to or less than 60 °, although a wider angle is particularly useful for ensuring the second function described above.

Figures 5 and 6 show a slightly modified embodiment of the head described above in perspective view and in bottom plan view, respectively, taken according to the line VI-VI in figure 5. The same reference numerals denote the same or equivalent components as those in the above-described embodiments. In this case, the body 3 of the head, or more precisely the lower part of the same body, has 4 projections 9 instead of 2, so that 4 cutting lines (not shown) can project from the corresponding holes 11 of the grass-cutting head 1. In this case the angle alpha along which the 4 guide channels 15 extend will be slightly less than 90 deg..

Fig. 7-14 show a modified embodiment of the head according to the invention. The head is indicated as a whole by 101 and has a body 103, the body 103 being formed by a cup portion 103A, an annular portion 103B and a cover 103C, the annular portion 103B being permanently attached to the cup portion 103A (i.e. even by gluing, welding or the like, or by screws, rivets, pins or by other means), and the cover 103C being removable so as to allow access to the inside of the chamber housing the spool of cutting line. The chamber is defined by portions 103A and 103B of the body 103. In this embodiment, the reel, indicated with reference 105, is produced as shown in US-A-6851191, the content of which is expressly regarded here as an integral part of the present description and to which reference may be made for further constructional details.

Internally, this reel 105 is an elastically stressed slider 106, said slider 106 cooperating with two sets of teeth produced on the inside of the hub of the reel 105 so as to be able to lengthen the wire wound on said reel. The slider 106 slides in an axial direction on a pin 108, said pin 108 being torsionally connected to the cup portion 103A of the body 103 of the head. There is also a torsional connection between the slide 106 and the pin 108, consisting of a set of grooves 108A (fig. 7) on the pin 108 and corresponding teeth on the slide 106. The movement according to the double arrow f106 of the slider 106 is obtained by means of a push button 110, said push button 110 protruding through a hole 103D produced in the central portion of the cover 103C. When the head is mounted on A bush cutter or other working device, the button 100 projects downwards from the head so that the user can press the rotating head against the ground, thus producing A repetitive action of sliding alternately on the slider 106, and therefore A step-wise extension of the cutting line wound on the reel 105, as described above in full in US-A-6851191.

The cap 103C has an elastic protrusion 103E with which the cap 103C is connected in a notch 103F, the notch 103F being produced in the annular portion 103B of the body 103 of the head. The elastic tabs 103E are accessible from the outside (fig. 8) so that, by pressure exerted thereon, the cover 103C can be disengaged from the body 103 formed by the portions 103A, 103B of the head 101.

Once the portions 103A and 103B of the body 103 of the grass-cutting head 101 are joined together, they define a body having a basic extension with a substantially circular cross section from which a projection 109, produced partly on the cup portion 103A of the body 103 and partly on the annular portion 103B, projects in a radial direction. The projections 109 have an approximately helical conformation in the sense that their surface or side wall 109A has an approximately helical trend (in plan view) while moving progressively away from the axis of rotation a-a of the head, starting from a point 109B connected to the substantially cylindrical surface of the central body 103, until reaching a zone 109C of maximum radial dimension. Each tab 109 also has an approximately radial surface 109D, onto which radial surface 109D the respective outlet hole 111 of the cutting line opens. The direction of projection of the cutting line is therefore in this case substantially tangential, that is to say substantially perpendicular to a plane passing through the axis of rotation a-a of the head.

The projections 109 are produced partly in the material forming the portion 103A and partly in the portion 103B forming the body 103 as described above (see fig. 7). The connection of these two parts forms a channel 115 through which a corresponding cutting line (not shown) is guided. Basically, each of the two channels 115 extends from a rounded corner 115A with a substantially helical extension to the front surface 109D of the respective projection 109.

In the embodiment shown, the respective tangential tabs, which are associated with and made integral with each of the two projections 109, are interchangeable in this particular embodiment. To this end, each tab 121 has a system for connection with the body 103 of the grass-cutting head 101, i.e. reversible engagement with the body 103 of the grass-cutting head 101. To obtain this reversible engagement, in the embodiment shown, each tab 121 has a first hooked end 121A, said first hooked end 121A being inserted in a corresponding groove 131 produced in the projection 109. The opposite end 121B of each tab 121 has a through hole 121C (i.e. shaped like a small eye) and is set at the level of the outlet hole 111 of the cutting line. As can be seen in particular in fig. 9, in this embodiment the interchangeable tab 121 actually forms one side of the hole 111. As a result of how the tab 121 is positioned, its end 121B defines a bearing surface for the cutting line.

Each tangential tab 121 is connected to the corresponding protrusion 109 by first inserting the hooked end 121A into the corresponding groove 131 and then inserting the entire interchangeable tab into the seat defined between the two connection portions 103A, 103B. A pin, screw or the like is inserted into the hole 133 of the projection 109, said hole 133 being aligned with the through hole 121C of the respective tab 121. Thus, the tangential tabs 121 are permanently fixed to the head before the screws, pins or the like inserted in the holes 133 are subsequently removed, so as to be able to replace the tabs, for example due to wear.

As can be seen in particular in fig. 7 and 8, once the portions 103A, 103B and the tabs 121 are assembled, the guide channel 115 is in fact defined partly by walls formed by the material constituting the body 103 of the grass-cutting head 101, more precisely the portions 103A, 103B of the body, and partly by the radially inward facing surface 121E (fig. 7) of the respective tangential tab 121.

Instead of the cover 103C, it is also possible to omit the tabs 121 and to manufacture the body 103 of the head 101 with only two portions 103A, 103B connected to each other. The outlet holes 111 of the cutting line may also be defined in bushings, which may be made of metal, inserted in the material forming the respective projections 109. However, the use of interchangeable tangential tabs 121 is particularly advantageous because it enables worn tabs to be replaced with new ones while maintaining the integrity of the body 103 of the head. The tabs, made of a material stronger than the material forming the body 103 of the grass-cutting head 101, even if they are not interchangeable, enable the useful life of the head to be extended, since their durability is increased. For example, the tabs may be made of metal while the remainder of the head is made of molded synthetic resin. This means that the increase in cost is slight compared to a head made entirely of synthetic resin, since the projections have a limited mass. Alternatively, the protrusion may be made of the same material as the body 103. In this case they form a deposit of material which, although becoming worn, protects the rest of the head from premature wear.

Furthermore, it is also possible to use interchangeable tangential tabs 121 of different shapes, according to the type of vegetation to be cut. For example, when cutting particularly rough grass, it is possible to use tangential tabs 121 having teeth on the radially outward facing surface, said teeth effecting the cutting of the rougher vegetation.

In any case, the tangential tabs 121 also provide a protection against interruption of the cutting line caused by the latter hitting obstacles that may be found around the head during use.

Fig. 15 shows a perspective view of the head of fig. 7-14, modified in terms of the shape of the tabs, here indicated with the reference 121X. Like reference numerals designate identical or equivalent parts to those in fig. 7-14. In this case, the protrusion 121X is formed with an outer tooth 121D. Such teeth have the function of cutting or weakening vegetation or other obstacles, such as pieces of earth above the ground, which may be found around the head during use of the head, and therefore perform a mechanical action prior to the cutting action of the cutting lines F1, F2.

Figures 16 and 17 show different configurations of the head in which the outlet holes of the cutting line are radial rather than inclined towards the tangential direction. As can be seen in fig. 17, fig. 17 is a section along the plane of the parts 3A and 3B of the body 3 of a separating head, into which is housed the reel 5 on which the cutting line is wound, said cutting line projecting through a radial hole produced in a bush 201 inserted in the body of the head 1. Between the reel 5 and the respective outlet hole of each bush 201, a respective channel 15 is created, said channel 15 being substantially helical in shape and defined by two surfaces 15B, 15C, the inlet of which is defined by a fillet 15A. The shape of the channels 15 is substantially identical to that of the channels shown in figures 1 and 2, except that their ends at the level of the bushing have radial outlets 201.

It is understood that the drawing only shows an embodiment provided as a practical example of the finding, which may vary in shape and structure without however departing from the scope of the concept on which the finding is based.

Claims (34)

1. Grass-cutting head having an axis of rotation and a body forming a housing for at least one spool of cutting line, provided with at least one outlet hole of the end of said cutting line wound on said spool, and comprising, for said outlet hole or for each of said outlet holes, a guide channel for the cutting line, which extends from the inside of said housing towards the outlet hole and has an inclined shape, gradually moving away from said axis of rotation, characterized in that said guide channel has an approximately spiral shape.

2. Grass-cutting head as claimed in claim 1, characterized in that said outlet hole is present on a surface inclined at an angle different from 90 ° with respect to a radial plane containing the axis of rotation and passing through the centre of said hole.

3. Grass-cutting head as claimed in claim 1, characterized in that said one or more guide channels and said one or more outlet holes are produced in portions of the body of the head opposite to the substantially cylindrical surface of the body of the head, the or each hole being located on a surface intersecting the substantially cylindrical surface.

4. Grass-cutting head as claimed in claim 2, characterized in that said one or more guide channels and said one or more outlet holes are produced in portions of the body of the head opposite to the substantially cylindrical surface of the body of the head, the or each hole being located on a surface intersecting the substantially cylindrical surface.

5. Grass-cutting head as claimed in claim 1, characterized in that the or each outlet hole defines a direction in which the cutting line projects from the body of the head, said direction being other than a radial direction and being inclined with respect to the radial direction by an angle of between 30 ° and 90 °.

6. Grass-cutting head as claimed in claim 1, characterized in that the or each outlet hole defines a direction in which the cutting line projects from the body of the head, said direction being other than a radial direction and being inclined with respect to the radial direction by an angle of between 60 ° and 90 °.

7. Grass-cutting head as claimed in claim 2, 3 or 4, characterized in that the or each outlet hole defines a direction in which the cutting line projects from the body of the head, said direction being other than a radial direction and being inclined with respect to the radial direction by an angle of between 30 ° and 90 °.

8. Grass-cutting head as claimed in claim 2, 3 or 4, characterized in that the or each outlet hole defines a direction in which the cutting line projects from the body of the head, said direction being other than a radial direction and being inclined with respect to the radial direction by an angle of between 60 ° and 90 °.

9. Grass-cutting head as claimed in one of the claims 1-6, characterized in that the surface on which the outlet hole is situated forms an angle with the radial plane, which is between 0 ° and 80 °.

10. Grass-cutting head as claimed in one of the claims 1-6, characterized in that the surface on which the outlet hole is situated forms an angle with the radial plane, which angle is between 0 ° and 45 °.

11. Grass-cutting head as claimed in one of the claims 1-6, characterized in that the surface on which the outlet hole is situated forms an angle with the radial plane, which is between 0 ° and 30 °.

12. Grass-cutting head as claimed in claim 1, characterized in that the surface on which the outlet hole is located has a substantially radial extension with respect to the axis of rotation of said head.

13. Grass-cutting head as claimed in one of claims 1 to 6, characterized in that associated with each of said outlet holes of the line or with said one outlet hole is a respective tangential tab projecting with respect to said body.

14. Grass-cutting head as claimed in claim 13, characterized in that said tangential tabs are interchangeable.

15. Grass-cutting head as claimed in claim 13, characterized in that said projections are toothed.

16. Grass-cutting head as claimed in any one of claims 1-6, characterized in that, in top plan view, said body has a substantially circular extension, while integral with said body, for said hole or for each of said holes, is a projection having a radially increasing extension, said guide channel extending inside said projection.

17. Grass-cutting head as claimed in claim 16, characterized in that the profile of said projection or of each of said projections is approximately a portion of a spiral.

18. Grass-cutting head as claimed in claim 16, characterized in that said projections are made integral with said body from the same material as that forming said body or from a different material.

19. Grass-cutting head as claimed in claim 17, characterized in that said projections are made integral with said body from the same material as that forming said body or from a different material.

20. Grass-cutting head as claimed in claim 16, characterized in that integral with said projection or projections is a respective tangential tab which extends radially outside the profile of the respective projection.

21. Grass-cutting head as claimed in claim 20, characterized in that said tangential tabs are interchangeable.

22. Grass-cutting head as claimed in claim 20, characterized in that said tangential tabs are toothed.

23. Grass-cutting head as claimed in claim 20, characterized in that each of said tangential protrusions at least partially defines a respective guide channel.

24. Grass-cutting head as claimed in claim 20, characterized in that said projections can be reversibly engaged by hooked ends into the seats of the corresponding projections and can be locked to said projections by means of screw members or pins, near the outlet holes of the lines.

25. Grass-cutting head as claimed in any one of claims 1 to 6, characterized in that it comprises at least two holes and respective guides for the cutting line.

26. Grass-cutting head as claimed in one of claims 1 to 6, characterized in that said body comprises: a cup portion defining a housing for the spool; an annular portion connected to said cup portion defining said one or more guide channels therewith; a removable closure.

27. Grass-cutting head as claimed in claim 26, characterized in that said cup portion and said annular portion have respective projections of approximately helical shape, said one or more guide channels being defined inside said projections.

28. Grass-cutting head as claimed in claim 26, characterized in that said closure member has a substantially circular wall with an elastic projection which is releasably engaged with an annular portion of the body of said head.

29. Grass-cutting head as claimed in claim 26, characterized in that the closure member has a central hole through which the button projects in order to unwind the control line from the reel.

30. Grass-cutting head as claimed in one of claims 1 to 6, characterized in that said guide channel or each of said guide channels has an extension along an angle equal to at least 30 ° about the axis of rotation of said head.

31. Grass-cutting head as claimed in one of claims 1 to 6, characterized in that said guide channel or each of said guide channels has an extension along an angle equal to or greater than 45 ° about the axis of rotation of said head.

32. Grass-cutting head as claimed in one of claims 1 to 6, characterized in that said guide channel or each of said guide channels has an extension along an angle equal to or greater than 60 ° about the axis of rotation of said head.

33. Grass-cutting head as claimed in claim 30, characterized in that said guide channel or each of said guide channels has an extension along an angle, around the axis of rotation of said head, equal to or greater than 80 °.

34. Grass-cutting head as claimed in claim 30, characterized in that said guide channel or each of said guide channels has an extension along an angle around the axis of rotation of said head, said angle being comprised between 80 ° and 120 °.