GB2369546A

GB2369546A - Cutting head for a string trimmer

Info

Publication number: GB2369546A
Application number: GB0029092A
Authority: GB
Inventors: Martyn Riley; Michael Wilson
Original assignee: Black and Decker Inc
Current assignee: Black and Decker Inc
Priority date: 2000-11-29
Filing date: 2000-11-29
Publication date: 2002-06-05
Anticipated expiration: 2020-11-29
Also published as: GB2369546B; GB0029092D0

Abstract

A cutting head (8, figure 1) for a string trimmer comprising a line attachment mechanism for securing the cutting line 10 to the cutting head characterised in that the line attachment mechanism comprises: an aperture 60 in which can be located an end of cutting line 10, a line catchment mechanism around which a cutting line 10 can be wrapped in order for the line catchment mechanism to hold part of the cutting line 10 along its length; and a guide mechanism 80 through which a cutting line can pass. When a cutting line 10 is secured to the cutting head by running the cutting line 10 from the aperture 60, wrapping it around the line catchment mechanism and then passing it though the guide mechanism 80, the aperture 60, the line catchment mechanism and the guide mechanism 80 are arranged to co-operate with each other in order to secure the cutting line 10 to the cutting head (8, figure 1).

Description

CUTTING HEAD FOR A STRING TRIMMER

The present invention relates to a string trimmers and in particular to a cutting head for a string trimmer and more in particular to an attachment mechanism for attaching a cutting line to the cutting head of a string trimmer.

A typical design of String Trimmer comprises an elongate shaft having at one end a rear handle and a motor housing mounted at the other end. Located within the motor housing is an electric motor which rotatably drives a cutting head mounted upon the spindle of the electric motor about a substantially vertical axis. A cutting line extends from the cutting head which, when it is rotated by the cutting head, cuts any vegetation such as grass which enters into the path swept out by the rotating cutting line. The electric motor is powered by a mains electricity supplied by a cable which connects between the electric motor and a mains supply via a trigger switch mounted on the rear handle.

The cutting line can be mounted onto the cutting head in several ways.

However, it is usually wrapped around the spool which is in turn mounted onto the cutting head. This requires a number of components including a spool which incurs costs. This also requires additional material to make the spool which is unfriendly to the environment as the spool is discarded once the cutting line has been used.

Furthermore, the mounting of the spool can be an awkward task.

Accordingly there is provided a cutting head for a string trimmer comprising a line attachment mechanism for securing the cutting line to the cutting head characterised in that the line attachment mechanism comprises: an aperture in which can be located an end of a cutting line, a line catchment mechanism around which a cutting line can be wrapped in order for the line catchment mechanism to hold part of the cutting line along its length; and a guide mechanism through which a cutting line can pass;

wherein, when a cutting line is secured to the cutting head by running the cutting line from the aperture, wrapping it around the line catchment mechanism and then passing it through the guide mechanism, the aperture, the line catchment mechanism and the guide mechanism are arranged to co-operate with each other in order to secure the cutting line to the cutting head.

A cutting head according to the present invention provides a simple design of cutting head by which strips of cutting line can easily be attached to it. As single pieces of cutting line are utilised, no material or energy is wasted in manufacturing a spool. Furthermore, there is no requirement to dispose of any spool afterwards. The manufacture of the cutting head is greatly simplified as it is produced in a one piece construction with no moving parts. The mechanism by which the line is attached is easy to use and enable different lengths of line to be attached to the cutting head.

An embodiment of the present invention will now be described with reference to the accompanying drawings of which : - Figure 1 shows a perspective view of the String Trimmer; Figure 2 shows a perspective top view of the cutting head of the String Trimmer ; Figure 3 shows a perspective view of the bottom of the cutting head; Figure 4 shows a top view of the cutting head with a cutting line attached; Figure 5 shows a bottom view of the cutting head with a line attached to the cutting head; Figure 6 shows a top view of a cutting head without a cutting line attached; Figure 7 shows a side view of a cutting head without a cutting line attached; Figure 8 shows a bottom view of a cutting head without the cutting line attached; and Figure 9 shows a vertical cross section of the cutting head when viewed in direction x-x as shown in Figure 8.

Referring to Figure 1, the String Trimmer comprises an elongate shaft (2) having a rear handle (4) mounted on one end of the elongate shaft (2). Mounted on the other end of the elongate shaft is a motor housing (6) in which is located an electric motor (not shown). A cutting head (8) is mounted on and is rotatably driven by the spindle (not shown) of the electric motor when the electric motor is activated.

A cutting line (10) extends from the cutting head (8) and which, when the cutting head is rotated at high speed by the electric motor, cuts the grass. Part of the rear of the path swept out by the cutting line (10) when it rotates is surrounded by a guard (12) which is mounted onto the motor housing (6) of the electric String Trimmer. The electric motor is powered by a cable (not shown) which runs within the elongate shaft (2) to a trigger switch (14) mounted under the rear handle (4) An electric socket (16) is mounted underneath the rear handle (4) and which can connect to a mains power supply to power the motor via the trigger switch (14).

In use an operator would support the String Trimmer via the rear handle (4) depressing the button (14) with their index finger, thus activating the electric motor and causing the cutting head (8) and cutting line (10) to rotate at high speed.

The cutting head will now be described in more detail with reference to Figures 2-9.

Figure 2 shows the top perspective view of a cutting head (8). Figure 3 shows a perspective bottom view of the cutting head (8).

The cutting head comprises a top disc (18) and a bottom disc (20) as can be best seen in Figure 2. Located on top of the upper disc (18) is a central inner collar (22) and a central outer collar (24). The central inner collar (22) forms a bore (26) which extends two thirds of the way into the cutting head (8) as best seen in Figure 9. The bore (26) has a base (28) which seals the end of the bore (26) except for a small aperture (30) which passes through the base (28) of the bore (26).

A plurality of ribs (32) are formed between the outer and inner central collars (24, 22). This results in a plurality of apertures (34) being formed between the inner and outer collars (24,22).

Extending radially outwards from the outer central collar (24) are a plurality of veins (36) which are angularly spaced by equal amounts around the outer central collar (24). The veins (36) are used to cool the electric motor mounted within the motor housing (6) of the String Trimmer.

When the cutting head (8) is mounted on the spindle of the electric motor, the spindle is located within the bore (26) by suitable means to prevent relative rotation between the cutting head (8) and the spindle. Therefore as the spindle rotates, the cutting head similarly rotates. When the cutting head is mounted on the spindle, the veins (36) face towards the underside of the motor housing (6) of the String Trimmer.

As the veins rotate, air is forced radially outwardly from the rotating cutting head (8) thus causing air to be drawn through the motor housing (6) drawn in from air vents (38) formed on the rear of the motor housing (6) and out of the motor housing through vents (not shown) formed in the base of the motor housing (6) by the rotating veins (36).

The upper disc (18) is connected to the lower disc (20) via the central collars (22,24) and a number of walls (40) which radially extend from the central collars to the edges of the upper and lower discs (18,20), the planes of the walls (40) being perpendicular to the planes of the upper and lower discs (18,20) and which form wedge shaped apertures (42) between adjacent walls (40).

The lower disc (20) is in the form of an inverted dish as best can be seen in Figure 3. The dish comprises a rim (44) which forms the side (46) of the dish and which surrounds the dish shaped cavity (48) formed by the dish. Located within the dish is the line attachment mechanism which will now be described in greater detail.

As can be best seen in Figure 3, the line attachment mechanism comprises a central hub (50) of circular cross section and which is co-axial with the cutting head (8). A first wall (52) extends from one side of the central hub (50) towards the edge of the wall (46) of the dish as best can be seen in Figure 8. Two slots (54,56) are formed in the wall of the hub (50). The first slot (54) is formed in the wall in the side of the hub (50) opposite to that from which the wall (52) extends. The second slot (56) is formed on the same side of the hub (50) from which the wall (52) extends, the slot (56) being located on one side of the wall (52) as best seen in Figure 8. The central hub (50) forms a second bore (58) of circular cross section.

Located at the end of the wall (54) away from the central hub (50) towards the edge of the dish is a line catchment mechanism. Located near the line catchment mechanism is a small aperture (60) which is formed at the end of the wall away from the hub (50) on the side of the first wall (52) opposite to that where the second slot (56) has been formed in the central hub (50). The aperture (60) is located in the corner of a junction between the first wall (52) and a second wall (62) which forms part of the line catchment mechanism and which is formed perpendicular to the first wall (52). The length of the second wall (62) is approximately equal to the diameter of the hub (50). Extending from the ends of the second wall (62) are third and fourth walls (64,66). The third and fourth walls (64,66) extend from the second wall (62) to the edge of the dish.

The height of the first and second (52 and 62) walls above the base (68) of the dish is equal to the height of the hub (50) above the base (68) of the dish. However, the height of the third (64) and fourth (66) walls is substantially less above the base (68) of the dish.

As shown in Fig. 9, extending from the top, (the top being the edge of the second wall (62) away from the base (68) of the dish), of the second wall is a rectangular tab (69) which extends in the same direction from the second wall (62) as the third and fourth walls (64,66) but the plane of which is orientated perpendicularly from the third and fourth walls (64,66).

The third and fourth walls (64, 66) extend in a direction parallel to the first wall (52). The width of the tab (69) is less than a length of the second wall (62). Attached to the underside of the tab is a hook (70) which projects downwardly towards the base (68) of the dish as best shown in Figure 9. The hook (70) forms a rectangular slot (72). A space (74) is left forward of the hook (70) and tab (69).

On the side of the wall (46) of the dish opposite to that of the line attachment mechanism is a guide mechanism in the form of a tunnel (80) which passes from the inner area of the dish through the wall (46) of the dish to produce a hole (82) on the outside of the wall (46) of the dish. The guide mechanism and aperture (60) are thus located on the same side of the line catchment mechanism. At the entrance (84) to the tunnel is formed a fifth wall (86) which is parallel to the first wall (52). A sixth wall (88) is formed opposite the fifth wall (86) and which curves away from the fifth wall (86). The inner side walls (90,92) of the tunnel curve outwardly from the entrance to the exit as best shown in Figure 5 where the walls are indicated by the dashed lines. Located on either side of the guide mechanism, are six pillars (94) which has been formed adjacent the rim of the dish. These have been formed to counteract the mass of the line attachment mechanism so that when the cutting head (8) rotates the centre of mass is located on the axis of rotation of the cutting head.

In order to attach a cutting line to the cutting head, one end of the cutting line (10) is inserted into the aperture (60) is then fed around one end of the second wall (62), over the third wall (64), through the slot (72) formed by the hook (70) where the line is retained, over the fourth wall (66) around the other end of the second wall (62), through the second slot (56) formed in the central hub (50), across the central hub (50), through the first slot (54) formed the central hub (50), between the fifth and sixth walls (86,88) through the tunnel and extends beyond the edge of the cutting head as best shown in Fig 5. The cutting line is thereby passed through an angle of greater than 1800 when it is wrapped around the line catchment mechanism.

The guide mechanism, the line catchment mechanism and the small aperture (60) co-operate with each other to secure the cutting line (10) to the cutting head.

The walls (90,92) of the tunnel (80) are curved in order to prevent damage to the cutting line (10) particularly when it impacts something hard causing it to bend backwards as it rotates. By passing the cutting line (10) through the central hub. it provides additional control of the movement of the line (10) within the dish. The cutting head is made from plastics material in a one piece construction.

Claims

1. A cutting head (8) for a string trimmer comprising a line attachment mechanism for securing the cutting line to the cutting head (8) characterised in that the line attachment mechanism comprises: an aperture (60) in which can be located an end of a cutting line, a line catchment mechanism around which a cutting line can be wrapped in order for the line catchment mechanism to hold part of the cutting line along its length; and a guide mechanism through which a cutting line can pass; wherein, when a cutting line is secured to the cutting head by running the cutting line from the aperture, wrapping it around the line catchment mechanism and then passing it through the guide mechanism, the aperture (10), the line catchment mechanism and the guide mechanism are arranged to co-operate with each other in order to secure the cutting line to the cutting head.

2. A cutting head as claimed in claim 1 wherein the aperture (60) and guide mechanism are located on the same side of the line catchment mechanism so that when a cutting line is secured to the cutting head the cutting line runs from the aperture (60), wraps around the line catchment device through substantially 1800 or greater and then towards and through the guide mechanism.

3. A cutting head as claimed in either claims 1 or 2 wherein the guide mechanism is located at the edge of the cutting head so that when a cutting line is secured to the cutting head, the cutting line would pass through the guide mechanism and extend beyond the cutting head.

4. A cutting head as claimed in any of the previous claims wherein the guide mechanism is in the form of a tunnel (80) through which a cutting line can pass.

5. A cutting head as claimed in any one of the previous claims wherein one side of the cutting head is shaped as a dish, the guide mechanism being located within the wall (46) of the dish, the aperture (60) being formed in and the line catchment mechanism being mounted on the inner base (68) of the dish.

6. A cutting head as claimed in any one of the previous claims wherein the guide mechanism comprises at least one inner side wall (90) which is curved.

7. A cutting head as claimed in claim 6 wherein the guide mechanism comprises two inner side walls (90,92) which are curved.

8. A cutting head as claimed in any one of the previous claims wherein there is provided a fifth wall (86) which extends from one side of the entrance (84) of the guide mechanism.

9. A cutting head as claimed in claim 8 wherein a side of the fifth wall (86) runs flush with one of the inner side walls of the guide mechanism.

10. A cutting head as claimed in either of claims 8 or 9 wherein the side of the first wall is straight.

11. A cutting head as claimed in any of claims 8 to 10 wherein there is a sixth wall (88).

12. A cutting head as claimed in claim 11 wherein a side of the sixth wall (88) is curved.

13. A cutting head as claimed in either of claims 11 or 12 wherein the side of the sixth wall is flush with an inner side wall (90) of the guide mechanism.

14. A cutting head as claimed in any one of the previous claims where there is provided a hub having two slots and which is arranged so that when a cutting line is

secured by the line attachment mechanism, it passes from the line catchment mechanism, through the first slot, through the hub, through the second slot and towards the guide mechanism.

15. A cutting head as claimed in any one of the previous claims wherein the line catchment mechanism comprises a hook (70).

16. A cutting head as claimed wherein the line catchment mechanism comprises a second wall (62), a tab (69) which extends from the top of the second wall, the plane of the tab (69) being perpendicular to the plane of the wall (60), the hook (70) being attached to the underside of the tab (69) which projects downward from the tab (69).

17. A cutting head as claimed in either of claims 15 or 16 wherein the hook (70) forms a slot (72).

18. A cutting head as claimed in claim 17 wherein the line catchment mechanism comprises a third and fourth walls (64,66) which have planes perpendicular to the plane of the second wall (62) and the tab (69), the height of the third and fourth wall being less than that of the second wall (62) wherein, when a cutting line is attached to the cutting head, it passes over the third wall (66) through the slot (72) and over the fourth wall (66).

19. A cutting head as claimed in any one of claims 15 to 18 wherein there is further provided a first wall (52) which extends from the hub (50) to the second wall (62) and which is perpendicular to the second wall.

20. A cutting head as claimed in claim 18 wherein the aperture (60) is formed in the comer where the first wall (52) and second wall (62) meet.

21. A cutting head as claimed in claim 19 wherein the second slot (56) of the hub (50) is formed in the hub (50) on the opposite side of the first wall (52) to that of the aperture (60).

22. A string trimmer comprising: an elongate shaft ; and a cutting head rotatably mounted on the elongate shaft characterised in that the cutting head is as claimed in any one of the claims 1 to 21.

23. A cutting head as hereinbefore described with reference to the accompanying drawings.