Technical Field

This invention relates to a saw blade and, in particular, to the arrangement of teeth on a saw blade. Background Art

Saws and saw blades come in all shapes and sizes. However, as used herein, a saw blade refers to a blade for a bow saw and circular saw blades for use with power drills and the like.

A bow saw, in this context, refers to a metal-framed crosscut saw in the shape of a bow, which can be used for cross-cutting branches or firewood, up to 150 mm in diameter. It may also be used for ripping suitable timber. This type of saw is also known as a Swede saw, a Finn saw or a bucksaw. The saw blade is a thin, narrow, metal strip with a coarse set of teeth running along one edge, and is held under tension between the ends of the bow-shaped metal frame. A worn saw blade may be easily replaced by a new blade, if required.

A bow saw will cut through dry, low density timber, such as deal, with ease. However, the saw blade can jam in green timber and can be difficult to release. Circular saw blades are available in a variety of designs, to suit a particular application. They are used in a professional setting and also by the Do It Yourself (DIY) user. In this latter setting, use of a power drill, with insufficient power for a particular application may result in jamming of the blade. Also, an underpowered drill can cause the saw to slow down causing excessive friction. This can result in over heating of the blade, which can become distorted or bum the cut surface.

The width of the kerf i.e., the slot the blade cuts in the material is an important consideration. The size of the kerf is determined in part by the thickness of the blade, and a solid, reliable blade is one of the features of a good blade. However, the thicker the blade the more power that is required and this is where the DIY user can encounter problems.

It is an object of the present invention to overcome the disadvantages of the saw blades hereinbefore described.

Disclosure of Invention

Thus, the invention provides a saw blade comprising a metal plate, a primary set of teeth located on one edge thereof, a first and a second secondary set of teeth attached on opposite sides of the plate and stepped back from the primary set of teeth, such that, in use, the primary set of teeth is first engaged with a piece of material to be sawed followed by engagement of the piece of material with both the first and the second secondary sets of teeth, once the primary set of teeth has made an initial cut in the piece of material.

An advantage of the saw blade in accordance with the invention is that, in use, once the first and second secondary sets of teeth engage with the piece of material, the width of the kerf is increased from the initial width of the kerf cut by the primary set of teeth. This increased kerf width, coupled with the fact that three sets of teeth are now cutting into the piece of material, results in a more rapid cutting time with less chance of the saw blade sticking in the piece of material.

Preferably, the first and the second secondary sets of teeth are each attached to the plate by welding means.

An advantage of welding as an attachment means for the secondary sets of teeth is that the teeth are securely attached to the metal plate.

Further, preferably, the welding means is spot welding.

An advantage of using spot welding is that the secondary sets of teeth may be fused to the metal plate, and accidental separation of the secondary teeth from the metal plate is minimised. Alternatively, the first and the second secondary sets of teeth are attached to the metal plate by a metal-to-metal adhesive.

An advantage of the use of a suitable metal-to-metal adhesive is that the width of the metal plate, with the secondary teeth attached, can be maintained within a tight tolerance along the length of the saw blade. This results in a balanced saw blade. In one embodiment of the saw blade in accordance with the invention, the plate is a standard bow saw blade.

An advantage of the use of secondary sets of teeth on a bow saw blade is that the resultant saw blade is less likely to jam when compared to an unmodified saw blade. Furthermore, by having three sets of teeth the sawing can be completed in less time than when using an unmodified saw blade.

In a further embodiment of the saw blade in accordance with the invention, plate is a circular saw blade. An advantage of adding secondary sets of teeth to a circular saw blade is that the saw blade will cut through a piece of material in less time than when using an unmodified circular saw blade and there is less tendency for the blade to slow down due to the increase kerf width.

Preferably, the first and the second secondary sets of teeth are each respectively attached to a first and second secondary metal plate, which secondary metal plates are concentric with the metal plate.

An advantage of the use of secondary metal plates is that the resultant sandwich created by the secondary plates and the metal plate therebetween results in a balanced, modified circular saw blade. Further, preferably, the metal plate and the first and second secondary metal plates are attached together by spot welding. An advantage of spot welding the secondary metal plates to the metal plate is that the resultant modified circular saw blade, is strong and so is unlikely to fail in use.

Alternatively, the metal plate and the first and second secondary metal plates are attached together by adhesive means.

An advantage of the use of adhesive means to attach the secondary plates to the metal plate is that a uniform thickness of the resultant modified blade can be assured.

Suitably, a surface of the first and second secondary metal plates has an abrasive band on the surface thereof inside the location of the first and the second, secondary set of teeth.

An advantage of the inclusion of an abrasive band on the secondary plates is that the abrasive action will tend to smoothen the edges of the cut as the saw blade passes through a material piece. The invention will be further illustrated by the following description of embodiments thereof, given by way of example only with reference to the accompanying drawings in which:

Brief Description of Drawings

Fig. 1 is a view from one side of a saw blade for a bow saw in accordance with the invention; and Fig. 2 is a view from one side of a saw blade for a circular saw in accordance with the invention.

Best Mode for Carrying out the Invention

Referring to Fig.l, there is illustrated generally at 10, a saw blade in accordance with the invention, which saw blade 10 is for use in a bow saw (not shown). The saw blade 10 comprises a metal plate 11 with a primary set of teeth 12 located on one edge 13 thereof. A first secondary set of teeth 14 is attached to one side 15 of the metal plate 11, with the first secondary set of teeth 14 being stepped back from the primary set of teeth 12.

A second secondary set of teeth (not shown) is attached to the opposite side 16 of the metal plate 11, with the second secondary set of teeth being similarly positioned on the opposite side 16 as in the case of the positioning of the first secondary set of teeth 14 on side 15 of the metal plate 11.

The first 14 and a second (not shown), secondary sets of teeth are attached to the respective sides 15, 16 of the metal plate 11 by spot welding.

In use, the primary set of teeth 12 is first engaged with a piece of material (not shown) to be sawed followed by engagement of the piece of material with both the first 14 and the second (not shown), secondary set of teeth, once the primary set of teeth 12 have made an initial cut in the piece of material. Referring to Fig. 2, there is illustrated generally at 20, a further embodiment of a saw blade 29 in accordance with the invention, which saw blade 20 is for use as a circular saw. The saw blade 20 comprises a circular metal plate 21 with a primary set of teeth 22 located on the periphery 23 thereof. A first secondary set of teeth 24 is attached to a first secondary metal plate 25, at the periphery 26 thereof, which first secondary set of teeth 24 is stepped back from the primary set of teeth 22. The metal plate 21 and the first secondary metal plate 25 are attached together by spot welding. An abrasive band 27 is located on side 29 of the first secondary metal plate 25.

In a similar fashion, a second secondary metal plate (not shown) is attached to the opposite side 30 of the metal plate 21 by spot welding. The second secondary metal plate has a second secondary set of teeth (not shown) attached at the periphery thereof, together with an abrasive band located on the second secondary metal plate at an equivalent position to band 27 on the first secondary metal plate 25.

Thus, the saw blade 20 has three sets of teeth, with the primary set of teeth 22 sandwiched between the first 24 and second secondary sets of teeth. In use, the primary set of teeth 22 is first engaged with a piece of material (not shown) to be sawed followed by engagement of the piece of material with both the first 24 and the second (not shown), secondary set of teeth, once the primary set of teeth 22 has made an initial cut in the piece of material. As the saw blade 20 cuts further into the piece of material, the abrasive bands to each side of the saw blade 20 smoothen down the edges of the cut.