Variable tooth saw blades

Abstract

 A variable-tooth circular saw blade (1) with cutting teeth (3) in a plurality of circumferential groups has the successive teeth (5-8) in each group first reducing and then increasing in pitch. This gives the blade an improved combination of cut, reduction of noise and vibration, together with higher speed.

Description

[0001] The present invention relates to saw blades, particularly to circular saw blades, having variable tooth size and arrangement.

[0002] Originally the teeth of circular saw blades were uniformly spaced around the circumference, and usually each tooth was of the same size. For some purposes, however, teeth of more than one size would be used, the teeth of each particular size being uniformly spaced around the circumference of the blade.

[0003] US Patent 105261 (Shailer) discloses a circular saw having alternate long and short teeth characterised in that the shorter teeth are bent further out than the longer. Even in 1870, the date of this patent, claim was only made to this specific arrangement and by disclaimer it was indicated that the variable-tooth saw was already well-known. Over the years there have been many proposals (some adopted) for vari-toothed saw blades, ranging from patterns of alternating teeth to extremely complex arrangements of groups of teeth, where great merit has been claimed for circular saws with even numbers of tooth groups (or alternatively for odd numbers of groups!) as well as for all possible variations of numbers of teeth in a group. Thus the alternating teeth of US 105261 (Shailer) can be compared with the alternating groups of teeth of US 352867 (Greist).

[0004] A summary of typical references to this variety of proposals for saw tooth arrangements can be found in US patent specification 4270429 (Brown).

[0005] One principal aim of vari-toothed saw arrangement is to optimise the compromise between cutting effectiveness and energy efficiency, and this is one object of the present invention. The so-called combination saw for woodwork is an attempt to combine the performance of rip-saw and cross-cut-saw in a single tool.

[0006] It is a further object of the invention to provide a circular saw blade having an improved combination of cleanness of cut, of reduction of noise and vibration, together with higher speed.

[0007] US patent specification 4311075 (Sundstrom) discloses a saw blade wherein the spacing of teeth in each group of a series is geometrically related, preferable so that the spacing in each group increases progressively.

[0008] More complex is the disclosure of GB patent specification 2214866 (Disston Company) which discloses circular saw blades having a plurality of groups of teeth, the teeth in each group being different from each other in both pitch (spacing) and depth. The preferred arrangement is of decreasing pitch and depth.

[0009] According to the present invention, a circular saw blade with cutting teeth provided in a plurality of circumferential groups is characterised in that the pitch of successive teeth first reduces and then increases in each group. Preferably each group comprises at least four teeth so that the pitch of the second tooth is less than that of the first, the pitch of the third tooth is less than that of the second, and the pitch of the fourth tooth is greater than that of the third. The pitch of the second tooth may be equal to that of the fourth.

[0010] Each tooth is associated with a gullet which precedes the tooth in the direction of cut and serves to provide the space required for the operation of the tooth, including the egress of cutting debris from the cut. There is a direct relationship between the pitch of a tooth and its preceding gullet so that in a saw blade according to the present invention, the depth of the gullet first reduces and then increases in each group in accordance with the reduction and the increase of the pitch of the successive teeth in the group. Just as the gullet associated with each tooth precedes that tooth in the direction of cut, so the pitch of each tooth is measured by its separation from the preceding tooth in the direction of cut.

[0011] The performance of saw blades in accordance with the present invention is enhanced by the provision of hard-material reinforcement to each tooth, preferably by the use of tungsten carbide tips.

[0012] In order that the present invention be better understood, a preferred embodiment will now be described in greater detail, by way of example with reference to the accompanying drawing in which:

[0013] The figure shows a combination saw blade in accordance with the invention.

[0014] Saw blade 1 has an overall diameter of 190.5 mm and is provided with a bore 2 30.02 mm in diameter. 20 teeth 3 are spaced round blade 1 in five identical groups, each of four teeth. A tungsten carbide tip 4 is brazed to each tooth 3. In each group, the second tooth 6 is 21° from first tooth 5, the third tooth 7 is 18° from second tooth 6, the fourth tooth 8 is 15° from third tooth 7 and the first tooth 5 of the succeeding group 18° from fourth tooth 8.

[0015] The gullet depth of each tooth is directly related to the pitch of the respective tooth so that the bottom of gullet 9 is at a radius of 78.0 mm from the centre, the bottom of gullet 10 at a radius of 80.5 mm, the bottom of gullet 11 at a radius of 83.0 mm and the bottom of gullet 12 at a radius of 80.5 mm. Each group of teeth is separated by a clearance slot 13 2 mm wide and extending to a radius of 70.4 mm. All the teeth 3 are on the same radius, have a rake angle of 20° and a clearance angle of 10°.

[0016] The illustrated embodiment of the present invention is devised as a combination cross-cut/rip saw for wood but such a saw can be effectively used on non-ferrous metals such as extrusions and castings of aluminium or copper or alloys of these and similar metals.

[0017] The variation of pitch between teeth in each group gives corresponding variation of chip size (amount of material taken by the relevant tooth) and thus to the extent of swarf removal and cleanness of the cut.

[0018] This variation eases the load on the saw blade and reduces noise and vibration and leads to a lower power requirement. This provides a greater flexibility of feed rate, readily accommodating different materials. A cleaner cut than is found with conventional combination saws is obtained which leads to an improved finish. Operational speeds up to 15% higher than with conventional combination saws can readily be achieved using the saw of the invention. The present invention is especially suitable for saws of 180-400 mm diameter.

Claims

1. A circular saw blade with cutting teeth provided in a series of circumferential groups, characterised in that the pitch of successive teeth first reduces and then increases in each group.

2. A circular saw blade according to claim 1, wherein each group comprises at least four teeth so that the pitch of the second tooth is less than that of the first, the pitch of the third tooth is less than that of the second, and the pitch of the fourth tooth is greater than that of the third.

3. A circular saw blade according to claim 2, wherein the pitch of the second tooth equals that of the fourth.

4. A circular saw blade according to any one of the preceding claims wherein hard-material reinforcement is provided for each tooth, preferably in the form of tungsten carbide tips.

Drawing