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: The present invention relates to a circular saw blade provided with cutting teeth of different size arranged in a plurality of circumferential groups. 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. However, it has already been proposed to provide saw blades in which the teeth are arranged in groups in the sense that repeating pattern of tooth configuration is provided around or along the blade. In US-A-4311075 a saw blade is disclosed in which the pitch spacing between teeth is geometrically related in a repeating pattern comprising three teeth or five teeth and in which the pitch between teeth increases and decreases. In GB-A-2214866 a similar arrangement is disclosed except that the gullet depth (the depth of groove between teeth) is related to the corresponding pitch: the greater the pitch, the shallower the gullet. However since it is impossible to identify where one group begins and the other ends, it is impossible to be precise about the structure shown other than that the pitch and gullet depth are (at least approximately) sinusoidal in their variation around the blade. One principal aim of a 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. 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. 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. 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. According to the present invention, a circular saw blade is provided with cutting teeth of different size arranged in a plurality of circumferential groups, characterised in that the pitch of successive teeth of each circumferential group first reduce and then increase in the direction of cut, in that the depth of gullets of successive teeth first reduce and then increase in said direction, and in that said group are separated by clearance slots at the beginning and end of each group. Preferably, the pitch and gullet depth between any two teeth are directly related to each other. 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. The gullet which precedes the tooth in the direction of cut serves to provide the space required for the operation of the tooth, including the egress of cutting debris from the cut. The greater the pitch of a tooth, then the more material that tooth will remove in its passage through the work piece. Consequently it requires a deeper gullet to assist debris removal. 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. 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: The figure shows a combination saw blade in accordance with the invention. Saw blade 1 has an overall diameter of 190.5 mm and is provided with a bore 2 30.02 mm in diameter. Twenty 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. 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°. 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. 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. 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: A circular saw blade (1) provided with cutting teeth (5,6,7,8) of different size arranged in a plurality of circumferential groups, characterised in that the pitch of successive teeth (5, 6, 7, 8) of each circumferential group first reduce and then increase in the direction of cut, in that the depth of gullets (9, 10, 11, 12) of successive teeth first reduce and then increase in said direction, and in that said groups are separated by clearance slots (13) at the beginning and end of each group. A circular saw as claimed in Claim 1, wherein the pitch and gullet depth between any two teeth are directly related. A circular saw blade as claimed in Claim 1 or 2, wherein each group comprises at least four teeth (5, 6, 7, 8) 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. A circular saw blade as claimed in Claim 3, wherein the pitch of the second tooth equals that of the fourth. A circular saw blade as claimed in any one of the preceding claims, wherein hard-material reinforcement is provided for each tooth. A circular saw blade as claimed in Claim 5, wherein said reinforcement comprises tungsten carbide tips.

Inventors: BROCKLEHURST HIRAM, MULROY MICHAEL JAMES, BROCKLEHURST, HIRAM, MULROY, MICHAEL JAMES
Applicants: BLACK & DECKER INC, BLACK & DECKER INC.
Application year: 1991
Main classification: B23D61
IPC codes: B23D61