Improvements in or relating to saws and saw teeth and blades therefor

Abstract: A hand-held cutting tool with a blade (8) carrying teeth (11) formed of a hard material located in slots (12) in an edge of the blade (8) is supported in a support member (2), and the blade has a support edge (41) or support edges (20,36) which run on a bearing surface or surfaces (40) or the member (2). The edge (41) is attached to a face of the blade (8) whereas the edges (20,36) are provided by the curved portions of sector shaped body portions (23 or 33) of the teeth (11) which located the teeth in the slots (12) and which are thicker than the material of the blade (8). The teeth may be located in special shaped slots (12) which include a sector-shaped part (14) and an entry part (13) having base edges (37) engaging shoulders (38) on the teeth (11), there being triangular portions (21,22 or 30,31) on the teeth (11) which overlie surface portions on the blade (8) to assist in locating and holding the teeth (11) in position in the blade.

Description: This invention relates to saws and blades therefor and has particular application to saw blades for power saws, for example circular saws, bandsaws, jig saws, sabre saws and saws with a linearly reciprocatable blade or linearly reciprocatable blades. The saws may be hand-held or bench mounted or they may be purpose built structures. The invention is also applicable to manually operated saws, for example tenon saws and bow saws. Conventionally, such saws employ steel blades formed with integral teeth which are ground and set according to particular requirements. Such blades require sharpening from time to time and are not suitable for some manufactured materials of which chip-board is an example. It has been proposed to use teeth of a hard material, for example tungsten carbide, mounted on a circular blade carrier but the mounting techniques employed do not provide a sufficient degree of security for other forms of carrier, particularly those where linear reciprocation is required. Furthermore, it is known to mount teeth in circular saw blades by use of a keyway. Different styles of keyway are disclosed in GB-A-275554, GB-A-1464640, US-A-3945289 and EP-A-0117991. Another style of keyway for a reciprocatable blade is disclosed in GB-A-665433. However, in all these known constructions, it is a difficult task to hold the teeth in position during manufacture of the blades, and it is an object of the present invention to provide a construction which simplifies manufacture. A stone sawing machine blade is described in US-A-1711016 and has hard teeth retained in shaped slots around the periphery of the circular blade. In power saws with one or more reciprocating blades, it is important to provide some form of guidance for the blade(s). When the blades have integral teeth formed in an edge region of the blade, the blade can be shaped to provide a guide surface, such as is disclosed in GB-A-2134038 or US Patent Nos.1537980 or 2840125 or DE-U-8713949. This, however, involves providing special types of blade. The present invention obviates this requirement. According to the present invention, we provide a cutting tool having a cutting blade carrying cutting teeth formed of a hard material and located in an edge of the blade in suitable slots, the cutting tool including a support member relative to which the blade moves during operation of the tool, there being a support surface or surfaces on the support member with which a support on the blade engages or engage during operation of the tool, the support surface or surfaces being parallel to the cutting edge of the blade, characterised in that the support is provided by edges of the teeth of the blade remote from their cutting edges. Preferably, each tooth has a generally sector-shaped body portion located in a sector-shaped slot in its blade, and a part of the curved edge of the sector-shaped body portion provides said support edge. Preferably, the tool has two contra-reciprocating cutting blades, each provided with a support edge or edges on its outer face. Each slot in the or each blade is preferably contoured to provide an edge or edges to support a mating edge or edges on each tooth and wherein a portion of each tooth extends at least partially into the slot, with a further portion extending beyond the slot and overlying a portion of a surface of the blade. Each slot may include an entry portion with side edges and a base edge or edges. The tip of the sector-shaped part opposite its curved part is preferably located centrally of the base edge and the sector-shaped part is also symmetrically disposed with respect to the longitudinal axis of the slot. Each part of the base edge and its adjacent side wall of the sector-shaped part define two sides of a generally triangular shaped portion, the two triangular shaped portions being the portions of the blade which are overlaid by two further portions of their respective tooth. The sector-shaped part may communicate with the entry portion via an opening in the base edge whose sides are rounded and which are tight fit with a mating portion of a tooth, the remainder of a tooth fitting into the slot with some clearance. In order that the invention can be better understood, preferred embodiments will now be described in greater detail by way of example with reference to the accompanying drawings in which:- Figure 1 is a side view of a hand-held, power saw incorporating saw blades embodying the invention, Figure 2 is a side view of a first saw blade embodying the invention, Figure 3 is a section on line III-III of Figure 2, Figure 4 is a section on line IV-IV of Figure 2, Figure 5 is a side view, on a larger scale, of a detail of the blade, Figure 6 is a side view of a second saw blade embodying the invention, Figure 7 is a plan view of a first saw tooth of a blade embodying the invention, Figures 8 and 9 are, respectively , a side and an end view of the saw tooth shown in Figure 7, Figure 10 is a scrap view of the tooth shown in Figure 5 looking in the direction of arrow X in Figure 7, Figure 11 is a plan view of a second saw tooth of a blade embodying the invention, Figures 12 and 13 are, respectively, a side and an end view of the saw tooth shown in Figure 11, Figure 14 is a scrap view of the tooth shown in Figure 11 looking in the direction of arrow Y in Figure 11, Figure 15 is a section on an enlarged scale on the line XV-XV of Figure 1, Figure 16 is a section on an enlarged scale on the line XVI-XVI of Figure 1, Figure 17 is a side view of a saw blade not being a part of the present invention, and Figure 18 is a section on the line XVIII-XVIII of Figure 17. The saw blades now to be described are for use in a hand held power saw whose construction is described in detail in European Patent Application No. 0 267 311 (86.115651.1) instead of the blade described therein. The power saw described in European Patent Application No, 0 267 311 employs two saw blades arranged in side-by-side contact and reciprocable in opposite directions by an electrically powered drive mechanism. In Figure 1, the saw blades are shown diagrammatically at 1 and are guided for reciprocating movement in a slot formed in the lower edge of a support 2 whose top-to-bottom bottom dimension (as seen in Figure 1) increases towards the housing 3 of the saw. The saw blades 1 extend into the housing where their ends are connected to a drive mechanism within the housing 3 and powered by an electric drive motor also located in housing 3. As can be seen from Figures 15 and 16, the support 2 comprises two side-by-side plates 2A, 2B whose lower (as seen in Figure 1) surfaces are spaced apart to provide a longitudinal slot 2C in which the saw blades slide. The upper parts of the plates 2A, 2B are in contact and are secured together in any suitable manner, for example, by spot welding. The housing is contoured to provide a rear closed-loop handle 4 part of which houses a control switch (not shown) that is actuable by a trigger 5. The switch controls energisation of the electric drive motor. Mounted upon the forward part of the housing 3 is a front handle 6 that extends away from the housing 3 on both sides of the latter. The saw blade 7 shown in Fig. 2 is the left-hand of the two blades when viewed in the direction of arrow Z in Fig. 1. The blade 7 comprises a length 8 of steel strip of constant top-to-bottom dimension over most of its length. The top-to-bottom dimension increases over a short length of the strip at the left-hand end thereof (as viewed in Fig. 2) and as indicated at 9. An apertured boss 10 is fixed to the strip 8 close to the left-hand end and is used to connect the blade to the drive mechanism referred to above. Adjacent to the other end of the strip 8, there is formed a short longitudinal slot 10a whose purpose is described in the application referred to above. The strip 8 is formed, in a manner described below, to receive cutting teeth 11 at spaced intervals along its length (excluding part 9). In the example shown in Fig. 2, there are twelve teeth, but only eight are shown in detail, the central axes only of the remainder being shown. The tooth pitch is not the same for all teeth, the distance between the fourth and fifth teeth from the left and between the eighth and ninth teeth from the left being slightly greater than the constant distance between the remaining teeth. The teeth 11 are of tungsten carbide and are fixed to the strip by first placing them in slots 12 cut in the strip and then brazing the teeth in position in the slots. As can be seen from Fig. 5, the slots extend into the strip from the lower (as viewed in Fig. 5) edge of the latter. The configuration of the slots is shown in Fig. 5. Each slot 12 has a parallel sided entry portion 13 which leads into a sector-shaped extension 14. The entry portion 14 has side edges and a base edge 37 which is generally parallel to the lower edge of the strip 8. The entry portion 13 and the extension 14 lie symmetrically with respect to the longitudinal axis A-A of the slot and the extension 14 joins the entry portion 13 centrally of the base edge of the latter as shown. The junctions between the base and the extension 14 are gently rounded as indicated at 15. As can be inferred from Figs. 2, 3 and 4, the slots extend for a short distance only into the top-to-bottom dimension of the strip 8. Alternate teeth along the length of strip 8 are of the configuration shown in Figs. 7-10 while the remainder are of the configuration shown in Figs. 11-14. Starting from the rift of the strip as seen in Fig. 2, odd numbered teeth are as shown in Figs. 7-10, and even numbered teeth are shown in Figs. 11-14. The tooth shown in Figs. 7-10 has a pointed portion 16, the side walls of the portion being bevelled in part as indicated at 17. In addition, the extremity of the portion is downwardly-set (as viewed in Fig. 8) as indicated at 18. The set is sufficient to ensure that the kerf cut is of a width that will permit passage of the support 2. The portion 16 merges into a body portion 19 of generally rectangular form when seen in plan as in Fig. 7 with a curved end face 20. The body portion 19 has equi-sized, triangularly-shaped areas 21, 22 over which the depth of the body portion is reduced by about one half to leave a sector-shaped platform 23 disposed centrally of the longitudinal axis B-B of the tooth and whose upper surface lies in a plane that is inclined slightly to that containing the upper surface of portion 16. This can be observed from Fig. 9 where line 24 represents the upper edge of the left-hand end (as viewed in Fig. 9) of the platform 23 and line 25 represents the edge between the upper surfaces of the platform 23 and portion 16. The areas 21, 22 are so orientated as to leave shoulders 38 which lie transversely of the axis B. As can be seen from Fig. 7, the adjacent tips of the areas 21, 22 are curved as shown at 26. The remaining teeth are of a configuration generally similar to that of the tooth shown in Figs. 7-10. Thus, as shown in Figs. 11-14, each remaining tooth has a pointed portion 27 whose edges are bevelled in part as indicated at 28. The extremity of portion 27 is not downwardly set as is the tooth shown in Figs. 7-10 but is straight as shown in Fig. 12. Those teeth ensure the removal of saw dust from the kerf. The body portion 29 of the tooth shown in Figs. 11-14 is identical with that of the tooth shown in Figs. 7-10, and has equi-sized, reduced-depth triangularly-shaped areas 30, 31 whose adjacent tips are rounded as at 32. The sector-shaped platform 33 that is disposed centrally of the longitudinal axis B-B of the tooth has an upper surface that lies in a plane inclined slightly with respect to that containing the upper surface of portion 27, the inclination being the same as that of the corresponding planes of the tooth shown in Figs. 7-10. The inclination can be observed from Fig. 13 where lines 34, 35 correspond with lines 24 and 25 of Fig. 9. The body portion 29 also has a curved end face 36, the curvature being identical with that of end face 20. The areas 30, 31 are so orientated as to leave shoulders 38 which lie transversely of the axis B-B. The teeth are sized so that the platforms 23, 33 will fit into the extensions 14 of the slots in the strip 8. The areas 21, 22 thus overlie surface parts of the plate-like strip 8 on each side of the platforms 23, 33. The surfaces of the platforms 23, 33, when the tooth is correctly positioned, lie flush with the inner surface of the strips 8 or slightly below that surface. The parallel sided entry portions 13 of the slots receive those parts of the teeth between the reduced depth areas and the pointed portions with the base 37 of each entry portion 13 supporting the shoulders 38 of the recessed areas. The platforms fit tightly in the vicinity of the rounded parts 15 of the slots but elsewhere there are some small clearances to permit the ready flow of brazing alloy during the brazing of the teeth to the strip 8. The other blade 39 is shown in Fig. 6 and is of a configuration generally similar to that of blade 7 but is its mirror image so that the blades can be placed together in side by side contact as indicated in Figs. 3 and 4 with the surfaces of the teeth platforms facing each other. The surfaces of the platforms lie flush with or just beneath the respective contacting faces of the saw blades so that side-by-side reciprocating movement of the blade is not impeded and the blades are not separated. The teeth 11 of blade 39 are located in positions corresponding with those of teeth 11 on blade 7. The teeth 11 are formed by a process in which tungsten carbide particles are first moulded into the required tooth shape and are then sintered for producing a coherent mass of particles. The tooth configuration described above faciliates the use of moulding techniques and sintering because there are no severe changes in tooth cross section. Moreover, possible distortion during sintering is minimised because the tooth form has one substantially flat or plane surface on which it can rest during sintering. Once moulded and sintered, the teeth are located in the position with the platforms engaged in the slots. The relatively tight fit between the rounded surfaces 15 and 26 ensures that the teeth are held firmly for subsequent brazing whilst limiting the area of the blade strips over which stressing occurs, because of the tight fit, to a minimum. Subsequently, the teeth are lapped to a required contour. The slot concept enables the teeth to be accurately positioned on the strip and in particular ensures that the end faces 20 and 36 of teeth on the same strip lie in line and at a constant predetermined distance from the upper (as seen in Figs. 2 and 6) edge of the strip. The end faces thus form bearing edges which slide along the upper edges of the slot in the support 2. That feature can be seen clearly in Figs. 15 and 16 which show that the curved end faces 20 and 36 of the teeth 16 and 27 respectively slide along the lower edges 40 of the plates 2A, 2B. Although not forming a part of the present invention, an alternative blade shown in Figs. 17 and 18 provides each saw blade 7, 39 with a bearing element 41 secured longitudinally to its outer face. The bearing element 41 may be a steel strip spot welded or secured in some other way to the saw blade. It may be necessary to reduce slightly the overall length of the teeth and of the slots in which they are located to accommodate the bearing element 41. When blades incorporating the bearing elements 41 are used, the elements 41 contact the lower edges 40 instead of the curved end surfaces of the teeth. Preferably, at an appropriate stage in their manufacture, the strips are chrome plated to give a hard surface finish. However, of the contacting faces of the blades, only one is chrome plated. It will be understood that the invention may be embodied in saw blades of forms different from those described above. Thus, circular saw blades may be made with teeth held in slots as may the blades of jig saws and sabre saws, although it will of course be necessary to employ different tooth profiles. It will also be appreciated that slots of different contours than those described above may be required in other applications. The contour of the slot must provide positive location of the tooth and preferably hold the latter during any subsequent processing for example brazing. In addition, support surfaces must be provided to support the tooth when exposed to loads.

Claims: A saw having a cutting blade (8) carrying cutting teeth (11) formed of hard material and located in an edge of said blade in suitable slots (12), said saw including a support member (2) relative to which said blade (8) moves during operation of the saw, there being a support surface (40) or surfaces on said support member (2) with which a support (20,36) on said blade (8) engages or engage during operation of the saw, said support surface or surfaces (2) being parallel to the cutting edge of said blade, characterised in that said support is provided by edges of said teeth (11) of the or each blade (8) remote from their cutting edge. A saw as claimed in Claim 1 characterised in that it has two contra-reciprocating cutting blades (8), each said blade having said support on its outer face. A saw according to Claim 1 or 2 characterised in that each tooth has a generally sector-shaped body portion (23 or 33) located in a sector-shaped slot (14) in said blade (8), and wherein a part of the curved edge (20 or 36) of said sector-shaped body portion (23 or 33) provides said support. A saw according to any one of claims 1 to 3, characterised in that each slot is contoured to provide an edge or edges (38) to support a mating edge or edges on the tooth it locates, and wherein a portion of the tooth extends at least partially into the slot, with a further portion (21,22 or 30,31) extending beyond said slot (12) and overlying a portion of a surface of said blade. A saw as claimed in any one of Claims 1 to 4, characterised in that each slot includes an entry portion (13) with side edges and a base edge or edges (37). A saw as claimed in Claims 3 and 5, characterised in that the tip of the sector-shaped slot (14) opposite its curved part is located centrally of said base edge (37) and said sector-shaped part is symmetrically disposed with respect to the longitudinal axis (A-A) of the slot (12). A saw as claimed in Claims 4 and 6, characterised in that each part of said base edge (37) and its adjacent side wall of said sector-shaped part (14) define two sides of a generally triangular shaped portion, said two triangular shaped portions being the portions of said blade which are overlaid by said portions (21,22 or 30,31) of their respective teeth (110). A saw as claimed in Claim 7, characterised in that said sector-shaped part (14) is in communication with said entry portion (13) via and opening in said base edge whose sides (15) are rounded and which are a tight fit with a mating portion of a tooth (11), the remainder of a tooth fitting into the slot with some clearance.

Inventors: GROSSMANN HORST, JACKSON BRIAN KENNETH
Applicants: BLACK & DECKER INC, BLACK & DECKER INC.
Application year: 1989
Main classification: B23D49
IPC codes: B23D61, B23D49, B23D51