Pruning saw

Abstract: A pruning saw comprises an elongated sawblade which has a line of equal, homologous and equidistant teeth (6,6'), and where opposite sides of the blade extending between the line of teeth and the back (7) are concave. A thinnest waist (M) between the concave sides (10,10') is located closer to the line of teeth (6,6') than to the back (7) where the blade has its maximun height. Thereby the teeth get an improved vertical clearance in the kerf.

Description: Field of application of the invention This invention concerns a pruning saw of the kind as described in the preamble of claim 1, comprising an elongated saw blade, which is connected at one end to a handle and which has along its whole length a uniform line of teeth with homologous and equidistantly located teeth, where both faces of the blade between the line of teeth and an opposing back edge have a slightly concave shape and where an individual tooth has front and rear cutting edges formed by intersection of a flat face with two obliquely ground surfaces, each of which at an angle to the faces, and where an individual gullet between two teeth is rounded and extends at right angle to the plane of the faces. Background of the invention Handsaws of the type called pruning saws among craftsmen are used not only for non-professional gardening but also professionally such as for pruning of growing plants in vineyards, large fruit orchards or similar. Lately, the increasing use for such purposes has led to stringent requirements for such saws which are frequently used under various circumstances.. To fill the operators' requirements in easy as well as difficult circumstances, the saw should have a number of optimized properties. One of these is that the teeth should be efficient and allow fast cutting even of thick and tough branches, at the same time leave the cut wood surface as smooth as possible to simplify fast healing of the tree. The saw blade should have sufficient clearance to avoid getting pinched in the cut kerf. Also, the chip removal and transport out from the kerf should be efficient, otherwise sawdust tends to get trapped in the border zone between the saw blade and the cut surfaces, thereby making the sawing more difficult. Further, the shape of the saw blade should allow easy access to individual branches even in confined space. The ergonomic properties of the saw seen as a whole are also important. The saw blade and the handle should together form a harmonical unit, feeling well balanced in the hand, and able to transfer the muscular power of the operator to the saw blade and the sawn item in such a way that it is efficient and requires minimal energy. Not least important in this case is the geometric shape of the handle and its surface structure. The gripping part of the handle should thus form such an angle to the blade that the sawing will be efficient when pulling rearwards as well as when pushing forwards, at the same time allowing the operator to lastingly maintain a steady grip on the handle. Furthermore, the surface structure of the handle should have such a character that there is no tendency for the gripping part of the handle to rotate within the fist, while at the same time it will not cause superficial skin injury to the skin of the palm. Pruning saw blades of that hind are known e.g. from DE 881 421, WO8501239 or FR 1126 700. Purpose and properties of the invention Pruning saws of the type mentioned above according to prior art do not fill the needs and requirements well enough. The present invention aims to create an improved pruning saw. One fundamental aim of the invention is thus to create a pruning saw which will ensure efficient chip removal from the kerf and permit fast and efficient sawing with minimal muscle power while producing smooth sawn kerf surfaces, at the same time avoiding getting squeezed in the kerf. Another aim is to create a pruning saw which is at least to some extent operative in each of two directions of force application, pulling rearwards and pushing forwards. Another aim is to create a pruning saw with optimal ergonomic design. Aqccording to the invention, at least the fundamental aim is achieved with the properties described in the characterizing part of claim 1. Other preferred embodiments are additionally defined in the dependent claims. Brief description of the drawings Among the drawings, figure 1 is a side view of a saw according to the invention, figure 2 is a perspective view showing only the handle of the saw, figure 3 is a slightly enlarged cross section B-B in figure 1, through an attachment part of the handle, figure 4 is a cross section C-C through the gripping part ofthe handle, figure 5 is a greatly enlarged cross section A-A through the saw blade of figure 1, and figure 6 is an enlarged detail drawing showing a number of individual teeth in the line ot teeth of the saw. Detail description of one preferred embodiment of the invention The pruning saw shown in figure 1 comprises an elongated blade (1) and a handle unit (2) This handle comprises a gripping part (3) and an attachment part (4) connected to the saw blade. The blade has a line of teeth (5), which comprises a multitude of teeth (6,6') of equal shape. Preferrably, the teeth shoul have equal size and equal distance for simplest manufacture. A back edge (7) is opposite to the line of teeth (5). In the shown embodiment the back edge (7) extends straight and parallel to the line of teeth (5) from the handle to a point at a certain distance from the handle, having a maximum height here. From here the back edge (7) is somewhat curved tapering down to near the free end front region. At the front end (8) the back edge turns into a convexly rounded edge portion (9) which in its turn via a short straight portion directly turns into a front tooth (6). In other words, the saw does not have the front portion with sharp corners so characteristic of conventional pruning saws, which are likely to injure the bark of a tree when inserted between a trunk and a branch to be sawn off. The rounded edge portion (9) of the saw blade will reduce the risk of this type of bark injury. In addition, the line of teeth (5) will get a maximal length for a given blade length since the first tooth is part of the extreme front portion while the rearmost tooth is located in the immediate vicinity of the front end of the handle. In contrast to conventional set teeth, the teeth (6,6') are produced only through grinding operations from a flat blade blank as described in the following. Both opposite faces (10,10') are made with a slightly concave shape as shown in figure 5. Referring to figure 6, this shows the geometry of the individual teeth. Each tooth has front and rear edges (11,12) created by grinding of rake surfaces (13,14) each forming an acute angle with the correponding outer face of the blade, and meeting each other at a common ridge line (15). The side rake angle, measured as the angle between the rake surfaces (13,14) and the outer face should be in the range 40-50 degrees, preferrably 42-48 degrees. The optimal value is 45 degrees. The angle of attack α for the rear edge (12), measured as the angle between the edge and a plane normal to the blade or the longitudinal line of teeth should according to the invention be in the range 8 - 14 degrees. In the preferred case shown this angle of attack α is 12 degrees. The corresponding angle of attack β for the front edge (11) should be in the region 33 - 43 degrees, preferrably 36 - 40 degrees. In the preferred case shown the angle β is 38 degrees. The bottom (16) of an individual gullet between two adjacent teeth is rounded and extends at right angle to the plane of the blade. It is preferrably shaped as an almost semicylindrical surface, merging at one point (17) into a sloping surface (18) extending to the edge (11). On the other side of the gullet is a corresponding sloping surface (18'). As shown in figure 6 the sloping surface (18) has a slope γ which in the preferred case is shown as 7 degrees. The corresponding sloping surface (18') has a slope γ' which in the preferred case is shown as 5 degrees. In the preferred case illustrated by the drawings the saw blade has a maximum width or height H, shown in figure 5, at its rear portion of about 42 mm, and a thickness which varies slightly, but is of the order of 1 mm. The tooth height D measured from the gullet bottom (1) to the tip (19) of the tooth is shown as about 5 mm. The height (D1) measured from the tooth tip to the center of the semicircle of the gullet bottom is about 4 mm. In other words, the gullet bottom is formed by a cylindrical surface with radius 1 mm. Referring to figure 6 it should be emphasized that the ridge line (15) should extend all the way to where the edges (11,12) meet. This implies that the tip (19) becomes pointed and extremely sharp. It should be noticed that the gullet between adjacent teeth, because of the semicylindrical volume delimited by the bottom surface (16), has a volume which is more than three times as large as the corresponding volume at conventional saw blades. This means that the gullets will be able to hold a volume of sawdust three times larger than conventional blades. As a result the transport of sawdust out from the sawn kerf is greatly facilitated, and the tendency of the saw blade to get pinched in the kerf is radically reduced. Figuras 1 and 6 show how every second tooth is a left tooth and every second tooth is a right tooth. Every left tooth (6) has its outer surface on the left side of the saw blade when it is viewed from the handle towards the front end (8), while the outer surface of a right tooth (6') is part of the right side surface of the blade.No setting is needed. The thickness T of the blade in the tooth tip region, shown in figure 5, is in the preferred case 1,26 mm. Corresponding thickness T' at the back is 1,06 mm. Although part of these slightly concave sides, the outer surfaces of the teeth may be regarded as flat. Between the back (7) and the tooth line (5) the blade has a thin waist (M) where the thickness is least, in the preferred case 0,84 mm.A characteristic of the sawblade according to the invention is that this waist is located closer to the tooth line than to the back, at least in the the rear half where the back (7) has its maximal height. Preferrably, the distance between the back (7) and the waist M should be at least 1,3 times the distance between the waist and the tooth line. In the actual case the distance H1 between the waist and the tooth line is 17 mm when the height H is 42 mm. The smaller distance and the greater thickness change implies that the concave curvature must be more pronounced below the waist than above. On earlier known concavely ground saw blades the waist has been located approximately midway between the back and the tooth line. This has made the vertical clearance angle of the teeth non-optimal. By locating the waist according to the invention noticeably closer to the tooth line the concave shape will be more pronounced in the near vicinity of the tooth line, increasing the vertical clearance while retaining an appropriate stiffness of the back. As blanks for production of saw blades according to the invention strips of steel are used with initially rectangular cross section, where both opposing sides are flat and parallel. For saw blades with the actual height of 42 mm and maximum thickness of 1,26 mm, bands with a thickness of 1,5 mm could be used. Initially the rake faces (13,14) are produced by grinding in two steps. In a third step the gullets between adjacent teeth are ground. This is done with a grinding tool giving a generally semicylindrical narrow bottom extending normal to the plane of the blade. The center distance C between these gullets is in the illustrated case 5 mm, thus making the pitch distance between tooth tips 5 mm. The grinding operations can be done on a multitude of blanks clamped as a packet side by side. In a fourth step the sawblade is given the desired contour by blanking or shearing. The rearmost toothless portion (20) shown in figure 1 is then given a partially tapering shape suited for insertion in the handle. In this portion are also two holes (21) to take fasteners (22) as screws. As shown in figure 1 these holes are diagonally offset. This maximizes the distance between the fasteners within the restricted space of the fastening part of the handle, to minimize the force on each fastener. In a last step the side surfaces of the blades are ground to get a concave shape with very large curvature radii, where the grinding tools are applied in such a way that the thinnest section after grinding, called the waist (M), is localized closer to the tooth line (5) than to the back (7) as described above. Advantages with the pruning saw according to the invention. Compared to conventional pruning saws, the saw according to the invention has a number of advantages. Because of the geometry of the blade and its teeth, as described with figures 5 and 6, the saw will operate efficiently and fast. Because of the tooth edge angles proposed, the teeth will cut aggressively, which is further accentuated by the extremely sharp and pointed tooth tips, at the same time that the spacious and rounded gullets will ensure a good chip transport. The efficient chip transport will in its turn ensure that the saw will travel easily while cutting, with no tendency to get pinched in the kerf. The deep gullets make it easy to resharpen the saw by hand filing. Since the teeth are not set but formed only by grinding , while retaining the outside flat and smooth, which serves to create extremely even and smooth cut surfaces. This helps the healing of the cut object after trimming. Since the thin waist of the saw blade is located relatively close to the tooth line, the clearance along the tooth line will also be very advantageous, with the risk of pinching of the blade in the kerf reduced to a minimum. Through the narrowly elongated form of the saw blade, characterized by a roundedly tapering outer end and a softly rounded front contour at the free end, it is ensured that the saw can be neatly manipulated in narrowly confined spaces, at the same time limiting damage to the bark. Having the tooth line extend along the whole length of the blade, the first tooth in immediate vicinity of the free front end of the blade and the rearmost tooth in immediate vicinity of the handle, noticeably enhances the sawing efficiency.

Claims: Pruning saw comprising an elongated saw blade (1) at one end connected to a handle (2) and along its whole length having a line of teeth (5) of equal shape (6,6') where both opposite sides (10,10') of the blade between the line of teeth (5) and the opposite back edge (7) have a slightly concave shape, and where the individual tooth (6,6') has front and rear cutting edges (11,12) at the intersection between an outside (10,10') and one of two obliquely ground rake surfaces (13,14) each of which forming an acute angle to the outside, characterized by a thinnest waist (M) between the slightly concave sides (10,10') being located closer to the line of teeth (5) than to the back edge (7) where the blade has its maximum height. Pruning saw according to claim 1, characterized by the distance between the back edge (7) and the waist (M) being at least 1.3 times the distance between the waist and the line of teeth where the blade has its greatest height. Pruning saw according to claim 1 or 2, characterized by said back edge (7) at its front end (8) merging into a convexly rounded edge portion (9) which where it meets the straight line of teeth turns into a front tooth (6). Pruning saw according to any previous claim, characterized by the rear edge (12) having a vertical angle of attack (a) in the range 8 - 14 degrees and the front edge a vertical angle of attack (β) in the range 33-43 degrees Pruning saw according to any previous claim, characterized by said obliquely ground rake surfaces (13,14) meeting each other at a common ridge line (15) which extends uninterrupted to the point where the edges meet, thereby creating a sharply pointed tip (19) of the tooth.

Inventors: ERIKSSON ECKHARD, LUND NILS-ERIK, ERIKSSON, ECKHARD, LUND, NILS-ERIK
Applicants: KAPMAN AB
Application year: 1998
Main classification: A01G3
IPC codes: A01G3, B23D49, B27B21, B27B33, B23D61