HANDLE FOR PRUNING SAWS

Abstract: A handle (2) for hand saws with elongated toothed saw blades comprises a rear gripping part (3) and a front fastening part (4) to which the saw blade can be connected with one end. The gripping part (3) connects to the fastening part (4) via a transition part (6) which is narrower than the fastening part, causing a lower portion (4') of the fastening part to extend below the transition part to define a concave recess (7) with a depth basically corresponding to the normal width of a human second finger, thereby locating an imaginary straight line extension of the tooth line (5) of the saw blade to the region between the second and third fingers of the gripping hand.

Description: Handle for pruning saws Field of application This invention concerns a handle for handsaws with elongated toothed saw blades, comprising a rear gripping part and a front fastening part to which one end of the saw blade is fastened as an extension of the fastening part. 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. A gardener or operator in a vineyard or orchard will daily be faced with different tasks and situations. Sometimes the trees, vines, bushes or similar which are to be pruned will allow easy walking along the ground and have uncomplicated branch systems with easy access to individual branch. In other cases he may be forced to ascend high or irregularly grown branch systems, perhaps with aid of a ladder, if individual branches are less accessible. Individual branches may in one instance be thin and easily cut, in other instances thick and tough or sclerified and thus difficult to cut. 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 trappe-: in the border zone between the saw blade and the cut surfaces, thereby making the sawir.-. 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 if 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 abrasive skin injury to the skin of the palm. On previously known handles for pruning saws, the gripping part and the fastening parts merge directly into each other, forming a basically arcuate handle with a relatively small angle between the parts. A consequence of this is that the wrist must be held at an anatomically stressing angle, leading in turn to muscular fatigue and to a reduction in the force that can be transferred to the saw blade. Through the absence of a pronounced border between the gripping part and the fastening part the operator also runs a risk of the hand slipping forward from the gripping part to touch the sharp teeth of the saw blade. Purpose and features of the invention The present invention aims at circumventing the disadvantages mentioned for previously known saw handles, and to create a new improved handle. One basic aim of the invention is thus to create a saw handle which with its corresponding saw blade will be an ergonomically well-proportioned unit for 'the purpose of allowing efficient sawing for a long time without premature fatigue of the operator. One further aim is to create a saw handle which reduces every tendency to rotate the handle in the fist without abrasive injury to the skin. Still another aim is to create a handle which in a reliable way minimizes the risk of contact between the fingers of the hand touching the sharp teeth o: the saw blade. According to the invention, at least the basic aim is fulfilled with the features mentioned in characterizing part of claim 1. Other preferred embodiments of the invention are defined in the dependent claims. Brief description of the figures Among the figures, figure 1 is a side view of a saw with a handle according to the invention, figure 2 is an enlarged perspective view showing only the handle, figure 3 is an enlarged cross-section at A-A of figure 1, specifically through a fastening part of the handle, figure 4 a cross section at B-B through the gripping part of the handle. Detailed description of a preferred embodiment of the invention The pruning saw shown in figure 1 comprises an elongated blade 1 and a handle marked 2 as a whole. This handle comprises a gripping part marked 3 and a fastening part 4 to which the saw blade is connected. The blade 1 has a tooth line 5, with a multitude of separate, homologous and equidistant teeth. The saw blade itself, which is newly developed and object of a separate patent application, is with one exception technically independent of the handle of the present invention, which can be generally used for various hand saws. The exception is the cutting angle, defined as the angle between the rear cutting edge of an individual tooth and a plane at right angles to the longitudinal direction of the saw blade, and in the actu: 1 .: case this is in the region of 8 to 14 degrees. The shape of the saw handle according to the invention is the result of comprehensive practical testing. These tests have among other things revealed that the slope angle λ of the gripping part 3 is vitally important for the ergonomy of the saw and that this angle is also dependent on the cutting angle of the saw teeth. The angle λ, defined as an acute angle between aimaginary straight-line extension of the tooth line 5 and a geometric central line through the elongated gripping part, should according to these tests be in the region of 40 - 55 degrees, preferably 47 - 53 degrees. In the shown embodiment the angle λ was chosen as 48 degrees. With this slope angle the symptoms of fatigue of the operator are minimized, and at the same time the saw blade can be axially reciprocated with optimal force. This applies not only to rearward movement of the saw blade in the main direction with steeply sloping aggressive cutting edges active, but as well to the opposite direction when less steep and less aggressive edges are activated. The optimal slope angle of the gripping part depends on the cutting angle of the rear cutting edges, with the angle λ increasing when the cutting angle decreases, and reversely. It has been shown that the sum of the actual cutting angle and the actual slope angle λ should be approximately 60 degrees. If then the cutting angle is 8 degrees the slope angle λ of the gripping part should be 52 degrees, if the cutting angle is increased from 8 to 14 degrees, the slope angle should be decreased from 52 to 46 degrees. Another feature of importance for the total ergonomy of the saw is the location of the hand in relation to the tooth line of the saw blade. The saw will work most smoothly if an imaginary straight line extension of the tooth lin hits the hand somewhere between the second and third fingers. In that way the line of action of the force along the extension o the tooth line will be located centrally in the forearm of the operator. For this reason the present invention has a handle where the gripping part 3 connects to the fastening part 4 via a transition part 6 which is narrower than the fastening part 4. In this way, a concave contour recess 7 is formed on the underside of the transition pan 6, axially located behiπ.: a lower downward extension 4' from the fastening part 4. The underside of this lower extension is directed as a straight line extension of the tooth line 5. By making the reces. 7 basically as deep as the width of a normal second finger, the extension of the tooth lin will pass through the region between the second and third fingers of the hand. The lower extension 4' of the fastening part will then also act as finger protector to ensure that the fingers of the hand do not slide forward onto the sharp teeth of the blade when the saw is pushed forward. According to a preferred embodiment of the invention the gripping part 3 of the handle has an oval or elliptic cross section, as shown in figure 4, tapering towards the upper transition part 6. The gripping part is made with both the major and minor axes of the cross section successively decreasing towards the transition part from maximum values somewhere in the free lower half of the gripping part. The major axis of the elliptic section should be in the same plane as the saw blade in order to get a maximal stiffness in the sawing force direction. The oval shape also effectively prevents any tendency for the gripping part to rotate in the hand. According to a second preferred embodiment of the invention, the handle 2 is made as one continous body comprising two integrated component bodies of different polymer materials. The handle shown in figures 2 and 4 thus comprises a main body part 8 of a strong impact-resistant polymer with smooth surface. Polyamide can be advantageously be used for this main body part, which, as is seen from a comparison of figures 2 and 4, continues through not only through the fastening part 4 but also through the major length of the gripping part 3, though mainly in its interior. The other body part is a cover body 9 which encloses and protects that portion of the main body part 8 which is located in the gripping part 3. This cover body 9 can in practise be made from a thermoplastic polymer with a softer consistency than the polyamide as well as with a coarser surface structure than that. As is shown in figures 1 and 2, the cover body 9. visualized as a dotted area, ends at a front limit 10, the lower end of which is localized between the deepest pan of the recess " and an imagined straight line extension of the lower edge of the fastening part 4. The coarse and soft cover body 9 will thus end some distance away from the bottom of the recess, which ensures that the inside of the second finger will have a non-slipping contact with the coarse outside of the cover body, while the outside of the second finger will touch the smooth exposed surface of the main body part 11 in the recess and rear part of the lower extension 4' of the fastening part. This way, the inside of the second finger will have a good frictional contact with the gripping part, and the outside will be protected from rubbing contact that could lead to abrasive injury. Not only the second finger but all fingers except the thumb will then cooperate efficiently in the main sawing direction, when the saw is pulled rearwards. The fastening part of the handle is provided with a forwardly open slot 11 into which the rear end of the saw blade can be inserted. Two holes 12 for screws 13 are made in the lateral parts on each side of the slot. As shown in figure 1 the holes are diagonally off-set. Thereby the distance between the holes is maximized within the axially limited space along the fastening part. In each hole, there is a collar-shaped portion between the slot and two wider outer portions of the holes, the collar defining a narrow central hole for the screw 13. Each screw 13 interacts with a nut 14. When the screw is tightened in the nut, the saw blade 1 is clamped in the slot. The length of the screw 13 is less than the total length of the hole 12 between its opposite mouths. This leaves empty spaces on each side of the screw, usable as seats for clasps to hold the saw in a sheath, not shown in the figure. Advantages of a handle according to the invention A handle according to the invention has several advantages compared to conventional saw handles.. The rather steep slope 40-55 degrees of the gripping part relative to the fastening part allows the user to apply his hand in an ergonomically advantageous position. The handle can transfer an optimal force from the hand to the saw blade with minimal loss of energy. It ensures that the wrist will keep a comfortable angle to the lower arm. allowing longer continous use by the operator. The recess between the lower extension of the fastening part and the gripping part proper allows an advantageous location of the second finger relative to both the coarse surface of the gripping part and the sharp teeth of the saw blade. The location of the fingers relative to the saw blade and the teeth is appreciated by the operator as feeling well balanced. Restricting the line of action of the force to pass between the second and third fingers will lead to its being centrally located in the lower arm. The recess in the transition part between the gripping part and the fastening part also forms an efficient knuckle protector. The combination of two materials in the handle also means that the inside of the palm has a good frictional contact with the handle with no risk of abrasive skin injury on the outside of the finger. The oval cross section of the sloping and somewhat tapering gripping part ensures a safe and comfortable grip, and the chosen slope angle of the gripping part makes it easier to release the saw from a sheath. As pointed out earlier, the saw handle according to the invention may also be used with saw blades of other types than that shown in figure 1.

Claims: CLAIMS 1. Handle for hand saws with elongated toothed saw blades (1), comprising a rear gripping part (3) and a front fastening part (4) onto which the saw blade can be connected as an extension of the fastening part., characterized in that the gripping part (3) connects to the fastening part (4) via a transition part (6) which is narrower than the fastening part, whereby a lower portion (4') of the fastening part extends below the transition part and defines a concave recess (7) with a depth basically corresponding to the thickness of a human second finger, thereby orienting a straight line extension of the tooth line (5) of the saw blade through the region between the second and third fingers of the gripping hand. 2. Handle according to claim 1, characterized in that the gripping part (3) forms an acute slope angle (λ) with an imaginary central axis through the fastening part (4), of the order 40-55 degrees, preferably 47-53 degrees. 3. Handle according to claim 2, to be connected to a saw blade (1) the teeth of which have rear cutting edges with a cutting or rake angle in the range 8-14 degrees, characterized by the sum of the actual cutting angle of said edges and the actual slope angle (λ) between the gripping and fastening parts (3,4) being equal to 60 degrees. 4. Handle according to any of the preceding claims, characterized by the gripping part (3 ) having oval or elliptic cross-section and tapering towards said transition part (6), with both the major and the minor axis of the elliptical cross-section successively getting reduced length from a maximum in the region of the free lower half of the gripping part towards the region of said transition part. 5. Handle according to any preceding claim, characterized by the handle is made as two integrated component bodies (8,9) from different polymer materials, both a main body- part (8) of a strong and impact-resistant polymer with a smooth surface, such as polyamide, and a cover body (9) of a thermoplastic polymer with a coarser surface, enclosing and protecting that portion of the main body part which is located in the gripping part. 6. Handle according to claim 5, characterized by the cover body (9) ending at a front limit (10) located in the region between the bottom of the recess (7) and an imaginary straight line extension of the underside of the fastening part (4) to ensure a good friction grip contact between the inside of the second finger and the coarse surface of the cover body, and to let the outside of the second finger rest against the smooth surface of the main body part in the bottom region of the recess. 7. Handle according to any previous claim, characterized by the fastening part (4) being provided with a forwardly open slot (1 1) for insertion of an end portion of the saw blade (1), and that both lateral parts on each side of the slot have through holes (12) for fastening elements (13), where at least one of the holes has greater axial length than the length of the fastening element to form recessed seats between the mouths of the holes and the ends of the fastening elements, to receive clasps to hold the saw to a sheath. 8. Handle according to claim 7, characterized by the two holes (12) being diagonally offset relative to the longitudinal axis of the fastening part.

Inventors: BAECKMAN STURE, ERIKSSON ECKHARD, LUND NILS-ERIK, BAECKMAN, STURE, ERIKSSON, ECKHARD, LUND, NILS-ERIK
Applicants: BAECKMAN STURE, ERIKSSON ECKHARD, LUND NILS ERIK, SANDVIK AB, BAECKMAN, STURE, ERIKSSON, ECKHARD, LUND, NILS-ERIK, SANDVIK AB (PUBL)
Application year: 1998
Main classification: A01G3
IPC codes: A01G3, B23D51, B27B21