GB2154505A - Cutting tool - Google Patents

Abstract

A hand saw having cutting teeth 22 with a depth limiting features compatible with the forces capable of being generated by an operator. The leading cutting edge of each tooth is followed by a rearwardly sloping bottom surface 26 that allows the operator to control the bite of the teeth and thereby produce a smoother cutting action. Each tooth 22 is provided with a front surface 24 having a concave configuration as shown in Figures 5 and 7. <IMAGE>

Description

SPECIFICATION Cutting tool The invention relates to a cutting tool for cutting wood, for example, for pruning trees and shrubs and for carpentry applications.

Hand-held cutting tools are mostly of two basic types, namely hand-held knives and hand-held saws. The basic designs of such knives and saws are similar in that each has an elongate blade provided with a handle at one end. The operation of each is basically also similar in that the blade is drawn back and forth across the desired cutting line while pressure is applied on the blade by a pivotal urging of the operator's wrist. The cutting actions, however, are quite different. The knife employs a continuous cutting edge and slices through, and thereby separates, the material being cut, whereas the saw has teeth that individually bite into and remove bits of material thereby digging a trench, or kerf as it is commonly called.

The smooth precise cutting action of a knife is highly desirable but for many applications the knife is simply unsuitable. For example, consider a large tree limb. The sharp edge of the knife blade will easily slice into the wood but only to a very shal low depth. As the blade enters the cut, the cut has to widen. Wood is "elastically" compressable (more or less, depending on the type of wood) and thus penetration is effected by compression of the wood fibres by the sides of the blade to thereby enlarge the cut. However, as more of the blade is forced into the cut, the cumulative effect of the resistance by the wood to this compression very quickly renders it very difficult for the operator to continue cutting.

The hand-held saw, having its blade edge made up of a sequence of sharp points, (referred to as teeth) cuts a trench that allows free entry of the blade. Typically, the cutting action of the saw involves a drawing of the saw blade coupled with forward pivoting of the wrist to achieve penetration of the teeth. The teeth dig in and pull loose in a rapidly repetitive action, and in the process, wood particles are ripped or torn loose from the wood member. As the saw teeth are worked back and forth in the cut, the trench is deepened until the desired severing of the wood member is accomplished. This cutting action will be herein referred to as stutter cutting.

A major problem with use of the saw blade is that at least in start up, the stutter cutting makes it difficult to hold the blade on the desired line of cut.

This difficulty is referred to as the saw's tendency to skate and is a major cause of minor accidents experienced by operators who place their off hand too close to the desired line of cut. Also, the cut is ragged, the cutting efficiency is poor, and using the saw is an uncomfortable and often a difficult task for the operator. These problems can be aleviated by reducing the space between the teeth, in depth and length, but to do so limits the ability of the saw to remove the cut particles of wood and this undesirably effects the cutting capabilities of the saw.

The present invention accordingly provides a cutting tool for cutting wood and wood materials, the tool comprising a blade having a cutting edge formed by cutting teeth spaced apart by gullets, at least some of the teeth being formed with an elongate tapered bottom relief surface which controls the depth of cut.

The invention also provides a cutting tool for cutting wood and wood materials, the tool comprising a blade having a cutting edge formed by a series of cutting teeth spaced to form gullets therebetween, certain of the teeth having a front surface and a bottom surface co-opeatively formed for controlled depth cutting of the wood material, the front surface and bottom surface intersecting to form a leading cutting edge having a leading cutting point, the bottom surface being inclined inwardly relative to the blade from the cutting edge to form a limiting surface whereby penetration of the cutting ppint into the wood material is limited to a controlled depth.

The invention can be embodied as a saw wherein the cutting action substantially departs from that of typical stutter cutting of existing saws and approaches more closely the slicing action of a cutting knife, without materially affecting cutting capability, because the cutting teeth are designed to penetrate to a controlled depth and to substantially retain that depth to slice away wood chips rather than tear out wood particles. With little or no wrist pressure, the point of the teeth are limited to a very shallow depth that is ideal for start up. As a kerf is established, increased wrist pressure achieves increased depth of penetration, bigger bites, and more rapid cutting, all while substantially eliminating the undesirable characteristics of stutter cutting.

The invention is further explained below by way of example with reference to the accompanying drawings, in which: Figure 1 is a side view of a pull type pruning saw embodying the invention; Figure 2 is a view on a larger scale of a portion of the pruning saw of Figure 1; Figure 3 is a sectional view on lines 3-3 of Figure 2 showing a cutting tooth of the saw; Figure 4 is a sectional view on lines 44 of Figure 3 showing a cutting tooth on the other side of the saw; Figure 5 is an underneath view on a larger scale of part of the pruning saw, taken on lines 55 of Figure 1; Figure 6 is a schematic front view of a cutting tooth of the saw, on a still larger scale, as it enters a wood member in a start up mode; Figure 7 is a side view of the cutting tooth shown in Figure 6;; Figure 8 is a front view of the cutting tooth shown in a full cut mode; and Figure 9 is a side view of the cutting tooth shown in Figure 8.

Illustrated in Figure 1 of the drawings is a pruning saw 10 having an elongate blade 12 to which a handle 14 is attached at one end. The saw 10 is a pull type saw, meaning that it is designed to cut as the blade 12 is being pulled over and through a limb 16 as indicated by arrow 18. The forward or push motion of the saw 10 is simply a return motion with little or no cutting taking place. The invention is however, readily embodied in push type saws in which the cutting teeth are reversed. In general, the sawing action comprises gripping of the handle 14, and while drawing the blade in the direction of arrow 18, urging the handle in a forward pivotal motion as indicated by arrow 20 for urging the blade 12 into the limb 16.

It will be understood that the cutting edge of the blade 12 comprises a series of cutting teeth 22 better shown in Figures 2-5. Each cutting tooth 22 has a front surface 24 and a bottom surface 26, which co-operatively produce the controlled cutting function previously described. The tooth configuration is completed by a surface 28 which, together with the front surface 24 of the following tooth, forms a gullet 30, that is the relief for removal of wood chips as is further explained in the part of the description below headed 'Operation".

As will be apparent from Figure 3, 4, and 5, the teeth 22 are bent outwardly from the side of the blade 12, alternately, first to the right side and then to the left side of the blade. This bending is a combination of bending and twisting to force the bottom surface 26 outwardly at an angle "a" (Figure 5) relative to the side of the blade. This being locates the point 32, which is the intersection of the outside edges of the surfaces 24 and 26, as the outermost point of the tooth 22. This outward positioning of point 32 is typically referred to as the "set" of the saw.

The front surface 24 is formed, as by grinding, to have an angle "b" (Figure 5) relative to the length of the blade. Use (primarily in production) of a round abrading surface such as a grinding wheel with a rounded edge or a round or circular section file 34 produces the desired hook shape illustrated in Figure 2. The bottom surface 26 is also angled inwardly from its outer side edge as by grinding to form an angle "C" (Figure 3) and is further angled inwardly relative to its leading edge to form angle "D" (Figure 2). The edge formed by these angles "b" and "C" will be hereafter referred to as the limiting edge and the bottom surface 26 will be referred to as the limiting surface.

Specific dimensions The dimensions of a specific pruning saw which has been produced and used and which demonstrates the advantages of the present invention, will now be described.

A blade was blanked from 1075 steel having a thickness of 0.108 cms (0.425 inches). The blade was 26.035 (10.250 inches) long with a height varying from about 4.445 cms (1.750 inches) at the handle to about 2.731 cms (1.0750 inches) at the opposite, or distal, end. The blade was slightly concave with a radius of about 140 cms (55 inches). These dimensions are typical of pruning saws and other dimensions and configurations typical of pruning saws will easily suffice.

The saw was provided with 25 cutting teeth with notches or "gullets" formed 0.635 cms (.250 inches) deep. One side of the notch was on a radial line (relative to the concave curvature) which ultimately forms the front surface 24, and the other side of the notch was at a 35 degree angle therefrom and forms the rear surface 28 of the preceding tooth. The length of the bottom surface 26 was about 0.635 cms (.250 inches) and the tooth was twisted to form angle "a" by setting the point 32 outward from the side of the blade a distance of 0.0508 cms (.020 inches). The front surface 24 was formed with a round file 34 having a diameter of about 0.198 cms (.078 inches), set out at an angle "b" of 30 degrees. The top surface 26 was ground with a side angle "C" of 30 degrees and a length angle "D" of about 4 degrees.

Operation The operation of a hand-held saw of the present invention is illustrated in the schematic drawings of Figures 69. Figures 7 and 9 show only one of the cutting teeth but it will be appreciated that a preceding or following cutting tooth on the other side of the saw blade 12 will operate in a similar manner.

Figures 6 and 7 illustrate a cutting tooth 22 in a start up mode. With very little pressure applied to the blade, the point 32 is maintained at a shallow depth by reason of the resistance generated by the penetration of the tooth, indicated by width x ei d length y, which dimensions increase as the tooth ie forced into the limb 16. With this shallow penetration, the tooth 22 merely scratches the wood surface at a consistent depth and stutter cutting is avoided. Starting the cut on a desired cutting line is thus easily achieved.

After several passes of the saw blade 12, a sufficient depth is achieved to confine the blade in the cutting line and additional pressure car be safely applied, by pivotal pressure in the direction of the arrow 20 applied by the operators hand and wriss The increased pressure will increase the de?th of cut as illustrated in Figures 8 and 9. However, by appropriate design and referring specifically to the angles "C" and "D", the resistance dependent on the dimensions x and y is rapidly built up and restricts the amount of penetration that can reasonably be applied by the operator. Thus a balance is achieved whereby the drawing force to move the blade in the direction of the arrow 18, which is needed to pull the point 32 through the wood, does not exceed the operator's ability to hold the teeth in the cut. The result is a steady and smooth cutting action, whereby wood chips 36 (Figure 9) are stripped from the limb 16.

Although the invention is not to be in any way limited by this theory, it is believed that the cutting control that is achieved is largely a result of the elastic compressability of wood fibres. As the cutting edge of the tooth 22 takes its bite, the wood tries to partially fold back behind the cutting edge where it engages the limiting edge of the tooth.

The greater the bite the greater this engagement and in the same manner as described for the ac tion of a knife, resistance to such further penetration quickly builds up and offsets the forces tending to bury the cutting tooth. The unrestricted "digging in" of the prior cutting teeth are believed to be the primary cause of stutter cutting. This is supported by the relatively smooth cutting action that is achieved by the saw of the present invention.

The wood chips (and the wood particles in prior saws) have to be carried out of the kerf and thus a sufficient gullet 30 (the relief area formed by the notch) has to be provided. Experience teaches that a notch 0.635 cms (.25 inches) deep is desirable for this reason. Also, it has been found that the curved front surface 24 is beneficial in directing the flow of the chips 36 away from the cutting point 32.

Modifications It will be understood that different types of wood present different degrees of resistance to cutting difficulty and thus a more or less agressive cutting tooth than herein described may be desirable. The agressiveness of the tooth is varied by changing the angles "a", "b", "C" and "D".It has been found that acceptable ranges for these angles are: angle "a" between 30 and 6O; angle "b" between 250 and 40 ; angle "C" between 0 and 45 ; and angle "D" between 10 and 70 (The desired angle "C" is greatly affected by the width of the blade and a very narrow blade used in soft wood will permit the 0 angle configuration.) The length of the tooth can be changed as well in that only a relatively small portion, the dimension y of Figures 7 and 9, is utilized for limiting penetration. However, as the blade is repeatedly resharpened with file 34, this length is gradually shortened and thus the life of the saw is affected by shortening the length of the tooth.

Whereas the invention has been found to be most beneficial to hand-held wood cutting saws, this is believed to be due to the particular properties of wood, the slow cutting motion and power limitations inherent in manual cutting, and the design of manual saws which dictate the application of that power. Other forms of cutting tool for operation under similar conditions might very well ben efit from the embodying of the invention thereon, and the scope of the invention is not limited to the embodiment specifically described and shown but by the following claims.

Claims (9)

1. A cutting tool for cutting wood and wood materials, the tool comprising a blade having a cutting edge formed by cutting teeth spaced apart by gullets, at least some of the teeth being formed with an elongate tapered bottom relief surface which controls the depth of cut.

2. A cutting tool for cutting wood and wood materials, the tool comprising a blade having a cutting edge formed by a series of cutting teeth spaced to form gullets therebetween, certain of the teeth having a front surface and a bottom surface co-operatively formed for controlled depth cutting of the wood material, the front surface and bottom surface intersecting to form a leading cutting edge having a leading cutting point, the bottom surface being inclined inwardly relative to the blade from the cutting edge to form a limiting surface whereby penetration of the cutting point into the wood material is limited to a controlled depth.

3. A cutting tool as claimed in claim 2 wherein the bottom surface is inclined inwardly within a shallow angular range from 10 to 7 .

4. A cutting tool as claimed in claim 2 or 3 wherein the front surface of the certain cutting teeth is rearwardly inclined side-to-side relative to the blade to form with the bottom surface a rearwardly inclined side-to-side cutting edge with the forward point of the cutting edge forming the leading cutting point, the cutting teeth being offset to project the cutting point outwardly from the side of the blade and with some of the certain cutting teeth having cutting points on one side of the blade and others of the certain cutting teeth having cutting points on the other side of the blade to cut a kerf wider than the width of the blade.

5. A cutting tool as claimed in claim 4 wherein the cutting edge angle ("b") is in the range of 250 to 400 from the blade, and the cutting teeth are angularly offset relative to the blade by an angle ("a") in a range of 3" to 6".

6. A cutting tool as claimed in claim 4 or 5 wherein the rearward angle ("b") of the front surface is formed by means of a round abrading surface to provide the cutting tooth with a hooked configuration.

7. A cutting tool as claimed in any one of claims 2-6 wherein the bottom surface is inclined inwardly side-to-side from the outer edge thereof to form a limiting edge that controls penetration of the tooth into the wood material.

8. A cutting tool as claimed in claim 7 wherein the side-to-side angle ("C") of the bottom surface is in the range of 0 to 450,

9. A cutting tool substantially as herein described with reference to the accompanying drawings.