EP1948383A1

EP1948383A1 - Grinding wheel for a cutting chain

Info

Publication number: EP1948383A1
Application number: EP06799726A
Authority: EP
Inventors: Lennart Nilsson
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-10-28
Filing date: 2006-10-04
Publication date: 2008-07-30
Also published as: EP1948383A4; SE0502389L; CN101291766A; WO2007050006A1; SE529347C2

Abstract

The invention relates to a grinding wheel arranged for simultaneous grinding of a cutting link's cutting tooth (6) and the associated depth limiter (7) in a cutting chain, the grinding wheel comprising a circular disc-shaped body (2) having a cen¬ tral bore (3) by which the grinding wheel is mountable to a shaft driven for rotation, the grinding wheel further having a first grinding surface (4) which is effective for grinding a cutting edge of the cutting tooth, the first grinding surface being applied circumferentially on one side of the grinding wheel and near the periphery thereof, characterized by a second grinding surface (5) associated with the first grinding surface and effective for adjustment of the height of the depth limiter (7), said sec¬ ond grinding surface being arranged to face radially outwards on the opposite side of the grinding wheel at a distance within the periphery of the grinding wheel which sets a difference in height (Δh) between the cutting tooth and the depth limiter, said second grinding surface having an axial length corresponding at least to the cutting tooth's potential grinding length (L), and said second grinding surface additionally running concentrically about the grinding wheel axis (A) to extend, in relation to the shaft, in a direction which secures the maintenance of the height difference (Δh) between the cutting tooth (6) and the depth limiter (7) in spite of the decreasing height of the cutting tooth during grinding, wherein said direction is determined by the inclination which is applied to the axis (a) for grinding the subject cutting tooth, with respect to an outer plane (O) of the subject cutting tooth.

Description

TITLE

Grinding wheel for a cutting chain

TECHNICAL FIELD

The present invention refers to a grinding wheel for cutting chains, and more closely to a grinding wheel that is arranged to be driven in rotation and which is designed for grinding, simultaneously, the cutting tooth of a cutting link as well as the cutting link's depth limiter in one single operation.

BACKGROUND AND PRIOR ART

Cutting chains or saw chains of different types are known from varying fields of application, such as in motor chainsaws, mobile saw mills, tree cutting units and tree harvesters, e.g. The general structures of the chains are the same, comprising chain links which are pivotably interconnected to form an endless, flexible chain. In addition to complementary connecting links (outer links), the chain also comprises drive links (guide bar links) which are structured to be engaged by a drive wheel effective for driving the chain around the guide bar, as well as cutting links each of which alternately include a left or a right cutting tooth and a depth limiter in cooperation therewith. The chain links are interconnected by means of rivet pins going through the links, and around which the links are pivotable in a plane coincident with the guide bar.

The cutting chains are driven at high speed and provide a high cutting capacity, and are subjected to wear at various rates. Sharpened cutting teeth at accurately grinded angles are critical and important for the cutting capacity of the cutting chain, as is the chain's feed rate which depends mainly on the difference in height between the cutting tooth and the depth limiter. When this height difference is too small, the cutting depth and milling capacity decreases resulting in over-speeding of the chain and chain saw device. When the height difference is too large, the feed rate becomes aggressive which increases the risk of the chain getting jammed in the wood, resulting in kick-back of the guide bar and the chain rotating thereabout, out from the saw cut. As grinding of the chains' cutting tooth results in a decrease of the height of the same, it is of critical importance that the height of the depth lim- iter is accurately adjusted to the new height of the cutting tooth during grinding.

Grinding of cutting chains is accomplished manually by the use of files, or in machine tools having rotary grinding wheels. A drawback which is common to conventional manual techniques and grinding machines is, however, that adjustment of the height of the depth limiter to the height of the grinded cutting tooth is accomplished in a separate and subsequent operation. It is therefore difficult to ensure an optimized height difference between the cutting tooth and the depth limiter, requiring an accurate setup and control of this subsequent operation.

SUMMARY OF THE INVENTION

The present invention aims to avoid this drawback associated with conventional techniques and grinding tools. The object is met through a grinding wheel structured as defined through the characterizing features of appended claims.

Briefly, by the present invention there is provided a grinding wheel arranged for simultaneous grinding of a cutting link's cutting tooth and the associated depth limiter in a cutting chain, the grinding wheel comprising a circular disc-shaped body having a central bore by which the grinding wheel is mountable to a shaft driven for rotation, the grinding wheel further having a first grinding surface which is effective for grinding a cutting edge of the cutting tooth, the first grinding surface being applied circumferentially on one side of the grinding wheel, near the periphery thereof. A characterizing feature of the grinding wheel is that a second grinding surface, effective for adjustment of the height of the depth limiter, is associated with the first grinding surface. The second grinding surface is arranged to face radially outwards on the opposite side of the grinding wheel, at a distance within the periphery of the grinding wheel which sets a difference in height between the cutting tooth and the depth limiter. The second grinding surface has an axial length corresponding, at least, to the cutting tooth's grinding potential. It is additionally suggested that the second grinding surface runs concentrically about the grinding wheel axis to extend, in relation to the axis, at a direction which secures the maintenance of the height difference between the cutting tooth and the depth limiter in spite of the de- creasing height of the cutting tooth during grinding, wherein said direction is determined by the inclination which is applied to the shaft for grinding the subject cutting tooth, with respect to a sloping outer plane of the cutting tooth.

Preferred embodiments of the grinding wheel according to the invention are defined in subordinated claims.

SHORT DESCRIPTION OF THE DRAWINGS

The invention is more closely explained below with reference to the accompanying, diagrammatic drawings, wherein

Fig. 1 shows the grinding wheel of the invention in a perspective view, applied towards a cutting link for grinding the cutting edge of a cutting tooth;

Fig. 2 shows the grinding wheel of fig. 1 in a side view, applied towards the cutting link for simultaneous grinding of the cutting tooth and the depth limiter;

Fig. 3a-3c are sectional views of embodiments of the grinding wheel, and

Fig. 4 is a sectional view of a peripheral area broken away from one embodiment of the grinding wheel according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to fig. 1 , a grinding wheel 1 is illustrated to comprise a circular, discshaped body 2 having a central bore 3 by which the grinding wheel is mountable to a shaft which is driven for rotation in a machine for grinding cutting chains.

Machines for this purpose are known per se, and will for this reason only be given a general explanation herein: such machines typically comprise rollers for mounting of the chain, feed means for feeding the chain link by link, means for fixation of the chain in a grinding position, drive means for rotation of the grinding wheel, as well as control means by which the grinding wheel may be applied to the cutting links and by which the grinding wheel may be shifted sideways for alternately grinding left and right cutting teeth. These machines are typically equipped with two grind- ing wheels mounted at separate positions for grinding of the cutting tooth in a first operation, and for grinding of the depth limiter in a subsequent operation.

On a first or front side thereof, the grinding wheel 1 comprises a first grinding surface 4 which runs circumferentially near the periphery of the grinding wheel and which is effective for grinding the cutting edge of the grinding tooth, as illustrated in figs. 1 and 2 of the drawings. Typically, the grinding surface 4 runs in the plane of the grinding wheel for grinding a straight edge in the cutting tooth. The cutting edge runs inclined relative to a longitudinal direction D of the cutting chain, at an inclination amounting to one or some tens of degrees, such as within 15-40 degrees, typically in the order of about 30 degrees. Upon grinding, the grinding wheel is applied with a corresponding angular offset of its axis of rotation A, and more specifically, alternately from opposite sides of the direction D for grinding of left and right cutting teeth, as illustrated in fig. 1 through reference signs AR and AL, respectively.

With reference to fig. 2, the grinding wheel 1 is illustrated to comprise a second grinding surface 5 effective for height adjustment of the depth limiter. Said second grinding surface 5 is arranged on that side of the grinding wheel which is opposite from the first grinding surface, the second grinding surface facing radially outwards at a radial distance r within the periphery of the grinding wheel. The distance r determines a height difference Δh between the cutting tooth 6 and the depth limiter 7. The second grinding surface 5 has an axial length at least corresponding to a potential grinding length L of the cutting tooth.

As is best seen in figs. 2 and 4, the cutting tooth 6 is formed on a cutting link 8. The depth limiter 7 rises above the cutting link, in front of the cutting tooth 6 as seen in the operative cutting direction P of the cutting chain. The clearance between cutting tooth and depth limiter provides a space for wood chips separated by the cutting edge 9 of the cutting tooth, the cutting edge being formed in a front or leading edge of the cutting tooth as seen in the direction P. The cutting tooth 6 has a height which decreases from the cutting edge 9 towards the aft or trailing edge 10 of the cutting tooth, providing in other words an outer side or plane O which slopes towards the cutting chain from the cutting edge to the trailing edge. In figs. 2 and 4 this slope is illustrated through an angle α which defines, in this description, an angle between the cutting tooth plane O and a normal N from the cutting link. The angle α, as well as the cutting edge's inclination relative to the normal N, is significant for the feed of the cutting chain into the wood in the direction of the normal. The said inclination, i.e. the cutting angle, is determined through the inclination applied to the grinding wheel, in this description referred to as an angle β relative to the normal N. As used herein, "applied inclination" refers to the inclination applied to the grinding wheel and its axis upon grinding, and which is required in order to form the accurate cutting angle of the cutting tooth's cutting edge. The angles α and β can vary from one type of chain to the other, as for the β-angle in the order of a few degrees to some ten degrees, such as from about 3 to 30 degrees relative to the normal N. The α-angle typically amounts to a value higher than 90 degrees but lower than 120 degrees, typically from about 93 to 105 degrees. The in-feed depth is limited through the depth limiter, the upper or outermost end of which slides on the bottom of the saw cut, in this way preventing further feeding of the cutting tooth into the wood. The height difference Δh between cutting tooth and depth limiter usually amounts to one or some tenths of millimetres, typically about 0.4-0.7 mm, whereas the optimal height difference may not be the same for different types of chains or chains for different purposes.

From the above it will be understood that each grinding operation of the cutting tooth 6 results in a reduction of the cutting tooth's length L, as seen in the longitudinal direction of the saw chain, as well as a reduction in height of the cutting tooth. Accordingly, the depth limiter needs grinding with each grinding of the cutting tooth in order to maintain a constant difference in height Δh between the cutting tooth and the depth limiter.

In order to ensure a consistent height difference Δh between the cutting tooth 6 and the depth limiter 7, notwithstanding the reducing height of the cutting tooth upon grinding, the second grinding surface 5 is formed not only at a distance within the periphery of the grinding wheel, but is also arranged to run concentric with the grinding wheel axis A and in a direction relative to said axis, said relative direction being determined from the inclination which in grinding is applied to the axis A with respect to the sloping plane O of the cutting tooth. In a typical case, wherein the first grinding surface 4 is flat in the front face of the grinding wheel and thus transverse to the axis A, this relation may be defined by a generatrix G in the second grinding surface 5 intersecting the front face of the grinding wheel, or the first grinding surface 4, at an angle θ which is determined by an angle α between the cutting tooth plane O and a normal N from the cutting link, reduced by the angle of inclination β relative to the said normal N, which during grinding is applied to the grinding wheel or to the first grinding surface 4.

In view of the sloping angle of the cutting tooth plane and the applied inclination of the grinding wheel and grinding wheel axis, this relation may for one saw chain require that the second grinding surface 5 being formed to run concentrically about the grinding wheel axis as a straight cylinder. For other saw chains, this relation may result in a second grinding surface 5 formed to run concentrically about the grinding wheel axis as a truncated cone having a base facing towards the grinding wheel, or formed to run concentrically about the grinding wheel axis as a truncated cone having a base facing from the grinding wheel. Theses embodiments are illustrated in figs. 3a, 3b and 3c, respectively.

Fig. 4 shows a partial section of one embodiment of a grinding wheel according to the invention, structured for simultaneous grinding of cutting tooth and depth lim- iter in commercially available saw chains for power saws. The grinding wheel of this embodiment comprises a disc-shaped body 2 made in metal, having an outer diameter of about 150 mm, a maximum thickness axially of about 10 mm, and having first and second grinding surfaces 4 and 5, respectively, formed by ceramic material applied in the form of coatings. Application of the ceramic coatings on the metal body may be accomplished according to conventional methods for producing grinding or cutting tools. The grinding wheel of this embodiment preferably has grinding surfaces 4, 5 made of cubical boron nitride applied to a metal disc body 2.

For the subject typical saw chain, the height reduction of the cutting tooth which is related to the axial length of grinding, and the angle of inclination applied to the grinding wheel for producing the correct cutting edge angle, lead to the arrangement of a second grinding surface 5 according to the embodiment of fig. 3b. In this embodiment, a generatrix in the second grinding surface intersects the grinding wheel front face by an angle θ of 73 degrees, whereby the angle of inclination (cutting edge angle) β applied to the grinding wheel is 20 degrees and the inclination α of the cutting tooth plane O is 93 degrees, as related to the normal N. The radial distance at which the second grinding surface is arranged inside the periphery of the grinding wheel, as well as its axial extension and position on the back side of the grinding wheel, are determined individually for each type of saw chain. In this determination, account shall be taken for the original heights of cutting tooth and depth limiter, as well as a prescribed height difference between the two. No specific guidance for the individual adaptation will be given in this description, except for the explanation above regarding the determination of the axial extension of the second grinding surface relative to the grinding wheel's axis or plane. In this connection it also needs to be pointed out, that the significance of the earlier mentioned side shift of the grinding wheel with respect to the longitudinal direction D of the saw chain is reduced, when the radius of the grinding wheel is increased. If appropriate, the side shift may be compensated geometrically through a corresponding increase of the angle θ.

Claims

1. A grinding wheel arranged for simultaneous grinding of a cutting link's cutting tooth (6) and the associated depth limiter (7) in a cutting chain, the grinding wheel comprising a circular disc-shaped body (2) having a central bore (3) by which the grinding wheel is mountable to a shaft driven for rotation, the grinding wheel further having a first grinding surface (4) which is effective for grinding a cutting edge of the cutting tooth, the first grinding surface being applied circumferentially on one side of the grinding wheel and near the periphery thereof, characterized by a second grinding surface (5) cooperating with the first grinding surface and effective for adjustment of the height of the depth limiter (7), said second grinding surface being arranged to face radially outwards on the opposite side of the grinding wheel at a distance within the periphery of the grinding wheel which sets a difference in height (Δh) between the cutting tooth and the depth limiter, said second grinding surface having an axial length corresponding at least to the cutting tooth's potential grinding length (L), and said second grinding surface additionally running concentrically about the grinding wheel axis (A) to extend, in relation to the shaft, in a direction which secures the maintenance of the height difference (Δh) between the cutting tooth (6) and the depth limiter (7) in spite of the decreasing height of the cutting tooth during grinding, wherein said direction is determined by the inclination which is applied to the axis (a) for grinding the subject cutting tooth, with respect to an outer plane (O) of the subject cutting tooth.

2. The grinding wheel of claim 1, wherein the second grinding surface (5) runs concentrically about the grinding wheel axis (A) in the form of a straight cylinder.

3. The grinding wheel of claim 1, wherein the second grinding surface (5) runs concentrically about the grinding wheel axis (A) in the form of a truncated cone, a base of which faces towards the grinding wheel.

4. The grinding wheel of claim 1, wherein the second grinding surface (5) runs concentrically about the grinding wheel axis (A) in the form of a truncated cone, a base of which faces away from the grinding wheel.

5. The grinding wheel of any previous claim, wherein a generatrix (G) in the second grinding surface (5) intersects the plane of the first grinding surface (4) at an angle (θ) which is determined by the angle (α) between the cutting tooth plane (O) and a normal (N) from the cutting link, reduced by the angle of inclination (β) applied to the first grinding surface (4), relative to said normal (N).

6. The grinding wheel of any previous claim, wherein the first and second grinding surfaces are formed by ceramic coatings applied to the surface of a metal grinding wheel body.

7. The grinding wheel of claim 6, wherein the first and second grinding surfaces are formed by boron nitride coatings applied to the surface of a grinding wheel body made of steel.