US3414029A - Knife for cutting lumber - Google Patents

Description

P. A. KIRSTEN KNIFE FOR CUTTING LUMBER 'Dec. 3, 1968 4 Sheets-Sheet 1 Filed Aug. 26, 1965 1958 P. A. KIRSTEN KNIFE FOR CUTTING LUMBER Filed Aug. 26, 196' r 4 Sheets-Sheet 2 Inventor- Dec. 3, 1968 P. A. KIRSTEN 3,414,029

KNIFE FOR CUTTING LUMBER Filed Aug. 26, 1965 4 Sheets-Sheet 5 Fig.5

Dec. 3, 1968 P. A. KIRSTEN $414,029

KNIFE FOR CUTTING LUMBER Filed Aug. 26, 1965 4 Sheets-Sheet 4 Inventor United States Patent Office 3,414,029 KNIFE FOR CUTTING LUMBER Paul Arthur Kirsten, Ernst-Moritz-Arndt-Str. 6, Renal, near Bonn, Germany Filed Aug. 26, 1965, Ser. No. 482,850 8 Claims. (Cl. 144-230) ABSTRACT OF THE DISCLOSURE A knife for use with wood cutting machines to cut strips and shavings of predetermined width comprising a body member having a bottom chip surface and a forward edge surface defined by a pair of planar surface portions disposed in parallel relation to the longitudinal axis of the knife. A plurality of parallel spaced recesses are formed in the chip surface transverse to the longitudinal axis of the body member and intersect the forward edge surface to define cutting edges therewith. The spaced recesses define splitting tips therebetween which determine the widths of the strips cut. The planar surface portion of the forward edge surface adjacent the chip surface includes the cutting edges and is disposed in co-planar relation with the cutting plane of'the knife, while the other planar surface portion is angularly disposed relative to the cutting plane to form a relief angle therebetween.

The present invention relates to an improved form of cutting knife which is particularly advantageous when used in conjunction with a disc type wood cutting machine or a cylindrical type wood cutting machine.

In the cutting of lumber in order to produce flat shavings for cellulose, veneer panels or the like, splitting and peeling knives are used whereby two cutting dimensions of the resultant wood shavings are determined. That is, the length of a wood shaving in the direction of the wood fibre is determined by the length of the splitting knives, and the thickness of such shavings is determined by the distance between the peeling knife cutting edge and the surface of the knife carrier member against which the wood engages. The influence of the pressure by which the wood is engaged against the knife carrier is not a significant factor with respect to the thickness of the wood shavings produced.

It is known in the art that the splitting knives can be eliminated by using disengaged peeling knives whereby the partial cutting edges of the preceding peeling knife are placed on the gaps of the subsequent knife. In the area of the knife gaps the shaving groove located ahead of the knife is interrupted by bridges for supporting the wood. However, with n knives of this type only the production of 11/2 solid knives is obtained. Released or disengaged peeling knives are also known where both the tooth (outer cutting circle) and the gap (inner cutting circle) are effective as peeling knives. The fact that long splinters are torn into the shaving grooves is a disadvantage in tool carriers having this type of knife, and bridges for supporting the wood cannot be utilized in such a case. If such a knife were positioned obliquely and if the slot ahead of the knife which directs the shavings into a shaving-receiving area were bridged by the length of the shaving in the direction of the fibre, poor cutting conditions would result for the splitting, because at the trailing end of the cutting edge a negative cutting angle exists. The wood fibres would not be cut through smoothly at such a location, but rather such fibres would be torn or crushed off. This disadvantage would also exist with obliquely positioned knives having rectangular recesses over their width on the side of the shaving surface.

It is also known in the art to provide knives where an open space is ground out in a sawtooth-like manner.

3,414,029 Patented Dec. 3, 1968 The tooth tips in such a case will control the splitting under favorable conditions, but such knives will not cut flat shavings parallel to the wood fibre. In order to provide for cutting parallel to the wood fibre with knives of the latter type, it has been proposed to feed the wood at such an angle that the fibres of the wood are parallel to the partial cutting edges of the knives, rather than to feed the wood so that it is parallel to the axis of the knife carrier member. There is a tendency for the wood to be milled out in a rack-like manner, and therefore each individual piece of wood placed in the machine must be maintained in a firm manner and must be fed at a predetermined speed in the longitudinal direction. The pieces of wood may have only a small diameter, since otherwise the shaft of the knife tends to become unduly long.

In addition to the foregoing, it is known to provide peeling knives having recesses over the width of the shaping surface. That is, recesses are provided over the width of the surface of the knife which forms the cutting angle gamma with the line perpendicular to the cutting direction of the cutting edge. Thus, splitting cutting edges are reduced. In order to achieve uniform thicknesses of the Wood shavings, the knife should be operated without any clearance angle. However, it has been found that such knives will not operate satisfactorily because considerable difficulty is encountered where too small a clearance angle is provided since the exposed surface becomes smeared with wood resin causing generation of heat, and the surface of the knife carrier also becomes smeared making cutting extremely difiicult. Apart from the knvies last above mentioned which are not at all satisfactory for the reasons stated, all other known knives discussed hereinabove leave tracks with each cut on the wood. The splitting knives are placed slightly above the cutting plane of the peeling knives in the case of excelsior machines or cutters of flat discs, or they are placed above the cutting cylinder in cutting machines having cylindrical type knife carriers, and in such instances the splitting knives leaves splitting indentations on the surface of the material from which shavings are being cut. Released or disengaged peeling knives and those with sawtooth-like cutting edges leave depressions corresponding to the length of the shaving or they will mill out the wood in a rack-like manner. During the succeeding cut, the corresponding knives do not always hit the same tracks again because the wood to be cut, particularly during the final phase of the cutting operation, can no longer be guided and held firmly enough, and the result is that undesirably small and fine parts are produced.

It should also be noted that certain disadvantages occur during the grinding of released or disengaged knives whose teeth split on an outer cutting circle and peel thereon, and whose gaps peel on an inner cutting circle. Such knives are always sharpened on a special machine in accordance with a plunge-cut method to produce a released cutting edge. Often unduly pronounced round surfaces are produced which cause crushing of the shavings and also increase the contents in fines, In order to eliminate such disadvantages, the invention provides that at a given thickness of the shavings to be produced, the depth of the recesses at the shaving surface of the knife is made a function of the shaving thickness, and each partial cutting edge formed by such recesses possesses at least one special exposed surface comprised of one or more parts. This exposed surface may be formed according to the invention by at least two partial exposed surfaces of various inclinations whereby in certain cases one of these partial cutting surfaces may he provided with a zero clearance angle alpha as a final grinding phase. The use of a knife of the present invention is particularly advantageous with cylindrical knife carriers because in such a situation the knife is disposed parallel to the axis of the carrier member and its partial cutting edges produce oblique cuts with respect to the direction of the wood fibres, so that the wood is fed parallel to the knife carrier axis.

Now in order to acquaint those skilled in the art with the manner of utilizing and practicing my invention, I shall describe in conjunction with the accompanying drawings certain preferred embodiments of the invention.

In the drawings:

FIGURE 1 is a front elevational view of a disc type wood cutting machine equipped with knives constructed in accordance with the present invention;

FIGURE 2 is a side elevational view of the apparatus of FIGURE 1;

FIGURE 3 is an enlarged fragmentary front elevational view of a cutting knife formed in accordance with the present invention;

FIGURE 4 is a sectional view taken along the line A-B of FIGURE 3;

FIGURE 5 is a front elevational view of an alternative embodiment of the present invention showing a cylindrical type wood cutting machine equipped with knives constructed in accordance with the invention;

FIGURE 6 is a top plan view of the apparatus of FIG- URE 5;

FIGURE 7 is an enlarged fragmentary sectional view showing the mounting of a knife on the cylindrical knife carrier of FIGURE 5; and

FIGURE 8 is a fragmentary top plan view of the apparatus of FIGURE 7.

Referring now to the drawings, FIGURES 1 and 2 show a disc type wood cutting machine having a plurality of knives 1 which are fixedly secured to a knife carrying disc 4. The knife disc 4 is rotated by a motor and rotates about an axis 55. The wood 6 to be chipped is fed by a feeding member 7 against a front surface 8 of the knife disc 4, and the wood is disposed on the bottom of a compartment 9 which extends closely adjacent to the cutting surface of the knife 1.

Referring to FIGURES 3 and 4, a knife 1 is shown clamped in fixed position to the disc 4 by means of a clamping iron 3 and a screw 2. The cutting edges of the knife, explained more fully hereinbelow, project outwardly of the front surface 8 of the disc 4 through an appropriate opening defined by edge portions 20 and 20'. The cutting edges rotate in a cutting plane 10-10 and peel or cut shavings having a thickness d in planes parallel to the fibers of the wood 6.

Each knife 1 comprises a body member having a rectangular configuration, as viewed in FIGURE 1, with the longitudinal axis of the body member being disposed in generally radial relation to the axis of rotation 5-5 of the disc 4. The knife body member has a bottom chip surface 11 and an upper surface 11 parallel to the bottom chip surface. The knife body member also has a forward edge surface defined by a generally planar first surface portion 13' and a second planar surface portion 15. The first and second planar surface portions 13 and 15, respectively, are disposed in parallel relation to the longitudinal axis of the body member, with the first surface portion 13 preferably being co-planar with the cutting plane 10-10. The second planar surface portion is preferable angularly disposed relative to the plane of the chip surface 11 so as to define a relief angle alpha between the second planar surface and the cutting plane during cutting operation. The relief angle alpha is provided to minimize the area of the forward edge surface of the knife which lies in the cutting plane 1010, thereby reducing the friction surface between the knife and the material being cut.

The bottom chip surface 11 has a plurality of parallel spaced recesses 12 formed therein, such as by milling, which recesses extend in transverse relation to the longitudinal axis of the knife body member. Referring to FIG- URE 3, each recess 12 is defined by a first wall portion disposed in substantially normal relation to the bottom chip surface 11 and a second wall portion disposed in oblique relation to the plane of the chip surface and intersecting the first wall portion at 14. The cross sectional area of each recess 12 is generally triangular in shape when considered within the envelope defined by the first and second wall portions and the plane of the chip surface 11. Preferable, the depth of each recess 12, as measured by the height of the first wall portion normal to the bottom chip surface 11, is substantially equal to the thickness d of the strips or shavings to be cut from the wood 6. The first and second wall portions intersect the planar surface portion 13 of the forward edge surface of the body member so as to define and establish cutting edges at the lines of intersection. The cutting edges of each knife 1 are thus within planar surface portion 13' and define cutting plane 1010 during operation of the cutting machine.

The parallel recesses 12 define splitting tips 13 there between, which splitting tips are spaced a distance 1 equal to the desired width of strips or shavings cut from Wood 6. The portions of the splitting tips 13 adjacent the planar surface portion 13' serve to cut the strips or shavings transversely to the direction of the fibers of wood 6 and thus determine the widths of the strips cut by the aforedescribed cutting edges of the knife.

By establishing the cutting edges of each knife 1 in the plane of planar surface 13', it can be seen that grinding of the knives 1 to maintain sharp cutting edges can be readily accomplished by one normal grinding operation over the entire longitudinal length of surface 13. Also the planar surface 15 forming the relief angle alpha with the cutting plane 10-10 can be readily ground to the desired relief angle through a continuous grinding stroke in the longitudinal direction of the knife.

-.If flat wood chips having a thickness of approximately 3 mm. are to be peeled, it may be desirable to reduce the surface area of the planar surface 13' which engages the wood 6 in frictional sliding relation. Such a reduction may be desirable where the frictional sliding surface creates excessive heat during cutting which may damage the cutter knife or reduce the life of the cutting edges. The exposed surface area 13' may be readily reduced by a grinding wheel 16 moved against the knife 1 adjacent the cutting edges defined by the oblique wall portions of recesses 12. Noting FIGURE 3, the grinding wheel 16 can be caused to remove a portion of the knife 1 to produce a relief surface 13, 17, 18, 19 generally adjacent each of theoblique cutting edges with the relief surface so produced being angularly inclined relative to said bottom chip surface and the longitudinal axis of the body member. Itwill be understood that the amount the exposed surface area 13 is reduced will be determined by the depth of cut of grinding wheel 16 as viewed in FIGURE 4. After lifting the grinding disc 16, the knife 1 is displaced by an amount equal to the length of the wood shavings 1 in the longitudinal direction, after which the next surface 13, 17, 18 is ground and so on. In order to limit the steps in the longitudinal direction of the knife, the surface 13-14 extending over the entire width of the knife may be utilized. The operation is somewhat similar to that used for the sharpening of saws, and the surfaces 13, 17, 18, 19 are somewhat inclined in their longitudinal direction against the continuous exposed surface 15. The grinding widths 13-17 and 18-19 need not be precise, as is the case in connection with plunge-cut grinding for released knives. That is, even slightly rounded edges on the grinding wheel will not have any detrimental effect. Subsequent to the sharpening operations at the exposed surfaces 15 and 13, 17, 18, 19, a fine grinding is effected in the plane 10-10 with the result that all partial cutting edges are placed precisely in the cutting plane 1010.

It is also possible without difliculty to impart upon the grinding disc 16 a width equal to the partial cutting edge length and to extend the partial exposed surfaces 13, 14, 18, 19, so produced beyond the edge 20. While such an operation comprises a plunge-cut grinding operation, it is not at such a location as to incur the disadvantages discussed hereinabove, because slight roundings as a result of a somewhat rounded grinding wheel disc will not be located at the cutting edges but rather in the exposed surface area. A subsequent fine grinding to produce a phase located in the cutting plane 10 will produce a veryuseful knife in accordance with the present invention.

FIGURES 5 and 6 show an alternative embodiment where the knives 1 of the present invention are utilized in conjunction with a cylindrical type wood cutting machine. In this instance the knives 1 are secured to a cylindrical knife carrier member 4 which is rotated by means of a motor and a clutch 50 around an axis 5. The wood 6 to be chipped is advanced by a feeding member 7' against the supporting surface 8'. Accordingly, the wood is situated at the bottom of a supporting compartment 9' which extends closely adjacent to the cutting edges of the knives 1.

FIGURES 7 and 8 illustrate a knife 1 which is secured by means of a screw 2 and a clamping iron 3 in order to fasten the knife to the knife carrier member 4. The cutting edges of the knives rotate in a cutting cylinder 1010' and peel shavings of a thickness d parallel to the wood fibre.

When used in conjunction with cylindrical knife carrier members, the knife of the present invention provides the additional advantage that at a corresponding depth t of the recesses 12 in the cutting surface 11 of the knife 1, as shown in FIGURE 8, the partial cutting edges 13-14 formed thereby assume a sloping or inclined position relative to the axis of the knife carrier member 4 so that even where the knife 1 is itself parallel to the axis there will be provided an oblique cut inclined at the usual angle delta to the direction of the wood fibre In FIGURE 8, the chip length of the wood in the fibre direction as indicated at l is equal to 25 mm., and the depth of the recesses 12 at the chipping surface of the knife as indicated at t is equal to 8 mm. The partial cutting edges 13-14 are thus provided with an oblique position to the axis of the knife carrier member, the angle therebetween being about 18 degrees, the latter being a mean value of the usual oblique cutting angles, The knife 1 is itself oriented parallel to the axis of the knife carrier as shown in FIG- URE 8 where the knife edge 2020 extends parallel to the axis 5'5'. The knife of the present invention may also be used in excelsior machines.

While I have described my invention in certain preferred forms, I do not intend to be limited to such forms except insofar as the appended claims are so limited, since modifications coming within the scope of my invention will readily occur to others, particularly with my disclosure before them.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

I claim:

1. A knife for use with wood cutting machines and the like to cut strips and shavings of predetermined width, comprising, a body member having a bottom chip surface and a forward edge surface, said bottom chip surface having a plurality of recesses formed in spaced relation therein, each of said recesses being defined by a first wall portion and a second wall portion intersecting said first wall portion, said first and second wall portions intersecting said forward edge surface so as to define cutting edges at the lines of intersection therewith, said spaced recesses defining splitting tips therebetween, said splitting tips being spaced apart a distance equal to the desired width of the strips to be cut by the knife, said forward edge surface having a generally planar first surface portion including said cutting edges and disposed in parallel relation to the longitudinal axis of said body member, and said forward edge surface further having a second planar surface portion angularly disposed relative to the plane of said chip surface so as to define a relief angle between said second surface portion and the cutting plane during cutting operation.

2. A knife in accordance with claim 1 wherein said first wall portion is disposed in substantially normal relation to said bottom chip surface and said second wall portion is disposed in oblique relation to said chip surface.

3. A knife in accordance with claim 1 wherein the depth of each of said recesses, when considered in said first planar surface portion of said forward end surface, is approximately equal to the predetermined thickness of the strips to be cut during cutting operation of the knife.

4. A knife in accordance with claim 1 wherein said first planar surface portion including said cutting edges is disposed in co-planar relation with the cutting plane of the knife during cutting operation thereof.

5. A knife in accordance with claim 1 wherein said first and second planar surface portions of said forward edge surface extend substantially the full longitudinal length of said body member.

6. A knife in accordance with claim 1 wherein said first and second wall portions define generally triangular cross sectional configurations when considered with the plane of said bottom chip surface.

7. A knife as defined in claim 6 wherein said recesses extend in parallel relation to each other transversely to the longitudinal axis of said body member.

8. A knife in accordance with claim 1 wherein said first planar surface portion of said forward edge surface is adapted for co-planar relation with the cutting plane of the knife during cutting operation thereof, and wherein said forward edge surface further includes a relief surface generally adjacent each of said cutting edges defined by said second wall portions intersecting said forward edge surface, said relief surfaces being angularly inclined relative to said bottom chip surface and the longitudinal axis of said body member.

References Cited UNITED STATES PATENTS 1,436,208 11/1922 Sprague 241240 FOREIGN PATENTS 715,294 9/1954 Great Britain. 964,827 5/ 1957 Germany. 1,166,960 6/1958 France.

FRANCIS S. HUSAR, Primary Examiner.

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