Cutting – Tool or tool with support – Toothed blade or tooth therefor
Reexamination Certificate
1998-11-25
2001-03-27
Watts, Douglas D. (Department: 3724)
Cutting
Tool or tool with support
Toothed blade or tooth therefor
C076S112000
Reexamination Certificate
active
06205902
ABSTRACT:
The invention relates to a method for attaching tooth bits to a body of a blade used in sawing, in which method replaceable tooth bits are attached to be immovable with respect to the blade body to an attachment point provided for each tooth bit, on the cutting edge side of the blade body, whereby mating surfaces of each attachment point receive forces exerted on the tooth bit and wherein the tooth bits are attached in such a way that their outermost point is at a distance from the outermost point of the blade body, with the result that the tooth bits protrude with respect to the attachment point and a space remains between the blade body and a workpiece.
The invention further relates to an arrangement for attaching the tooth bits to the body of the blade used in sawing, which arrangement comprises attachment points provided in the blade body for replaceable tooth bits, to which points the tooth bits are arranged to be attached, whereby the mating surfaces of the attachment points are arranged to receive forces exerted on the tooth bits and wherein the tooth bits are attached in such a way that their outermost point is at a distance from the outermost point of the attachment point, with the result that the tooth bits protrude with respect to the blade body, and a space remains between the blade body and a workpiece.
Sawmills, various sawing machines and the like employ circular saws, in which separate tooth bits effecting the actual cutting, generally made of harder and more wear-resistant material than the blade body, are arranged on the outer circumference of the blade body of said circular saw. The tooth bits are in general made of hard metal, ceramic material or some other appropriate material. The blade body is in general tool-making steel or the like. In general, the tooth bits are attached to the body by brazing, by means of an interlocking structure, with screws, rivets, or for instance, by means of appropriate quick clamping means. Several alternative attachment methods are known, so they are not described in greater detail herein. Apart from circular saws, it is possible to employ separate tooth bits attached to the basic blade also in band saw blades and similar straight-edged blades.
However, a drawback with the prior art solutions is that when the tooth bit breaks, for instance, by the effect of a harder spot, such as a nail, stone or frozen knot, in the material to be sawn, a fragment breaking off the tooth bit causes damage also to the blade body when falling between the blade body and the workpiece. The problem is that the tooth bit in general breaks at an unpredictable or unsuitable point, and consequently the broken fragment is often of considerable size and such in shape that it causes damage to the blade body. A detached tooth bit fragment may cause damage to the blade body at the mating surface of the tooth bit or otherwise deteriorate the blade body and the attachment of a new tooth bit, which may have a consequence that no new tooth bits can be attached reliably to the blade body. So the blade body has to be discarded. In case of minor damages, it may be possible to repair the blade body by welding and grinding, but nevertheless this involves significant costs and extra work. Moreover, the properties of the repaired blade body are not necessarily equal to those of the original body any longer, in particular if the same point is subjected to repairs several times. Particularly, the interlocked tooth bits are critical with regard to the blade body damage, and they hardly allow deviations in the blade body geometry.
The object of this invention is to provide a method and an arrangement for attaching a tooth bit to a blade body, which prevents the blade body from being damaged in connection with tooth bit breakage.
The method of the invention is characterized in that the mating surface of an attachment point provided in the blade body for the tooth bit, transverse to the blade's direction of motion, is formed such that it is rearwardly oblique at its outermost part, and as a result, due to the oblique mating surface and the space, the blade body can bypass the detached tooth bit fragment without that the mating surface is damaged.
The arrangement of the invention is further characterized in that the mating surface of the attachment point provided in the blade body for the tooth bit, transverse to the blade's direction of motion, is formed such that it is rearwardly oblique at its outermost part, and as a result it is possible for the blade body to bypass the tooth bit fragment without that the mating surface is damaged.
The basic idea of the invention is that the outermost section of the mating surface, which is formed in the blade body and which supports the tooth bit in the direction of sawing, is formed oblique to the effect that the outermost parts of the blade body can bypass breaking tooth bit fragments more smoothly and easily without them causing damage to the blade body. Moreover, it is required that the tooth bit protrudes to some extent with respect to the outermost part of the attachment point allowing the tooth bit fragment to make way for the blade body safely. Further, the basic idea of one preferred embodiment of the invention is that the breakage point of the tooth bit is predetermined by providing a discontinuity to the effect that a breaking tooth bit fragment is advantageous in shape and size.
The invention has an advantage that if sawing hits a spot which is exceptionally hard and which causes damage to the blade, the expensive blade body remains intact and only a wearing part, i.e. the tooth bit, breaks. It is not a problem to replace a broken tooth bit, if the blade body remains undamaged. The price of tooth bits is low as compared with the price of the blade body, and the tooth bits have to be changed in any case every now and then, since they become dull. With the solution of the invention sawing costs can be reduced considerably, because the blade costs decrease since the blade body repair and discard can be avoided. A further advantage is that the solution of the invention can be applied to most previously known blade attachment mechanisms, its structure is simple and, moreover, it is readily manufactured. An advantage with one preferred embodiment of the invention is that when a breakage point of the tooth bit is predetermined by forming a discontinuity therein, the tooth bit breaks controllably at a predetermined point and in a predetermined manner.
REFERENCES:
patent: 4587876 (1986-05-01), Erhardt
Alston & Bird LLP
Hackman TTT OY AB
Watts Douglas D.
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