This invention relates to band saw blades and, particu¬ larly, to saw blades having an irregular configuration which are especially adapted for use in large band saw machines for cutting very hard metal work pieces of large cross-sectional size. In commercial band saws, an endless saw blade is looped about a pair of wheels by which it is driven, and approximately midway between the wheels of the band saw, a pair of pressure guides are located, which are spaced apart a distance greater than the cross-sectional size of work pieces to be cut by the machine. These guides apply pressure to the back edge of the blade as the sawtooth edge cuts through the work. In most of the commercially available band saws, the cutting edge of the blade and the back edge are parallel and follow straight lines. As the teeth of the blade cut through the work piece, all teeth in contact with the work have an equal, albeit, minimum force applied thereto. This causes the blade to bow outwardly from the work and there is a tendency for each tooth not to cut a full chip. Cutting efficiency of such blades is, thus, rela¬ tively slow, particularly when cutting very hard metal work pieces and blade life is quite short.

In the Tapley Patent No. 4,195,543 granted on April 1, 1980, a band saw blade is disclosed which has an overall sinu¬ soidal pattern, that is, both the cutting and back edge of the blade follow a wavy pattern. The Tapley Patent refers as background to a number of prior patents which also disclose blades having undulating configurations. These include U. S. Patent No. 286,706 to Kay; U. S. Patent No. 817,361 to Brown;

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ϋ. S. Patent No. 1,850,478 to Schaefer 1932 which show con¬ tinuous band saws for use in cutting soft materials such as meat. Canadian Patent No. 883,602 to Amada 1971, is also referred to in Tapley as disclosing a sinusoidal band saw, having convexly curved hard portions and concavely curved soft portions. In Amada, the wave length of their blade pattern is made approximately one inch. Tapley distinguishes configuration of his blade from those of the above-mentioned prior art by characterizing the prior art blades as having varying wave lengths adapted for cutting soft material, while Tapley's blade has a longer wave length adapted for cutting hard material.

There are a number of other patents in the prior art wherein the sawtooth edge of the blade is straight and the back edge of the blade is progressively tapered relative to the cutting edge. These include: German Patent DT2,748,822 dated March 5, 1978, which shows a band saw having progressively tapered sections with cam step from the portion of the blade of maximum thickness to the next adjacent section of minimum thickness. U. S. Patent No. 4,160,397 dated July 10, 1979 to Bertini discloses a saw blade in which the back edge includes oppositely inclined portions which taper in opposite directions from an intermediate point on the blade. The inclined edges are sloped to diverge outwardly relative to the cutting edge of the blade from one intermediate point. U. S. Patent No. 4,205,571 dated June 3, 1980 to Bertini discloses a band saw blade in which the rear edge is progressively inclined relative to the

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cutting edge and the minimum and maximum transverse sections of the blade are contiguous and define a cam step between the inclined sections of the back edge of the blade.

It is the principal object of this invention to provide an improved band saw blade, having improved cutting speed and longer wear and is particularly advantageous for use in cutting large metal work pieces.

It is another object of this invention to provide an improved band saw blade of the above type, which is relatively more economical to manufacture since about fifty percent of the back edge of the blade need not be modified from that of a con¬ ventional band saw blade.

It is also an object of this invention to provide a band saw blade of the above type for use in band saw machines having pressure guides spaced apart on opposite sides of the work wherein the guides cooperate with the patterned back edge of the blade to effect a variable cutting action, whereby the blade cuts the work alternately at one angle and then at a substantially different angle.

The above and other objects and advantages of this invention will be more readily apparent from the following description and with reference to the following drawings, in which:

Figs. 1-5 are elevational views of a schematic nature

showing a band saw blade of a type embodying this invention, illustrating its variable cutting action.

Referring, in detail, to the drawings in Fig. 1 is shown a band saw blade 8 of the type embodying this invention. The blade is shown cutting a work piece w which has its longi¬ tudinal axis disposed transversely of the cutting plane of the blade. The blade is an endless band looped about a pair of rolls and is driven thereby. In the drawings, the blade is shown moving from right to left as Illustrated by the arrow a.

A pair of saw guides are illustrated at 10 and 12, which are spaced apart a distance greater than the cross- sectional size of the work which the band saw machine is adapted to cut. These guides are pressed against the back edge 14 of the blade by any suitable means and in this way, the blade is continuously urged against the work w.

Blade 8, embodying this invention, comprises a straight cutting edge 16 and a patterned back edge 14. The cutting edge of the blade 8 may be of conventional toothed construction wherein the teeth lie along a straight line. The back edge 14 of the blade is of stepped or tiered construction and includes recessed edge portions 18 and outer edge portions 20, which are not recessed. The outer edge portions 20 are preferably the unmodified back edge of a conventional band saw blade in which the cutting edge and back edge of the blade are straight and parallel. To fabricate a blade of the type embodying this

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invention, it is only necessary to machine the recessed portions 18 of the back edge of a conventional band. This is more economical than fabricating a band saw wherein the entire back edge of the blade is progressively tapered oveτ the length of the blade.

The blade 8 includes tapered or inclined back edge por¬ tions 22 and 24, which extend from the outer edge portions 20 to the recessed edge portions 18. Preferably, the major portion of the back edge 14 is composed of the recessed straight edges 18 and the outer straight edges 20, which are both parallel to the cutting edge of the blade. The inclined edge portions 22 and 24 are only a minor portion of the length of the blade and serve as a smooth transition for the saw blade guides 10 and 12 as the blade moves thereagainst. In one specimen of blade embodying this invention, as illustrated in Fig. 4, the length b of each recessed edge was made 9 inches and the length c_ of the outer edge 20 also 9 inches. The leading inclined edge 22 was about 3 inches, as shown at d in Fig. 5; and the trailing inclined edge 24, as illustrated at e_ in Fig. 5, was also about 3 inches. The depth of the recessed portions was about .045 inch, although this could vary from .010 inch to .125 inch. It will be recognized that the lengths of the parallel edge portions are many times greater than the lengths of the inclined edge portions. In addition, the length of the outer edge portion £ plus the inclined section e_ equals the length of recessed sec¬ tion b plus inclined edge d. Preferably, therefore, in a blade

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e bodying this invention:

c + e_ ^■**** b + d_

In addition, the saw guide spacing, i.e., the distance between the guides 10 and 12 is preferably equal to the length of one of the parallel edges plus the length of a tapered edge. In the embodiment described above, the saw guide spacing was 12 inches, the parallel edges 9 inches, and each inclined edge 3 inches.

Referring now in sequence to Figs. 1-5, it will be noted in Fig. 1 that saw guide 10 is shown positioned against the leading end of edge 20 and guide 12 is correspondingly located at the beginning of edge 18, the blade 8 moving from right to left in the drawing. Since the guides urge the blade against the work w, the blade will be tilted relative to the horizontal angle -Θ-. In Fig. 2, the blade continues to move with the guides, urging the blade 8 at the same cutting angle. This cutting angle will be held for approximately the next 9 inches of blade travel. In Fig. 3, the blade has advanced until guide 10 is now against the recessed edge 18, while guide 12 is against the outer edge 20 of the blade. As illustrated in Fig. 3, the blade angle, relative to the horizontal, has now shifted as illustrated at $ in Fig. 3. It will be recognized that in Fig. 1 for angle -&-, the blade centerline Is above the horizontal plane while in Fig. 3, It has shifted below the hori¬ zontal to define the angle 0.

In Fig. 4, the blade has moved over the next 9 inches

of blade travel and in Fig. 5, the blade cutting angle has shifted back to the same cutting angle as illustrated in Fig. 1.

It will be realized that one saw guide is riding on one parallel surface 18 or 20 at the same time the other guide is riding on the other of these two parallel surfaces. With this blade arrangement, the blade alternately cuts at two different angles relative to the work piece. In this way, the number of teeth of the blade in contact with the work at any one time is reduced whereby the pressure exerted by each tooth is increased and each tooth, therefore, takes a better cut than is the case where the saw is maintained at the same cutting angle as it advances through the work piece.

To evaluate the cutting action, a blade embodying this invention was used to cut a 304 stainless steel 4" diameter bar. The band saw was operated at a band speed of 120 SFM. Thirty- five cuts were made. The 6th cut took an elapsed time of 3.10 min. and the 35th cut 4.05 in. An average cutting time of 3.66 min. was achieved.

The identical work piece was cut with an equivalent saw blade but having a progressively tapered back edge, as described in U. S. Patent No. 4,160,397. The same machine speed and all other parameters of the test described above were duplicated. In this test, the best cutting time achieved was 3.97 min. and the 35th cut took 6.27 min. An average cutting speed for the thirty-five cuts was 5.38 min. This represents approximately a

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32% improvement in average cutting speed of a blade embodying this invention as compared with a band saw blade in which the back edge is progressively inclined in opposite directions rela¬ tive to the cutting edge. A blade embodying this invention was also compared with a conventional band saw of the identical metal and tooth design and was found to have approximately a 180% improvement in cutting speed for an identical work piece.

In addition, to its outstanding performance, the blade embodying this invention is easier and more economical to manu¬ facture since only about one half of its back edge Is machined to provide recessed portions, the remainder of the blade's back edge being that of a conventional saw blade.

Having, thus, disclosed this Invention, what is claimed is:

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