Field of the Invention This application pertains to a saw arbor formed by a splined mandrel slidably mated within a splined saw blade mounting sleeve. Additional splines on the sleeve's outer circumference mate within corresponding splines in a saw blade eye. This yields a balanced, precision tolerance cutting unit which minimizes wear on the saw blade, mandrel and sleeve, while improving sawing accuracy.

Background of the Invention

United States Patent No. 3,516,460 Thrasher discloses a saw arbor having a plurality of circumferentially spaced, parallel, outwardly projecting semi-cylindrical splines. A circular saw blade having a saw eye cut to match the arbor's cross-sectional shape is slidably mounted on the arbor. As the arbor is drivingly rotated, the spline's leading edges tend to make point contact with the lower forward corners of the corresponding semi-circular cutouts in the saw eye. This significantly increases wear on the eye, and can ruin the saw blade well before the saw teeth themselves wear out. The arbor's splines also wear at an increased rate, as do the bearings which support the rotating arbor. Further, the saw blade tends to flutter at high speed, resulting in a wider kerf and increased wear on the saw teeth. All of these factors contribute to an increased need for saw blade changes, which is an expens- ive, labour-intensive operation with attendant loss of lumber production.

Involute-splined saw arbors were developed to overcome the foregoing problems. Involute splines have substan¬ tially flat forward, rearward and top faces. Gear cutting techniques are used to maintain the arbor's splines paral¬ lel to the arbor's longitudinal axis. As a result, instead of making mere point contact with the saw blade eye, an involute-splined arbor achieves land contact across sub¬ stantially the entire forward face of each spline. This

significantly reduces wear, saw flutter, etc. Further, because the arbor's splines are highly parallel to the arbor's longitudinal axis, the tolerance between the arbor and the saw blade eye may be reduced in order to further reduce wear, flutter, etc.

Prior art saw arbors were of one-piece construction, with the saw blade being mounted over splines formed in the arbor itself. Modern saw arbors have a mandrel on which a cylindrically-apertured sleeve is slidably mounted, with the saw blade being mounted over splines formed around the sleeve's outer circumference. One or two longitudinally extending keyways are machined into the sleeve's aperture. The mandrel has a similar keyway. The keyways are aligned and a steel key is placed in the aligned keyways to posi- tion the sleeve relative to the mandrel.

Such arbors are subject to a number of problems. First, the keyway machining process removes material from the mandrel and from the sleeve. The weight of the removed material is not precisely offset by the key steel driven into the keyway. This results in rotational imbalance, which can degrade sawing accuracy when the arbor and saw blade are driven at high rotational speeds.

A further problem arises upon heat treatment of an arbor having a keyed mandrel and sleeve. In particular, such arbors tend to assume an oval (i.e. out of round) cross-sectional shape following heat treating. If the arbor is out of round, then the saw blade eye cannot be formed to achieve a minimum tolerance, orientation-indepen¬ dent, fit on the arbor. Saw blade eyes are conventionally formed using laser cutting techniques. In theory, the laser cutting process can produce a saw eye which will fit over any arbitrarily shaped arbor with minimum tolerance. However, in practice, a saw blade eye produced in this fashion can be mounted on the arbor in only one orientation in order to achieve the minimum tolerance aforesaid. In other orientations the saw eye either will not fit over the

arbor at all, or else it fits too loosely, resulting in increased wear, loss of sawing accuracy, etc.

Modern sawmills typically employ many circular saws, each of which undergo frequent saw blade changes. It would be highly impractical to maintain, for each arbor, a separate inventory of blades having eyes machined to fit only that one arbor; and/or to take the time to orient a saw blade's eye to achieve minimum tolerance fit in the one orientation on the one saw arbor for which that blade's eye was formed. Accordingly, in practice, circular saw blade eyes are formed to a loose tolerance, which may be no better than about 0.007" to 0.015" (0.178 mm to 0.381 mm) . This loose tolerance allows the sawmill workers to fit any blade on any arbor without regard to orientation of the saw eye relative to the arbor. However, a necessary conse¬ quence is increased wear and sawing inaccuracy, as dis¬ cussed above.

A further problem is that heat generated by the laser cutting process hardens the saw blade beyond the acceptable Rockwell hardness threshold. Consequently, after the saw eye is laser cut, the saw blade must be heat treated to reduce its Rockwell hardness. But, the heat treating process unavoidably distorts the shape of the saw blade eye. This is another reason why saw eyes are conventional- ly laser cut to tolerances of no better than about 0.007" to 0.015" (0.178 mm to 0.381 mm) . If the saw eye were cut to a closer tolerance then distortion introduced during the heat treating process might prevent the saw blade from fitting in any orientation on any arbor. The present invention eliminates keyways in the splined portions of the arbor; and, minimizes clearance between the saw eye and arbor, irrespective of which saw blade is selected for which arbor, irrespective of the orientation in which a saw blade is mounted on an arbor, and irrespective of distortion introduced by heat treating processes.

Summary of the Invention

In accordance with the preferred embodiment, the invention provides a saw arbor formed of a mandrel and a cylindrically apertured sleeve. Radially spaced splines are provided around the mandrel's outer circumference and around the inner circumference of the sleeve aperture. The mandrel splines and the sleeve aperture splines are shaped and sized for slidable mating inter-engagement. Radially spaced splines are also provided around the sleeve's outer circumference. The sleeve outer circumference splines are shaped and sized for slidable mating engagement with further splines spaced radially around a saw blade eye.

Preferably, equal numbers of equally spaced involute splines are provided around the mandrel, around the inner circumference of the sleeve aperture, around the sleeve's outer circumference and around the saw eye. The splines can be formed to achieve 0.001" (0.0254 mm) tolerance engagement between the mandrel and the sleeve, and between the sleeve's outer circumference and the saw blade eye, thus providing a high precision cutting unit.

Brief Description of the Drawings

Figure IA is a partially fragmented front elevation view of a mandrel constructed in accordance with the preferred embodiment of the invention. Figure IB is a side elevation view of the Figure IA mandrel.

Figure 2A is a cross-sectional front elevation of a saw blade mounting sleeve slidably engageable over the mandrel of Figures IA and IB. Figure 2B is an end view of the Figure 2A mounting sleeve.

Figures 3A and 3B are similar to Figures 2A and 2B respectively, but depict a mounting sleeve having a larger outer diameter than the mounting sleeve of Figures 2A and

2B. Figure 4 is an oblique perspective illustration of a mandrel, saw blade mounting sleeve and saw blade according to the invention.

Figure 5 is an oblique perspective illustration of an assembled saw arbor (with saw blade) according to the invention.

Figures 6A and 6B respectively depict portions of a prior art saw blade and a saw blade according to the invention, to compare the blades' tooth face contact.

Figures 6C and 6D respectively depict portions of a prior art saw blade and a saw blade according to the invention, to compare the blades' stiffening characteris- tics.

Figures 6E and 6F respectively depict portions of a prior art saw blade and a saw blade according to the invention, to compare the blades' tooth form characteris¬ tics. Figures 6G and 6H respectively depict portions of a prior art saw blade and a saw blade according to the inven¬ tion, to compare the blades' tooth finish. In each Figure, an encircled portion of one tooth is shown on a greatly enlarged scale.

Detailed Description of the Preferred Embodiment

Figures IA, IB, 4 and 5 depict a mandrel 10, one end 12 of which is tapered for mating engagement with a rotational support bearing (not shown) . A keyway 14 is machined into the opposite end 16 of mandrel 10 for key- fitted engagement of mandrel 10 with a powered drive shaft (not shown) which rotationally drives mandrel 10 about its longitudinal axis 18. A first plurality of straight, parallel, outwardly projecting involute splines 20 are spaced radially around the central, outer circumference 21 of mandrel 10.

A separate sleeve 22 (Figures 2A, 2B, 4 and 5) is provided. Sleeve 22 has a central, cylindrical aperture 24 having an inner circumference 26. A second plurality of straight, parallel, inwardly projecting involute splines 28 are spaced radially around inner circumference 26, as best seen in Figure 2B. Sleeve 22 also has an outer circumfer-

ence 30 around which a third plurality of straight, paral¬ lel, outwardly projecting involute splines 32 are radially spaced.

Mandrel splines 20 and sleeve aperture splines 28 are respectively shaped and sized for slidable, mating engage¬ ment of mandrel splines 20 within sleeve aperture splines 28 to form an arbor, as seen in Figure 5. Outer sleeve splines 32 are respectively shaped and sized for slidable, mating engagement of splines 32 within a fourth plurality of inwardly projecting involute splines 34 spaced radially around the eye 36 of a saw blade 38.

Preferably, equal numbers of splines 20, 28 and 32 are provided in each of the first, second and third pluralities aforesaid. Thus, a variety of different sleeves can be provided, one such example being depicted in Figures 3A and 3B in which reference numerals corresponding to those adopted in Figures 2A and 2B are utilized, with the addi¬ tion of the suffix "a". A comparison of Figures 2A, 2B, 3A and 3B will reveal that sleeves 22, 22a have the same internal diameter 40, 40a but have different outer diam¬ eters 42, 42a. Further comparison reveals that the number of internal splines 28 on sleeve 22 equals the number of external splines 32 thereon; and, that the number of internal splines 28a on sleeve 22a equals the number of external splines 32a thereon. Both sleeves 22, 22a have equal numbers of internal splines 28, 28a. Thus, either one of sleeves 22, 22a can be slidably mounted on mandrel 10 as aforesaid.

By maintaining equal numbers of equally spaced splines 20, 28, 32, 34 on mandrel 10, sleeve 22 and saw blade 38 the invention facilitates mounting of sleeve 22 in any orientation on mandrel 10; and, mounting of saw blade 38 in any orientation on sleeve 22. It is not necessary to align any particular one of splines 20 with any particular one of splines 28 in mounting sleeve 22 on mandrel 10; nor is it necessary to align any particular one of splines 32 with any particular one of splines 34 in mounting saw blade 38

on sleeve 22. Different (or even multiple) sleeves can easily be mounted on mandrel 10. By using gear cutting techniques to produce splined mandrel 10, splined sleeve 22 and splined saw blade 38, manufacturers can carefully control precision, slidable fitting of these components to achieve a tolerance of .001" (0.0254 mm).

The invention enables a sawmill operator to maximize the lifetime of mandrel 10, sleeve 22 and saw blade 38. A prior art sleeve containing a keyway can be mounted on a mandrel in only two 180° opposed orientations. However, sleeve-mandrel combinations manufactured in accordance with the invention can be inter-mounted in a number of orienta¬ tions equal to twice the number of mandrel splines (i.e. any of splines 20 can be oriented adjacent any of splines 28; and, sleeve 22 can be mounted on mandrel 10 in either one of two 180° opposed orientations) . Similarly, saw blade 38 can be mounted on sleeve 22 in a number of orien¬ tations equal to twice the number of splines 28 on sleeve 22. The absence of any keyways in sleeve 22 dramatically reduces susceptibility of sleeve 22 to deformation during the heat treating process. Mandrel 10 also has much reduced susceptibility to heat treatment distortion, because end 16 of mandrel 10 containing keyway 14 is not heat treated. Only the portion of mandrel 10 bearing splines 20 is heat treated. The effect of heat treatment distortion on saw blade 38 can also be dramatically reduced by laser cutting eye 36 to an initial size smaller than the desired final size, then heat treating saw blade 38 to reduce its hardness, and then using internal gear cutting techniques to form eye 36 in the desired final size, with splines 34.

Saw blades produced in accordance with the invention provide greater total tooth face contact than do prior art saw blades. For example, Figure 6A depicts a portion of a typical prior art saw blade having 23 teeth (i.e. suitable for mounting on a 6" (152.4 mm) diameter arbor). Each

tooth of the prior art blade has a face contact region "C" measuring 0.280" (7.112 mm). The prior art blade's total face contact over all 23 teeth is thus 23 x 0.280" = 6.44" (163.576 mm) . By contrast, an equivalent saw blade con- structed in accordance with the invention (i.e. suitable for mounting on a 6" (152.4 mm) diameter arbor and having the same tooth pitch as the prior art blade) may, as shown in Figure 6B, have 35 teeth with the face contact region "C" of each tooth measuring 0.188" (4.775 mm) , yielding a total face contact over all 35 teeth of 35 x 0.188" = 6.58" (167.132 mm) .

Saw blades produced in accordance with the invention have more radially spaced teeth and splines than equivalent prior art saw blades. For example, Figure 6D depicts a portion of a 35 tooth saw blade produced in accordance with the invention, having an eye with 35 splines. Figure 6C depicts an equivalent prior art saw blade having 23 teeth and having an eye with 23 splines. One notional radial "stiffening" line "S" extends from the center of each saw blade eye, for each one of the saw blade's spline-tooth pairs. A saw blade's radial stiffness is improved by increasing the number of such notional stiffening lines. The prior art blade of Figure 6C has only 23 such notional stiffening lines which are radially spaced at 360°/23 ^*■*** 15.65° intervals, whereas the saw blade of Figure 6D has 35 such notional stiffening lines spaced at 360°/35 = 10.29° intervals.

As shown in Figure 6F, the eye of a saw blade produced in accordance with the invention can be formed to leave a datum gap "G" above each sleeve spline 32 when saw blade 38 is mounted on sleeve 22. The datum gaps serve as a refer¬ ence for centering saw blade 38, particularly when blade 38 is removed from the arbor and mounted in a grinding machine (not shown) . As shown in Figure 6E, prior art saw blades have no corresponding datum reference, so it is not poss¬ ible to accurately center a prior art saw blade in a grinding machine. This is problematic because as the blade

is used, different portions of the saw blade eye wear unevenly. Consequently, when a worn prior art saw blade is mounted in a grinding machine, the lack of an accurate blade centering reference typically results in eccentric mounting of the blade on the grinding machine and conse¬ quential inaccurate, eccentric grinding of the saw blade's teeth. By contrast, a saw blade produced in accordance with the invention can be mounted on a grinding machine to leave an equal portion of each datum gap "G" visible above the tops of the grinding machine's blade mounting splines. Datum gaps "G" thus provide a reference circle for accu¬ rately, centrally aligning the saw blade on the grinding machine (the grinding machine typically will not have an accurately machined saw arbor of the type disclosed here- in) .

Figure 6F also illustrates the way in which datum gaps "G" can be formed by rounding the lower trough portion of each spline 34 cut into saw blade eye 36. This is advan¬ tageous in that a conventionally machined spline has sharp corners "C" as shown in Figure 6E. Sharp corners "C" tend to promote cracking of the saw blade.

As previously explained, saw blade eyes are typically laser cut. Besides hardening the saw blade as explained above, the laser cutting process presents two further problems. First, the laser cutting process leaves a minute serrated edge as seen in the enlarged circled region of Figure 6G. In prior art saw blades the serrated edge tends to abrade the saw arbor during normal sawing operations. However, in the present invention, the saw eye is only initially cut by a laser process. The subsequent gear cutting operation which machines the saw eye to its final dimensions "cleans up" the eye by removing the aforementioned serrated edge, leaving a smooth, less abrasive surface as seen in Figure 6H. Second, because the laser cutting beam must invariably be directed at an angle relative to the work piece, a tapered or bevelled edge is left by the laser cutting process, as can also be seen in

the enlarged circled region of Figure 6G. The tapered or bevelled edge contributes to small but potentially signifi¬ cant alignment errors and promotes wearing as the saw blade is driven at high speeds. The aforementioned gear cutting process also eliminates the tapered or bevelled edge, leaving a much flatter surface which is less prone to alignment errors, wearing, etc.

As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this inven¬ tion without departing from the spirit or scope thereof. For example, although splines 20, 28, 32, 34 are preferably involute splines, they may instead be straight-sided or other shaped splines, including serrations. Involute splines are preferred because they provide the aforementioned advantages of land contact and because concentrically rotatable parts inter-mounted with involute splines are self-centering. Accordingly, the scope of the invention is to be construed in accordance with the sub- stance defined by the following claims.