Cutting – Tool or tool with support – Rotatable type
Reexamination Certificate
1997-03-31
2001-05-15
Dexter, Clark F. (Department: 3724)
Cutting
Tool or tool with support
Rotatable type
C083S676000, C083S821000, C030S388000, C144S218000
Reexamination Certificate
active
06230600
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an arbor for mounting and driving a guided circular saw, to a circular saw adapted for use with the arbor of the invention and to a sawing machine comprising the combination of the arbor and circular saw of the invention. The invention has particular application in thin kerf sawing. The invention has application, for example, in edging machines.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 3,516,460 to Thrasher discloses a system for mounting circular saws on an arbor while allowing the saw to float axially on the arbor. The saw is guided between a pair of guides. The Thrasher saw has a scalloped eye opening that fits around an arbor having a large number of small rounded splines. The Thrasher system permits reasonably accurate thin cuts with the use of thin circular saws guided by saw guides. The use of guided saws which can “float” (i.e. which can move at least slightly longitudinally) on an arbor, while the arbor is turning, has become widely accepted in the saw milling industry.
Typical arbors for mounting and driving guided saws have 18 to 22 rounded splines and are 5 inches to 8 inches in diameter. There are standard sizes and configurations for such arbors. One problem that is now being experienced in the saw milling industry is that “standard” sized splined arbors from different manufacturers are often different sizes. This is partly due to the fact that conventional prior art arbors are very difficult to accurately machine with standard machining techniques. There are several manufacturers of saw arbors. To enable their blades to fit the arbors of all arbor manufacturers, saw blade manufacturers typically make the eyes in their circular saws oversized by as much as about 0.030 inches. The poor fit of a saw on an arbor can cause the saw to “pound” as the arbor turns. This happens despite the fact that most arbors used today have rounded splines, which, in theory, makes them self-centring to some degree. The pounding can spread the eye of the saw which makes the pounding even worse.
Another problem with prior art saws is that, unless the splines and saw are both perfectly machined, which is impossible, not all of the splines engage the eye of the saw when the saw is being driven.
Another problem experienced in saw mills is that the forces exerted on a saw by the lobes in a prior art arbor result in repeated shocks being delivered to the saw blade in a region concentrated around the eye of the saw. These problems are exacerbated because conventional arbors provide only a very small driving contact area between the arbor and a saw blade.
Some have attempted to reduce these problems by providing a more accurately machined saw and arbor which fit together to very close tolerances. This approach has not been entirely satisfactory because, with arbors of conventional design, close tolerances between saw and arbor tend to increase the likelihood that the saw will “bind” on the arbor and will not float freely along the arbor as is desired. Furthermore, it is not possible with common current techniques to cut the eye of a saw to an accuracy of better than about ±0.002 inches. Further, such arbors still provide only a very small contact area between the driving surfaces on the arbor and arbor contacting surfaces in the eye of the saw.
SUMMARY OF THE INVENTION
A first aspect of the invention provides a sawing machine comprising: a frame and an arbour pivotally mounted to the frame for rotation about a longitudinal axis of the arbor. The arbor comprises a saw mounting portion having a trilaterally symmetrical cross sectional profile. The profile defines three rounded lobes. Each of the lobes extends around approximately one third of a circumference of the saw mounting portion. Preferably each of the lobes has an end region in which the profile follows an arc of a circle centered on the axis. Each of the lobes has a leading edge portion in which the profile preferably follows an arc of a circle centered in an opposing one of the lobes. The sawing machine further comprises a circular saw mounted on the saw mounting portion for rotation with the arbor. The circular saw comprises an eye having a profile corresponding to the cross sectional profile of the arbor. A pair of guides, one on either side of the saw, keep the saw in a desired position. In one embodiment of the invention, the guides comprise collars mounted on the arbor at spaced apart locations one on either side of the circular saw. The collars and arbor leave the saw free to float slightly axially along the saw mounting portion between the collars.
Another aspect of the invention provides a circular saw comprising an eye. The eye has an internal profile which is symmetrical with respect to rotations of 120 degrees. The internal profile defines three rounded recesses. Each of the recesses extends around approximately one third of a circumference of the eye. The profile preferably follows an arc of a circle centered in an opposing one of the recesses in its parts between end portions of adjacent recesses.
Yet another aspect of the invention provides an arbor for mounting and driving a circular saw. The arbor comprises a saw mounting portion having a trilaterally symmetrical cross sectional profile. The profile defines three rounded lobes. Each of the lobes extends around approximately one third of a circumference of the saw mounting portion. Each of the lobes has a leading edge portion. In the leading edge portions of each lobe, the profile preferably follows an arc of a circle centered in an opposing one of the lobes.
In a preferred embodiment the profile follows an arc of a circle centered on a longitudinal axis of the arbor in end portions of the lobes. Preferably the arbor comprises a shaft extending through a bore of a sleeve bearing the saw mounting portion.
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Dexter Clark F.
Oyen Wiggs Green & Mutala
Precision Arbor Systems, Inc.
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