# Patent

## Title
Saw blade with reduced modal frequencies in the operating frequency range

## Abstract

A saw blade is provided including a circular metal disc including a circular metal disc including a central aperture and a plurality of teeth spaced around a periphery of the circular metal disc. A first plurality of fully enclosed body slots are generally equally spaced from a center of the circular metal disc by a first distance and a second plurality of fully enclosed body slots are each disposed directly radially outward from a respective one of the first plurality of body slots. The second plurality of slots are generally equally spaced from the center of the circular metal disc by a second distance greater than the first distance. The saw blade design provides a blade with no modal frequencies in the operating frequency range.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application No. 61/437,842, filed on Jan. 31, 2011. The entire disclosure of the above application is incorporated herein by reference.


FIELD
The present disclosure relates to a method of designing a saw blade, and more particularly, a saw blade with reduced modal frequencies in the operating frequency range.
BACKGROUND AND SUMMARY
This section provides background information related to the present disclosure which is not necessarily prior art.
Circular saw blades are used for cutting various materials used in the construction trades. Circular saw blades have been made with various body slot designs. U.S. Pat. No. 4,776,251 discloses circumferential extending laser-cut slots. Each of the slots consists of an arc of a circle concentric with the body of the saw and parallel to the peripheral edge thereof. The slots are spaced in a manner such that each slot cools an area of the body when the saw blade is in operation.
U.S. Pat. No. 4,574,676 discloses a circular saw blade with a plurality of strain compensating slots. The slots include a number of inner slots extending outwardly from a central bore of the blade and a number of outer slots which are substantially parallel to the inner slots and respectively spaced therefrom in the radial direction and circumferential direction.
U.S. Pat. No. 3,981,216 discloses a high speed saw blade including a plurality of narrow expansion slots formed in the outer edge of the blade at a negative angle with respect to a line extending radially from the center of the blade to the slots. The slots are provided for noise reduction.
U.S. Pat. No. 5,555,788 discloses a saw blade including a plurality of radial expansion slots having a J-shape and a plurality of arced body slots. The disclosure states that the J-shape of the expansion slots seem to cause less high frequency whistle. The arced body slots are provided with two opposed sides of different radius which do not have its two ends in radial alignment on the blade to provide better stiffness.
While many saw blade body slot designs have been designed, the slots have been designed for cooling, strain compensating, expansion and stiffness purposes without consideration of the effects on vibration issues.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
A saw blade is provided including a circular metal disc including a central aperture and a plurality of teeth spaced around a periphery of the circular metal disc. A first plurality of fully enclosed body slots are generally equally spaced from a center of the circular metal disc by a first distance and a second plurality of fully enclosed body slots are each disposed directly radially outward from a respective one of the first plurality of body slots. The second plurality of slots are generally equally spaced from the center of the circular metal disc by a second distance greater than the first distance.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.



DRAWINGS
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
FIG. 1 is a side plan view of a saw blade design having no modal frequencies in the operating frequency range of the saw blade;
FIG. 2 is a side plan view of a saw blade design having a single modal frequency in the operating frequency range of the saw blade;
FIG. 3 is a graph showing the modal frequencies of various alternative 71⁄4′′ saw blade designs including the saw blades shown in FIGS. 1 and 2;
FIG. 4 is a graph showing the modal frequencies of the saw blades shown in FIGS. 1 and 2 for a 61⁄2′′ diameter saw blade; and
FIG. 5a is a side plan view and FIGS. 5b-5c provide detail views of a further saw blade design according to the principles of the present disclosure.



DETAILED DESCRIPTION
Example embodiments will now be described more fully with reference to the accompanying drawings.
With reference to FIG. 1, the saw blade design 10 includes a circular metal disc 12 including a central aperture 14 and a plurality of teeth 16 spaced around a periphery of the circular metal disc 12. FIGS. 1, 2 and 5 are each drawn to scale so that specific size and relationship characteristics are accurately depicted. A first plurality of fully enclosed body slots 20 are each generally equally spaced from a center of the circular metal disc 15 by a distance X1 and are generally evenly spaced circumferentially about the center, and a second plurality of fully enclosed body slots 22 are each disposed directly radially outward from a respective one of the first plurality of body slots 20. The first plurality of body slots 20 can have a width of 2 mm or less and can have a length to width ratio of between 6 and 20. The second plurality of body slots 22 are generally equally spaced from the center of the circular metal disc 12 by a second distance X2 greater than the first distance X1 and are generally evenly spaced circumferentially about the center. Each of the second plurality of slots can have a width of 2 mm or less and can have a length to width ratio of between 30 and 70. The first and second plurality of body slots 20, 22 can each terminate in opposite end portions having a diameter that is larger than a diameter of the slots at their intermediate portions. The circular metal disc 12 includes a plurality of open-ended slots 28 extending radially inward from the periphery of the circular metal disc. The open-ended slots 28 can terminate in an inner-most portion 30 having a diameter that is larger than a diameter of the slots 28 at its outboard end. As shown in FIG. 1, the inner-most portion 30 can have a circular shape, or alternatively other shapes can be used such as an oval shape 30′, as shown in the alternative embodiment of FIG. 5. The diameter of the inner most portion 30, 30′ can be approximately 4-8 mm while the width of the slot 28 can be approximately 2 mm. The saw blade 10 according to the principles of the present disclosure can have a standard diameter of for example 61⁄2, 71⁄4, 81⁄4′′, 10′′, 12′′ or can have an alternative diameter for use on various saws such as portable circular saws, miter saws, and table saws. The number or teeth on the saw blade can be a standard number such as 24 or 40, although other numbers of teeth can also be utilized.
The second plurality of body slots 22 each include a pair of arcuate end sections 22a and an undulating intermediate section 22b disposed between the arcuate end sections 22a. The number of undulations 24 provided in the undulating section 22b of the body slots 22 can be varied depending on a specific application. As shown in FIG. 1, the body slots 22 can include four undulations 24, while FIG. 5 shows the body slots 22′ having five undulations 24. It is noted that the body slots 20 and 22 can be generally concentric about the center axis of the saw blade 10. Further, as illustrated in FIG. 5c, the distal ends 25 of body slots 20, 22 can be generally circular with a diameter (d) approximately twice a width of the slots 20, 22. The distal ends 25 of the slots 20, 22 can be aligned along a common radius R, as illustrated in FIG. 5c, or offset as illustrated in FIG. 1.
The slots 20, 22, as shown in FIG. 5c traverse an angle of approximately 48°, although other angles can be used. The slots 20 can be approximately 54 mm (R1) from the blade center and the slots 22 can be approximately 83 mm (R2) from blade center for a 301 mm diameter (D) blade. The location of the first plurality of body slots 20 define the mean area of where all the modal frequencies will lie while the outer location of the second plurality of body slots determines how far apart the modal frequencies will be.
With reference to FIG. 2, an alternative saw blade design 10′ is shown in which the body slots 40 are provided with arcuate end sections 40 a and an undulating intermediate section 40 b. FIG. 2 is drawn to scale so that specific size and relationship characteristics are accurately depicted. The body slots 40 are shown as non-concentric to the center axis of the blade with one end 42 of the body slot being located in closer proximity to the axis than the second end 44. The body slots 40 are generally evenly spaced circumferentially about the center axis. As shown in the graph of FIG. 3, the saw blade shown in FIG. 2 is represented by the triangular data points represented by graph line DES1 in the frequency vs. mode diagram. The saw blade design as illustrated in FIG. 2 had a single modal frequency value that falls within the operating frequency range for the specific saw blade design. The presence of a single modal frequency provides a significant improvement in the characteristics of the blade as compared to the other samples DES3-DES5 which were tested and which have multiple modal frequencies within the operating frequency range
The operating frequency range is determined by determining a minimum and a maximum operating frequency of the saw blade and includes determining a minimum and a maximum saw blade operating revolution speed and multiplying the minimum and maximum saw blade operating revolution speeds by the number of teeth on the saw blade. The minimum and maximum saw blade revolution speeds can be in units of revolutions per second. By way of example, a saw blade having a 71⁄4′′ diameter and 24 teeth can have a minimum operating speed of 4,350 revolutions per minute. That minimum operating speed converts to a minimum operating speed of 72.5 revolutions per second which can be multiplied by the number of teeth (24) to provide a minimum operating frequency of 1,740 Hz. The same saw blade has a maximum operating speed of, for example, 5,800 RPM which converts to 96.67 revolutions per second. 96.67 revolutions per second multiplied by 24 teeth provides a maximum operating frequency of 2,320 Hz. Thus, the operating frequency range of the saw blade is between 1,740 and 2,320 Hz.
The modal frequencies of the saw blade design can be identified using a solid model design of the saw blade in a software program that determines the modal frequency values of the solid model design of the saw blade. The software is an off the shelf available software that can determine the modal frequencies of solid model components and, by way of example, can include a generative part structure analysis software commercially available as a plug-in from CATIATM. Other similar solid model analysis system software can be utilized or the modal frequencies can be determined by physical testing of a prototype blade.
The results of the analysis performed for identifying the modal frequencies includes an identification of each modal frequency (for example modes 1-8) and its frequency value for the saw blade design.
By way of example, as illustrated in FIG. 3, the modal frequencies of five different saw blade sample designs were tested for determining whether the modal frequencies fall within the operating frequency range of each sample saw blade tested. It is noted that the sample DES1 test results are illustrative of the saw blade design shown in FIG. 2 while the sample DES2 test results are illustrative of the saw blade shown in FIG. 1. The test results for samples DES3-DES5 are illustrative of alternative saw blade designs having various body slot configurations. As can be seen from graph line DES1, the sample 1 test data shows one modal frequency value of 2,163.62 Hz that falls within the operating frequency range of between 1,700 and 2,450. The graph line number DES2 which is illustrative of sample DES2 shown in FIG. 1, has no modal frequencies in the operating frequency range. Therefore, the sample DES2 saw blade, shown in FIG. 1 has no significant blade vibration during the cutting operation due to the elimination of modal frequencies in the operating frequency range of the saw blade. As can be seen from graph lines DES3-DES5, the other saw blades tested have several modal frequency values within the operating frequency range and therefore these blades suffer from significant vibration during cutting which results in poor cutting feel, poor surface finish and increased cut force. These results were end user tested and confirmed. It is noted that the samples DES4 and DES 5 are commercially available saw blades and each include multiple modal frequencies in the operating frequency range. Sample DES3 is an internally designed and tested blade design that is not publicly available.
FIG. 4 illustrates test data for a 61⁄2′′ blade having both 24 teeth and 40 teeth wherein the 24 tooth 61⁄2′′ blade has a operating frequency range of between 1,155 and 1,540 Hz and the 40 tooth 61⁄2′′ blade has an operating frequency range of between 1,925 and 2,566 Hz as illustrated in the graph of FIG. 4. The modal frequencies of the 24 tooth 61⁄2′′ blade are represented by the diamond shaped data points while the modal frequencies for the 40 tooth 61⁄2′′ blade are represented by the square data points in the graph of FIG. 4. Each of the 24 tooth and 40 tooth saw blades has the body slot design as illustrated in FIG. 1. On review of the data in FIG. 4, it can be seen that both the 24 tooth and 40 tooth saw blade designs include no modal frequencies in the respective operating frequency range for the saw blade.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

## Claims

1. A circular saw blade, comprising:
a circular metal disc including a central aperture and a plurality of teeth spaced around a periphery of said circular metal disc, a first plurality of fully enclosed body slots each generally equally spaced from a center of said circular metal disc by a first distance and a second plurality of fully enclosed body slots each disposed directly radially outward from a respective one of said first plurality of body slots and said second plurality of slots being generally equally spaced from said center of said circular metal disc by a second distance that is greater than said first distance wherein at least one of the slots of the second plurality of body slots has a pair of arcuate end sections and an undulating intermediate section disposed between the arcuate end sections, wherein the second plurality of body slots are generally evenly spaced circumferentially about the center, and wherein the first plurality of body slots and the second plurality of body slots are configured to provide one or zero modal frequencies in an operating frequency range of the saw blade.

2. The circular saw blade according to claim 1, wherein said first and second plurality of slots each have a width of 2 mm or less.

3. The circular saw blade according to claim 1, wherein said second plurality of slots have a length to width ratio of between 30 and 70.

4. The circular saw blade according to claim 1, wherein said circular metal disc includes a plurality of open ended slots extending radially inward from said periphery of said circular metal disc.

5. The circular saw blade according to claim 1, wherein said circular metal disc has a diameter of 71⁄4 inches.

6. The circular saw blade according to claim 1, wherein said circular metal disc has a diameter of 61⁄2 inches.

7. The circular saw blade according to claim 1, wherein said circular metal disc has a diameter of 81⁄4 inches.

8. The circular saw blade according to claim 1, wherein said plurality of teeth include 24 teeth.

9. The circular saw blade according to claim 1, wherein said plurality of teeth include 40 teeth.

10. The circular saw blade according to claim 1, wherein said undulating intermediate section includes at least four undulations.

11. The circular saw blade according to claim 1, wherein said second plurality of fully enclosed body slots include a pair of distal ends having a circular shape and a diameter approximately twice a width of said body slots.

12. The circular saw blade according to claim 1, wherein said first plurality of fully enclosed body slots and said second plurality of fully enclosed body slots each have distal ends that terminate along a common radius with a corresponding one of the first and second plurality of fully enclosed body slots.

13. A circular saw blade, comprising:
a circular metal disc including a central aperture and a plurality of teeth spaced around a periphery of said circular metal disc, a plurality of fully enclosed body slots each having a pair of arcuate end sections and an undulating intermediate section with a portion extending at least partially in a radial direction and disposed between said arcuate end sections, wherein the plurality of body slots are generally evenly spaced circumferentially about the central aperture, and wherein the plurality of body slots are configured to provide one or zero modal frequencies in an operating frequency range of the saw blade.

14. The circular saw blade according to claim 13, wherein said plurality of slots each have a width of less than 2 mm.

15. The circular saw blade according to claim 13, wherein said plurality of body slots have a length to width ratio of between 30 and 70.

16. The circular saw blade according to claim 13, wherein said undulating intermediate section includes at least four undulations.

17. The circular saw blade according to claim 14 wherein said plurality of body slots have distal ends that have a circular shape having a diameter approximately twice a width of said body slots.

18. The circular saw blade according to claim 13, wherein said circular metal disc includes a plurality of open-ended slots extending radially inward from said periphery or said circular metal disc.

19. A circular saw blade, comprising:
a circular metal disc including a central aperture and a plurality of teeth spaced around a periphery of said circular metal disc, said circular metal disc including a plurality of body slots designed to provide one or zero modal frequencies in an operating frequency range of the saw blade.

20. The circular saw blade according to claim 1, wherein the undulating intermediate section has a portion extending at least partially in a radial direction.

21. The circular saw blade of claim 19, wherein the plurality of body slots are configured to provide zero modal frequencies in the operating frequency range of the saw blade.

22. The circular saw blade of claim 19, wherein the plurality of body slots comprises a first plurality of fully enclosed body slots each generally equally spaced radially from the central aperture by a first distance.

23. The circular saw blade of claim 22, wherein the plurality of body slots further comprises a second plurality of fully enclosed body slots each disposed radially outward from a respective one of the first plurality of body slots.

24. The circular saw blade of claim 23, wherein the second plurality of slots are each generally equally spaced radially from the central aperture by a second distance that is greater than said first distance.

25. The circular saw blade of claim 23, wherein at least one of the slots of the first plurality of body slots and the second plurality of body slots has a pair of arcuate end sections and an undulating intermediate section disposed between the arcuate end sections.

26. The circular saw blade of claim 23, wherein the first plurality of body slots and the second plurality of body slots are generally evenly spaced circumferentially about the central aperture.

27. The circular saw blade of claim 19, wherein at least one of the plurality of body slots has a pair of arcuate end sections and an undulating intermediate section disposed between the arcuate end sections.

28. The circular saw blade of claim 19 wherein the plurality of body slots are generally evenly spaced circumferentially about the central aperture of the circular metal disc.