Cutting – Tool or tool with support – Toothed blade or tooth therefor
Reexamination Certificate
1999-08-06
2001-10-09
Bray, W. Donald (Department: 3725)
Cutting
Tool or tool with support
Toothed blade or tooth therefor
C076S112000, C076S027000, C083S835000
Reexamination Certificate
active
06298762
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to circular saws, having fine-pitch uniformly shaped non-metallic teeth, for cutting thin materials.
Background: Cutting Tool Hardness
Since the beginning of the Bronze Age, toolmakers have sought to improve the durability and functionality of tools by modifying their cutting edges. Early processes included work-hardening of bronze, and adding steel edges to iron implements. That process continues to this day as new, super-hard materials are developed and new applications are found for older ones. In general, the ideal cutting tool surface should combine abrasion-resistance (hardness) with shock-resistance (toughness). (Of course there are many other relevant properties, including yield strength, rigidity, temperature limits, corrosion resistance in some applications, etc.)
Solutions evolved as described in the Neibl U.S. Pat. No. 907,167(1909) and the Blum U.S. Pat. No. 1,535,096(1926), where a band of very hard steel was welded to another supporting band of softer steel and teeth were cut into the hard steel band. Whitaker, U.S. Pat. No. 1,130,649, (1916) and the Napier U.S. Pat. No. 1,352,140(1921), approach the same problem by applying special heat treatment and tempering to the cutting edge.
U.S. Pat. No. 1,919,358 to Bem suggested applying Stellite to the edge of a saw body, and then grinding teeth into that material. In the Bern patent, a hard facing material (in the form of a welding rod) was applied to the edge of a saw blade body by melting with an acetylene torch. Although Stellite is now an obsolete material, “hardfacing” materials are often applied by torch or spraying to the wear-edges of plows, bulldozer blades and rock drill stems. It is tempting to assume that these techniques could be used to build up a useful hard layer on a lathe tool or a saw blade, as proposed in the Bem patent. Unfortunately, such coatings suffer from high porosity, very low strength, and poor impact properties, rendering them unfit as cutting tools.
Following the development of tungsten carbide materials produced by powdered metal technology by Schroeter, U.S. Pat. No. 1,594,615 (1925), tungsten carbide moved steadily into tooling applications.
Background: Carbide-Toothed Circular Saws
Cutting tools (especially woodworking tools) often use inserted teeth of a material which is harder than the hardest of steels. The most common material used for this is a “cemented carbide,” which typically includes small grains of tungsten carbide bonded into a matrix with a metal (typically cobalt). (Because the strength and hardness of the matrix are derived from the grains of tungsten carbide, such cemented carbides are often referred to simply as “carbide.”) Such “carbide” saw tips have a hardness of about 92(Rockwell A).
FIG. 3
shows a typical configuration of a section of a carbide tipped circular saw. Typically the main part of the saw blade
310
is a steel plate, and the carbide teeth
320
are brazed onto the leading edge of tooth profiles
330
which are cut out from the steel plate.
Some firms manufacture only the steel bodies of circular saws, which are hardened, tempered and finished in every way except for tipping, and are then sold to other saw manufactures who specialize in carbide tipping. Other firms manufacture the complete saws including both the steel bodies and the installed tips. In either case, the same standard carbide tips are used in the fabrication of the blades. The steel bodies are normally made of high-carbon alloy tool steel, then a pocket is ground into the periphery of the saw body to accommodate the carbide tips. The tips may be ¼ to ⅜ inches long, 0.062 to 0.093 inches thick and from 0.10 to 0.375 inches wide, depending on the width of the finished saw blade.
The normal industry practice is to affix the carbide tips to the steel bodies by means of brazing, typically with silver bearing brazing material. While satisfactory for most applications, the brazed joints limit the operating temperature and loads (particularly lateral loads) under which the blade can operate.
Additionally, the thickness of the carbide and the size of the brazed area provided by the seat pocket have a large bearing on the integrity of the joint. However, the same factors that favor a strong brazed joint also limit the number of carbide inserts that can be placed along the cutting edge of the saw. This, in turn, ultimately limits the minimum spacing between adjacent teeth, the number of teeth on the saw, and the number of teeth per inch of periphery. For example, carbide-tipped ten-inch blades are currently available with up to 100 teeth, but no more. This implies that the pitch of a conventional carbide-tipped saw cannot be less than one centimeter.
In the woodworking industry, carbide tipped saws are typically 8 to 20 inches in diameter. Depending on their function, the 8 inch blades may have between 24 and 48 teeth, and the larger saws 60 to 100 teeth. For cutting non-ferrous metals, the number of teeth is typically between 24 and 80 for saws ranging from 8 to 18 inches in diameter. However, saws with greater tooth density (i.e. more teeth per inch) would be required to produce superior finishes and to cut thin materials.
The geometry of brazed carbide circular saw construction limits tooth density to a maximum of about 10 teeth per inch of saw diameter, i.e., 100 teeth for a 10 inch saw. Some applications require a higher tooth density than carbide tipped saws can provide. In woodworking, these applications include the cutting of plywood and veneers where fine finish is required and splintering is unacceptable. Tooth density of at least twice that available from carbide tipped saws is required to cut thin metals, including thin wall tubing and extruded shapes. In addition, fine tooth saws leave less burr on cut surfaces.
More recently, the same technology has been applied to use polycrystalline diamond inserts which are dimensionally similar to and applied in the same manner (by brazing) as carbide. However, the same limitations on tooth pitch will still apply.
When faced with a problem requiring more saw teeth than carbide tipping can provide, the manufacturer has two choices. He can choose a steel saw and forego the benefit of the longer lifetime of carbide (which is about 4:1 over high speed steel), or he can select a solid carbide saw. The steel saws are relatively inexpensive but dull rapidly. Solid carbide saws have superior wear properties, but are brittle and are not available in sizes greater than 6 inches in diameter. Moreover, solid carbide saws are very expensive, typically 15 times that of a steel saw, as shown in
FIG. 4
, where the comparative costs of a steel blade versus a solid carbide blade are plotted at various diameters.
Background: Grit-Surfaced (Non-Toothed) “Saws”
A common type of cutting tool is a circular blade which does not have shaped teeth at its edge, but which is simply coated with a diamond grit. Such cutting tools are commonly referred to as diamond “saws,” but in fact they do not perform the same type of material-removal action as is performed by a saw with shaped teeth. A saw with shaped teeth, when it is operating correctly, will carve off chips of material. By contrast, a grit-coated blade will have more of a scraping or abrasive action. (See generally Jim Effner, Chisels on a wheel (1992 ); and Peter Koch, Utilization of Hardwoods Growing on Southern Pine Sites (1985 ); both of which are hereby incorporated by reference.) A cutting action is greatly preferable for many applications, to produce a cleaner cut, lower temperature, and lower power requirements.
Background: Cutting Thin Materials
Sawing action is smoothest when there is always at least one tooth in the cut. For cutting very thin materials, this requires a very fine tooth pitch. If the tooth pitch cannot be made as small as the material thickness, it should still be made as small as possible.
For example, for cutting aluminum extrusions with ten-inch blades, blades with up to 300 teeth are often used; howev
LaRue John D.
Turfitt Ron
Bray W. Donald
Formby Betty
Groover Robert
Groover & Associates
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