The present application relates to cutting tools used to break up hard surfaces and to the tips incorporated in such tools,
Hard surfaces such as concrete, asphalt and stone are broken up using machines having a rotating member, such as a wheel or a drum, and a plurality of tools located on the outer surface of the rotating member. When the rotating member is forced against the surface to be excavated, the cutting ends of the tools successively impact against the surface and break off small portions of the material, thereby advancing the cut.
The tools for such machines have a generally tapered cutting end behind which is a coaxially mounted cylindrical shank sized to rotatably fit within the cylindrical bore of a tool holder. The forward end of the cutting end of the tool body has a seat into which the base of a tungsten carbide cutting insert is brazed.
The hard surfaces against which the tools are forced cause the tool bodies and the inserts therein to become rapidly worn and it is common to replace all of the tools of a cutting machine after a single day""s use. The machine may carry one hundred and fifty tools or more and it may wear out several thousand tools during a single construction season. Replacement tools, therefore, are made in standard sizes which fit into machines made by several manufacturers. The seat at the forward end of the standard tool body has an inner diameter of approximately 0.710 inches and the tungsten carbide insert brazed into the seat has a base diameter of approximately 0.690 inches. The diameter of the inner wall of the seat was chosen to provide and adequate surface area for the braze to retain the insert in the seat.
The most expensive portion of the cutting tool is the cost of the tungsten carbide insert. It has been found that an insert having a conical forward cutting tip and a frustoconical mid section which widens to the full diameter of the base (about 0.690 inches) is not the most economical configuration to manufacture and use because machines fitted with such tips do not operate at their best efficiency. The problem is that such tips have too great of an outer diameter and require a great amount of horsepower to force the tip against a hard surface. Also, when such machines are used during the hot summer months, the steel tool bodies which retain over sized tungsten carbide inserts become worn and fail long before the inserts.
To reduce the cost of such tools and improve their efficiency, it has been common to provide a tip with a contoured profile in which the forward cutting end diverges outwardly to a maximum useable diameter which is substantially less than that of the diameter of the seat. The tip disclosed in Ojanen, B1 U.S. Pat. No. 4,497,520 depicts such a configuration. Contoured tips such as disclosed by Ojanen, nonetheless employ an excess amount of tungsten carbide to fill the seats into which the inserts are mounted. It would, therefore, be desirable to provide an improved tip having the benefits of the contoured profile but would employ less tungsten carbide and therefor be less expensive to manufacture.
Briefly, the present invention is embodied in an improved cutting tool having a tool body with a cutting portion and a cylindrical mounting portion sized to fit within the bore of a tool holder on a machine. The cutting end of the tool body has a seat with a general cylindrical wall into which the hardened tungsten carbide insert is brazed.
In accordance with the invention, the tungsten carbide insert has a tip portion, a base portion and a frustoconical mid portion extending from the tip portion to the base portion. The base portion defines a diameter substantially less than the given diameter of the cylindrical wall of a seat. The base further has a plurality of radially extending projections, the outer ends of which define a cylinder having a diameter which is a little less than the diameter of the seat such that the radial projections around the circumference of the base will center the base of the insert within the seat prior to brazing.