US 2161062 A
Description (OCR text may contain errors)
June 6, 1939. R. J. KILLGORE 2,161,062
PERCUSSION TOOL Filed March 24, 1954 [/v m TOR A 7'7'ORNEY.
Rosa/QT (1 K/LLGORE Patented June 6, 1935.
UNITED STATES ATEN OFFICE 3 Claims.
My invention relates to a tool of percussion type adapted to be driven against or into the material on which the tool is caused to operate.
My invention is of especial utility in the break- 5 ing up of materials, such asconcrete, brickwork, rock, etc. The razing of concrete structures and the breaking up of concrete pavements for the purpose of cutting ditches or removing or replacing a road surface is generally accomplished by use of a sharp pointed steel bit or gad operated in an air hammer. Due to the very abrasive character of the materials operated upon, it is found that tools used for this purpose lose their cutting points very quickly and must be frequently resharpened. My invention provides a tool adapted for the very severe service of breaking up concrete andother materials of a similar character, which tool is self-sharpening. In addition to being self-sharpening, this tool is otherwise as strong and durable as the steel, gads now employed.
It is an object of the invention to provide a percussion tool of the above character comprising abar or body of tough metal which will stand up for a maximum period of time against the severe crystallization influences encountered in air hammer operation, having an insert of extremely hard steel set into the pointed cutting end thereof in such a manner that the insert, whichd'ue to its 30 great hardness is somewhat brittle, will not break in ordinary usageof the tool but will preserve a sharp point for the tool owing to the fact that the surrounding metal in which the insert is held, although being of larger volume, wears faster 35 than the point of the insert and thereby preserves a continuously sharp cutting point for the tool.
It is an object of theinvention to provide a simple manner and means for holding the hard insert in the softer tough bar in such a manner that the insert will not break up due to the stresses applied thereto.
A further object of the inventionis to provide in a tool of the above character a tough metal body of characteristic form surrounding the in- 45 sert so as to firmly secure the insert in such a manner that forces received by the point of the insert are transmitted from the side walls of the insert to the supporting body of metal instead of through the end of the insert to the supporting 50 body of metal, thereby producing a distribution of forces which will prevent breakage of the insert due to its severe use.
Further objects and advantages of the invenus ing part of the specification.
Referring to the drawing, which is for illustrative purposes only,
Fig. 1 is a view showing a preferred form of my invention and a manner of its use. I
Fig. 2 is a perspective view of the percussion 5 tool.
Fig. 3 is an enlarged sectional view of the point of the tool.
Fig. 4 is a view looking at' the pointed end of the tool. 10
In Fig 1 I show my percussion tool or gad fitted into an air hammer |2 so that it may be manipulated by a workman l3 against a body of material M, such, for example, as concrete, which is to be broken up so that it may be removed. it
' 'fect. The forward end of the bar l5 has a longitudinal opening 2| leading inwardly therefrom, this opening being tapered inwardly as shown and receiving therein a hard metal insert 22, the end of which is sharpened or pointed; as shown at 23, to cooperate with the end of the bar in forming the cutting point of the percussion tool.
The opening 2| is made of greater length than the insert 22, and the insert 22 is tapered to correspond to the taper of the opening 2| so that the insert 22 will not bottom in the opening or hole 2| but leaves a space 24 between the inner end 25 thereof and the bottom 26 of the opening 2| which is rounded so that no sharp corners exist from which a crack may readily start in the metal forming the bar I5. v
In the preferred form of my invention the re- 40 action forces exerted against the tip or point. 23 of the insert 22 are transmitted through the tapered side wall thereof to the tapered wall of the opening 2| instead of directly axially through the insert 22 to the bottom of the opening 2|. In
this construction the forces are distributed through a comparatively large external area of the insert 22, with the result that the very severe impact which must be transmitted through the insert 22 does not result in the insert being broken, even though it may be of relatively brittle material.
The bar l5 is-made from a metal which has toughness as its outstanding characteristic. It is found that gads are subject to breakage in the 5 shank portion thereof due to crystallization of the metal; therefore, the metal employed must be extremely tough. I find that satisfactory results can be obtained where the bar I5 is made from chrome-tungsten steel or similar alloys, including molybdenum and other of the efiective hardening elements. The insert 22 is made of a metal having extreme hardness as its principal characteristic. Accordingly, such metal is quite brittle and could not be employed throughout the entire percussion tool or gad due to its brittleness. In my invention, however, the hard insert 22 is supported, and the stresses are distributed therein, in'such a manner that breakage thereof does not ordinarily occur. I find that one metal suitable for use in the insert 22 is high speed tool steel, of which there are several kinds, such as Panther, Rex, etc. In order to provide a control of the wear at the cutting end of the tool I5, the hardness of the bar [5 and the hardness of the insert 22 are proportioned with this end in view. I find that good results are obtainable where the bar It: has a hardness of 40 Rockwell and the insert 22 has a hardness of 60 Rockwell. It is evident, however, that these values may be materially changed in the practice of the invention.
The taper of the insert 22 and the opening 2! is such that the insert 22 will not be forced into the opening in the use of the tool. The degree of taper accordingly is determined from the characteristics of the metals employed in the bar It: and in the insert 22. For example, as the strength of the metal surrounding the opening 2i increases, the taper of the opening may be decreased, but should the bar l5 be made of a metal which, although very durable, is of decreased tensile strength, the taper of the opening 2| and of theinsert 22 will be proportionately increased. A simple manner of placing the insert 22 in operative position consists in heating the walls of the bar 35 surrounding the openingZI so as to increase the diameter of the opening and then force the insert 22 into the opening while it is thus enlarged, the metal walls surrounding the opening 2i shrinking down upon and firmly gripping the insert 22 when they are returned to normal temperature. 1
An additional feature of the invention resides in the formation of a point on the end of the bar l5 which will be of such form that ample metal will be provided for support of the hard metal insert. Accordingly, the wall or walls 20 of the point l8 extend through a relatively small angle of taper 21 to a plane A--A near the extreme end of the tool, whereupon the taper is abruptly increased throughout the short area 28 in the formation of the actual point of the tool. In this manner the metal at 30 is maintained amply thick for the support of the insert 22.
Although I have herein shown and described my invention in simple and practical form, it is recognized that certain parts or elements thereof are representative of other parts, elements, or mechanisms which may be used in substantially the same manner to accomplish substantially the same results; therefore, it is to be understood that the invention is not to be limited to the details disclosed herein but is to be accorded the full scope of the following claims.
I claim as my invention:
1. A cutting tool of the character described for use in cutting hard materials, comprising: a body of relatively tough metal having a tapered opening extending inwardly from the cutting portion thereof, the inner end of the wall forming said opening being gradually reduced to form a bottom for said opening without the formation of an abrupt shoulder; and a tapered insert of hard metal in said opening in such position that the inner end of said insert will be spaced from the bottom of said opening, the walls of said body around said opening being so formed as to hold said insert in radial compression.
2. A cutting tool of the character described for use in cutting hard materials, comprising: a body of relatively tough metal having an opening extending inwardly from the cutting portion thereof, the inner end of the Wall forming said opening being gradually reduced to form a bottom for said opening without the formation of an abrupt shoulder; and an insert of hard metal in said opening in such position that the inner end of said insert will be spaced from the bottom of said opening, the wallsof said body around said opening being so formed as to hold said insert in radial compression with sufficient force to substantially prevent shattering of said insert.
' 3. A digging tool having a tapered metallic point and being formed with a longitudinally extending tapered bore disposed centrally thereof with its outer larger diameter agreeing substantially with the diameter of the outer end of the body portion, a tapered steel insert of greater hardness than that of the body portion, the largest diameter of said insert substantially agreeing with the diameter of the end of the point, the body portion of the insertfitting into the tapered bore and being of a length substantially less than the length of the bore and having an outer point projecting beyond the end of the pointed body portion.
ROBERT J. KILLGORE.