US3108644A - Power hammer - Google Patents

Description

Oct. 29, 1963 H. c. GUSTAFSON 3,108,644

POWER HAMMER Filed May \16. 1960 5 I 23 mmvrox IFIIG. 3. HJALMER C,GUSTAFSON ATTORNEY United States Patent ()fiice v awash Patented Oct. 29, 1963 3,108,644 PGW'ER HAMMER Hjalmer Q. Gustafson, Denver, (Zola; Hazel A. Gustaison, heir to Hjahner (I. Gustatson, deceased Filed May 16, 1960, Ser. No. 29,339 1 (llaim. (til. $73-$18) This invention relates to high-energy impact tools, and more particularly to portable tools utilizing a high speed rotary shaft for actuating a short-stroke, high rate of impact power tool for breaking, chipping, drilling operations, etc.

Portable, power-driven impact tools, frequently called power hammers, have been proposed in many forms. In recent years electric motors have been the main power source for such portable hammers, but essentially all have been based on a theory of operation of using a heavy impact member with a relatively slow rate of impact of the weighted member on an operating tool. Further, such electrical tools transmit the rotary action of an electric motor shaft into a reciprocal motion of the weight member by means of rotary cams with dropping followers operated directly from the motor shaft. In such tools there is a high degree of wear and a short operating life of the parts, particularly due to the friction between the cam and the cam follower and the impact produced between these same parts.

Under dusting and gritty conditions of drilling and chiseling the Wear is greatly accentuated. Such tools are, further, subject to destructive vibration unless the impact of the hammer is directed against a tool which is in operative position against a working face. In other words, operating the hammer free from a work face will actually produce destructive vibrations which can destroy the power hammer in a relatively short time.

According to the invention, I have provided a highenergy, low-vibration housing, power hammer which uses a very low-throw eccentric cross head on a high speed shaft to drive an impact member at a short-stroke, very high frequency rate. The low-throw cross head provides a high speed reciprocal motion of a Weighted member, through an indirect connection, in the form of a relatively stillhelical spring between the cross head and the hammer member. This arrangement reduces the number of parts, the weight and the impact forces on the parts. The spring connector greatly reduces vibrations being transmitted to the mechanism housing. There is, also, provided an impact member mounted in a series of shaped bores in an arrangement forming an air cushion against which the energy of the hammer member may be expended in the absence of an operating tool.

Included among the objects and advantages of the present invention is a high-energy, low-vibration power hamrner of very lightweight for breaking, chipping, drilling and similar operations. The tool is provided with a relatively stiff spring connecting member between a lowthrow, high-speed cross head and a hammer member arranged to strike an operating tool at a high frequency so that the energy of the impact is directed onto the tool and is essentially not transmitted to the tool housing. The device, furthermore, provides a power hammer of substantially reduced number of parts to thereby reduce wear of the parts and maintenance of the tool. The device includes an impact member which with passages in the housing provides an air cushioning for the striking hammer of the device to thereby prevent free cycling of the hammer member, and to prevent transmission of destructive vibrations to the tool housing when running without an operating tool.

These and other objects and advantages of the invention may be readily ascertained by referring to the description and appended drawings in which:

FIG. 1 is a side elevational view, in partial section, of an impact tool according to the invention arranged in operating position against a tool;

FIG. 2 is another side elevation of the device of FIG. 1 taken along section line 2- .2;

FIG. 3 is a detailed view of an operating position of a cross head of the device;

FIG. 4 is an enlarged detailed view of the impact member in operable arrangement with a tool according to the invention;

FIG. 5 is a detailed view of the impact member of the device shown in operative position without an operating tool;

FIG. 6 is a cross section of a tool retainer taken along section line 6-6 of FIG. 2 showing a tool retaining position; and

FIG. 7 is a cross section similar to the cross section of FIG. 6 with the tool retainer in tool removal position.

The description of the device is set forth in relation to a flexible shaft operated device, however, it is obvious that a direct connected electric motor could be mounted on the device in the same relation as to its housing as the flexible shaft. It is, therefore, to be understood that the description is intended for illustration only and not to limit the spirit or the scope of the invention to the precise details set forth in the following description.

In the device illustrated in PKG. 1, the high-energy power hammer includes a lower housing l threadedly engaged to an upper housing 2. A pin 3 connects the two housing members together insuring positive retention of the parts under the vibration forces of the impact device. The pin 3 is mounted on a circular retaining spring 4 which is mounted in rabbets 5 and 6 on housings 2 and 1 respectively forming a groove in position to hold the spring and thus retain the pin 3. The housing 2 is provided with a manipulating handle 7 at one end and a tool bore 8 at the opposite end. A shaft housing 12 is secured to the upper housing 2 by means of bolts 14, and a shaft 15 is journaled for rotation therein. The inner end of the shaft 15 includes an eccentric shaft 16, which is only slightly offset from the axis of the shaft 15. The outer end of the shaft 15' includes a rectangular bore 17 into which a rectangular drive member 18 may be inserted for driving the shaft. The rectangular drive member 13 is mounted on the end of a rotary flexible shaft 19' which is retained in position on the housing 12 by means of a screw cap 20. The opposite end of the flexible cable 19 is, obviously, mounted and rotated by an electrical motor, which is not shown, and for safety a cover or sheath 21 is provided over the flexible shaft 19.

A cross head 25 is mounted on the eccentric member 16 by means of a bearing set 26, FIG. 2, so that the cocentric shaft 16 freely rotates in the cross head 25 which is maintained essentially non-rotary. A boss 27 is integrally mounted on the cross head 25 and extends toward the tool bore 8. A relatively stiff helical spring 28 is securely mounted on the boss 27 by means of a tight frictional fit or in some instances by threading the spring on threads on the exterior of the boss 27.

The housing member 1 is provided with a bore 39, in which is mounted a reciprocal impact or hammer member 31. The impact member is arranged for free reciprocal movement within the bore. A-boss 34 integrally mounted on the impact member 31 is securely mounted in the spring 28 in a manner similar to the spring connection with the cross head. The lower end of the bore 30, toward the tool bore, is provided with a short, smaller diameter bore portion 33. The end opposite the boss 34 on the impact member 31 is provided with an integrally or securely attached extension 37 which is arranged with essentially close fit in bore 33, but is reciprocable therein. As the impact member 31 operates in the bore 30, the parts should be maintained well lubricated, and the extension 37 is, likewise, lubricated for movement in the short bore portion 33. The lubrication, also, provides for the maintenance of the air cushion, as explained below.

Since the device is a portable power hammer, it is convenient to provide a switch for the electric motor, which rotates the flexible shaft 19, at the hammer itself, and for this purpose an on and off switch member 45} is provided on the handle 7. This switch member connects and disconnects the leads of an electric cable 41 which is interconnected with the electric motor power leads. In the event the flexible shafit is replaced by a direct connected electric motor, the power line 41 would normally be connected to the motor attached to the housing.

A drill, chisel or other type of tool is arranged for insertion into the tool bore 8 according to conventional means. In this instance, a drill steel is provided with a shaft 56*, an impact ring 51 and a square shank 52, which is arranged for mounting in the square bore 8. The shank portion includes a notch 55 into which a retaining member or pin 53 falls for temporarily locking the tool in the tool bore. A cylindrical spring 54 retains the pin 53 in the notch 55 for holding the tool. It is to be noted that the notch 55 is sufiiciently long to permit reciprocal movement of the drill steel in the tool bore. Further, the end of the shank is bevelled to aid insertion of the shank past the pin.

As illustrated in FIG. 6, the drill steel shank 52 is mounted in the square tool bore 8 with the member 53 mounted in the groove 55. The member 53 is held by circular spring 54 holding the drill steel in the hammer. In FIG. 7 the drill steel is either being removed or inserted and the member 53 is riding on an edge of the shank in upper position out of the notch 55'.

In one very convenient size a quarter pound impact member, which is member 31 with attached boss 37, is oscillated by a shaft 19 rotating at at least about 7200 r.p.m. or higher. In this instance, the offset or eccentric shaft 16 is oifset of an inch 50 that there is a sixteenth inch throw at and 180 of the cross head which in turn oscillates the hammer at about /s of an inch. As shown in FIG. 3, the eccentric is in a 90 position illustrating that the angular deflection is only about 4, which is easily accommodated by the bending of the spring. At the high speed at which the hammer operates, the energy of the impact on the tool is sufficient to effectively drill, chip, chisel or otherwise utilize the impact energy. At this high speed and low throw there is essentially no vibration, especially due to the spring connection between the cross head and the hammer. The spring provides a flexible connection which permits the lateral movement of the cross head and the reciprocal movement of the impact member.

When the drill steel, or other tool, is in place and the hammer is pressed against it by the operator bearing down on the handle, operation of the hammer imparts the energy of the high frequency impacts to the work face, that is, any surface being acted on by the tool. So long as the operator bears against the tool, the shank contacts the impact member on its stroke away from the cross head.

In the event that the tool is operated without the drill steel pressed against a work face, or if no tool is attached to the hammer, the movement of the impact member tends to cause it to over run its normal reciprocal movement. This over running causes boss 37 to enter bore 33 trapping air in the annular space between bore 30 and the boss 37. This air is compressed damping the movement of the impact member, and absorbing the energy of the movement. This prevents undue vibrations and prevents transfer of the full force of the impact to the housing. As the cross [head pulls the impact memher back for another impact movement, the dead air pocket is opened and heated air (due to the compression) escapes, thus preventing over heating of the tool. Thus the combination of the spring connector and the air cushion provides means for transmitting impact forces to an operating tool, but cushions such impact forces in the absence of such tools.

Light weight, portable power hammers may be effectively made using the weights and speeds outlined above, and where desirable, the speed may be increased or the size and weight of the parts may be changed. Maintenance is obviously simple since there are few moving parts and no complicated moving structural parts.

Having thus described my invention, what is desired to be secured by United States Letters Patent is:

A power hammer of the class described comprising a housing having a manipulative handle at one end and a tool holding passage at the opposite end, a main bore in said housing communicating with said tool holding passage, said tool holding passage being of substantially smaller dimensions than said bore, a relatively light weighted hammer member reciproca'oly mounted in said main bore, a cylindrical extension secured to said hammer in tool striking position, said main bore including a stepped down bore adjacent said tool holding passage for reciprocably accommodating said extension, there being a shoulder between said step-down bore and said main bore, a low-throw eccentric shaft mounted in said main bore, a cross head mounted on said shaft adjacent to and spaced from said hammer member, a relatively stiif spring secured to and interconnecting said cross head and said hammer member, means for rotating said shaft at a high speed of at least about 7200 r.p.m., and said extension arranged to move cyclically from a position out of said stepped down bore into said stepped down bore for trapping air between said cylindrical extension and said main bore on over-travel of said hammer member to cushion the impact of said hammer member in absence of an operating tool.

References Cited in the file of this patent UNITED STATES PATENTS 1,625,211 Jones Apr. 19, 1927 2,240,598 Wilke May 6, 1941 2,613,662 Reynolds Oct. 14, 1952 FOREIGN PATENTS 718,582 Great Britain Nov. 17, 1954

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