US2145760A - Electric hammer - Google Patents

Description

Jan. 31, 1939. R. T, FETHERSTON I ELECTRIC HAMMER Filed July 24, 1936 wV///lllllllllllllrllrl INVENTOR W T m a. yam

ATTORNEY Patented Jan. 31, 1939 ELECTRIC HAMMER Robert T. Fetherston, Milwaukee, Wis., assignor toMilwaukee Electric Tool Corporation, Milwaukee, Wis., a. corporation of Wisconsin 7 Application July 24, 1936, Serial No. 92,309

This invention relates tof portable percussion 7 tools such as electric hammers.

be of the type requiring a commutator. The motor V In such tools the driving-motor must ordinarily runsat very high speeds in order to provide the necessary power with light weight, and at each blow of the hammer there is transmitted to the body of the tool and to the motor a severe jar or shock. This shock results even during normal operation, and at times is greatly increased when the ram overruns, for any of various reasons, and

' strikesthe end of thechamber in which itreciprocates. Any such'repeated jar or shock is seriously detrimental 'to the operation of the motor commutator, causing sparking and undue wear, together with the loss of power in heating, and various other objectionable results. Similarly the vibration and shock isdetrimental to va- :rious' other parts of the device including the switch." -It is very objectionable to the hand of theoperator who guides the tool. Also it tends to loosen all the bolts, screws or rivets etc. hold-' ing the various parts together. Moreover the revibrations of increasing amplitude;

i The invention consists in the construction shown, described, and claimed herein, and in such variations or modifications of the structure shown and described as may be equivalent to the structure of the claims.

Like reference characters apply to the same parts throughout the specification, and in the drawing:v

' Figure 1 is a perspective view partly in section of a portable electric hammer incorporating the invention.

Figure 2'is a longitudinal section of the same Y device.

Figure 3 is a modified hammer structure also incorporating the invention.

The machine as shown in Figs. 1 and 2 includes a plurality of housings generally denoted by the numerals I and 2. The housing I is provided with a hand grip portion 3 in which is housed a switch 4 havinga trigger-like operatingfmember 5. Cables 6, I lead from the switch to a motor,

carried by housing I, generally denoted by the 4 Claims. (01. 125-33) numeral 8, which is of high speed, series wound type having a rotor 9 and a commutator I0 for supplying current to the rotor, there being commutator brushes such as II retained in the usual or any suitable manner in brush holders such as I2, to be spring pressed against the commutator.

Housing I also carries reduction gearing including the pinion I3 carried by an extension of the motor shaft and a gear I4 fixed on a shaft I5.

End plates I6, ll of housing I carry the bearings for pinion I3 and shaft I5, and are removably fixed with the main casting I8 in part by the means of screws such as I9 and in part by the bolts 20, 2I which extend through suitable flanges at the adjacent ends of housings I and 2 to fasten the housings together, there being another bolt 22 which does not extend through.

The housing 2 carries a shaft 23 coaxially alignediwith the shaft I5 and coupled to be driven from shaft I5 by a member 24. At its other end the shaft 23 carries a cam element 25 against which a cam member 26 is continuously pressed by a spring 21, the spring seating at the one end on an abutment member 28 fixed with housing 2, s and seating against the cam member 26 at its other end.

- Cam member 26 is fixed with a reciprocating hammer member 29. At the end of the housing I is fixed a tool receiving socket or member 30 providing a bore 3| through which the shank of a tool such as 32 may extend to be struck by the reciprocating member 29.

During revolution of shaft 23 from the motor 8 through the mechanism described the cam element 25, revolving against a cam face 33 of the cam member 25, presses the member 25 and the reciprocating member 29 to the right of Fig. 2 against the resistance of spring 21. The cam member 26 is of a form such that after traveling to the right the reciprocating member 29 is suddenly released to be thrust to the left in Fig. 2 by the spring, thereby delivering a hanmier blow against the end of the tool retained in the socket or bore 3I. At times, and particularly if there is not suflicient resistance to the tool the member 29 may overrun to strike the interior face of the member 30. The speed of the motor and the driving connections to the shaft 21' are such as to deliver a great many of such blows per minute at substantially equal intervals.

The shock and vibration incidental to the release of the member 26, and to the striking of the member 29 against the end of the tool or against member 30 are, unless'prevented, transmitted to the housings I and 2 and to each of the various elements of the device. Unless prevented, such vibrations cause sparking between the brushes II and commutator II] of the motor 8 and the various other objectionable results previously mentioned, particularly if the vibrations tend to be amplified or built up by the timed repetition of the hammer strokes.

To reduce the shock of individual blows and to prevent the building up of the amplitude of the vibration caused by repeated blows, there is pro-,

vided the following structure. A member or gasket 35 of suitable shock absorbing and vibration damping material such for instance as rubber is interposed between the adjacent end faces of the housings I, 2, the bolts 20, 2|, 22 passing through the gasket. In addition, underneath the heads of each of the bolts 25, 2 I, 22 there are additional gasket or washers of the shock absorbing or resilient material, such as 35, 31, 38. The bolts 20, 2 I, 22 are seated solidly against the end plate I! of housing I, whereby to effect a predetermined space underneath the bolt heads of such value as to provide a predetermined initial compression of the shock absorbing material of the several gaskets. By the means of the described construction each of the housings I, 2 is cushioned on shock absorbing and vibration damping material in either direction of its movemen't, set up by the hammer operation, relative to the other housing and each of the housings and every part carried thereby is effectively cushioned against individual blows and the structure is such as to provide efiect-ive damping against building up of vibration effects by repeated blows. Inorder to provide added surface bearing against the washers 35, 31, 38 the bolts 20, 2|, 22 are each provided with washers or bearing plates such motor and to provide for the brushes and commutator substantially the same life as would be obtained in a tool which was not subjected to the shock of the hammer blows, and to greatly increasing the 'e-fiiciency and power of the motor, and to greatly reduce the tendency of the motor and its commutator to overheat. There is also a material reduction in the shock and vibration transmitted to the hand of the operator, and substantially no tendency for the switch and various 'fastenings' to be loosened or damaged.

It is to be understood that the gaskets, as here shown may be made of various materials, and in some instances some or all of the gaskets may be replaced with springs of suitable form and position.

The hammer shown in Fig. 3 includes a motor, not shown, having commutators as indicated at '4'! and housed within a casing 42, there being a pinion '43 fixed on the motor shaft and engaging a gear 44 having fixed thereon an eccentric 45 which reciprocates a crank 45. Fixed with crank '46 is a rod 4'! which reciprocates a plunger or hammer member 48, guided in a housing 49, the member 48 being cushioned in either direction by springs 50, 5I. Carried at the lower end of member 48 is an anvil or hammer 52 positioned'to strike the end of a tool-53 at each reciprocation of crank 46, the tool being removably retained in a member 53a.

At the joint between the member 530, and housing 49 there is provided a resilient gasket,

and resilient washers 55, 56 associated with the bolts 51, 58 in a manner and for a purpose and result similar to the resilient gasket 35 and washers 36, 31 of the hammer shown in Figs. 1, 2.

The motor housing 42 and housing 49 are removably fixed together at a joint indicated at 54, and it is also contemplated that such joint may, if desired, be provided with resilient gaskets and washers (not shown) such as those shown for joining the motor and hammer housings I, 2 of Fig. 1, and for joining the member 530, and housing 49 of Fig. 3.

With the structure disclosed any shock which tends to move one of the housings I, 2 relative to the other primarily further compresses one of the opposed resilient devices consisting respectively of the gasket 31 and of the collective gaskets 36, 31,38. The other resilient device is simultaneously relieved of some of its initial compression set up by the bolts 25, 2I, 22. This cushions the shock and, in addition, a considerable portion of the force of the blow is absorbed or damped out by the deformation of the resilient devices and, in part by movement of one or both of the housings I, -2. Such rebound as occurs from 'a shock in the one direction is similarly cushioned and clamped by the corresponding but opposite action of the resilient devices in the other direction, and the result of the. combined damping of both the initial and rebound shocks is tosubstantially completely cushion and damp out any individual shocks irrespective of the rate at which they maybe repeated, and toentirely prevent any building up or amplification thereof which might otherwise occur for shocks repeated at regular intervals.

What is claimed is:

-1. In a portable percussion tool, the combination of a reciprocatory percussion element, a motor connected for operation of said element, a housing for said hammer element, a housing for said motor adjacent said element housing, said housings having adjacent faces along a plane transverse to the path of reciprocation of said element, a shock absorbing and vibration damping gasket interposed between said housings, bolts extending through said gasket for removably fixing said housings together, and another shock absorbing and vibration damping gasket associated with some of said bolts, both of said gaskets being simultaneously compressed by the tightening of said bolts to fix the one housing with the other.

2. In a percussion tool providing a hand-grip portion at the one end and a tool receiving socket at the other end, the combination of a-motor, a reciprocable hammer element adjacent said socket end and adapted to deliver percussion blows against a tool held in said socket, a transmission connecting said motor for reciprocation of said hammer element, a frame housing said hammer element and transmission and providing separable portions having faces adjacently arranged relative to a plane transverse to the path of reciprocation of said element, a shock absorbing and vibration damping member interposed between said faces, means fixing said housing portions together and simultaneously compressing said member toreceive thrust of one of said housing portions in one direction, and another shock absorbing and vibration damping member compressed by said means and positioned to receive the thrust of the last mentioned housing-portion in the other direction.

'3. In a percussion tool the combination of a housing, said housing including portions having adjacent faces along a plane transverse to the path of reciprocation of said element and between said hand grip and the exposed portion of said element, a shock absorbing and vibration damping gasket interposed between said adjacent faces for; compression by forces tending to reduce the spacing of said faces, and another shock absorbing and vibration damping gasket adapted for I compression by forces tending to increase the spacing of said faces.

housing providing a hand grip at the one end 4. In a percussion tool the combination of a there0f,- a reciprocable percussion element having a portion exposed at the other end of said housing, said housing including portions having adjacent faces along a plane transverse to the path of reciprocation of said element and between said hand grip and the exposed portion of said element, a bolt continuously urging the one of said housing portions in the direction of the other, and shock absorbing and vibration damping gasket means including a gasket portion interposed between said faces for compression by forces tending to reduce the spacing of said faces and another gasket portion associated with said bolt for compression by forces tending to increase the spacing of said faces, each of said gasket portions being simultaneously compressed by said bolt.

ROBERT T. FETHERSTON.

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