GB2100651A

GB2100651A - Hammer drill

Info

Publication number: GB2100651A
Application number: GB08214011A
Authority: GB
Inventors: Gerhard Rumpp; Manfred Spieth; Dieter Scholz
Original assignee: Hilti AG
Current assignee: Hilti AG
Priority date: 1981-06-29
Filing date: 1982-05-13
Publication date: 1983-01-06
Also published as: JPS584373A; FR2508370B1; DE3125453A1; NL8202047A; SE8203716L; FR2508370A1; CH655272A5; GB2100651B; YU130782A

Abstract

A hammer drill comprising a housing 1 and a tool holder 10 which is axially displaceable relative to the housing 1. During rotary drilling the tool holder 10 is supported in the axial direction against the housing 1. During percussion drilling radial play exists between the tool holder 10 and a percussion hammer 7 guided in the housing 1 as well as between the percussion hammer 7 and the housing 1. To cancel this play and provide for rotary drilling the tool holder 10 has, at its rearward end, a centering adjoint-piece 11a which when engaged with a centering bore 1e makes possible a direct centering of the tool holder 10 on the housing 1. <IMAGE>

Description

SPECIFICATION Hammer drill This invention relates to a hammer drill comprising a housing and a tool holder which is displaceable relative to the housing and which during rotary drilling is supported in the drill's axial direction against the housing.

Hammer drills of low and medium power (or performance) are in most cases intended not only for percussion drilling but also for rotary drilling. The criteria decisive for opti m.um working of such hammer drills are, however, different in the case of these two kinds of operation.

Whereas, in the case of percussion drilling above all the drilling capacity and thus a loss free transmission of the impact energy to the tool is decisive, in the case of rotary drilling, for point-exact application, for example, it is a matter essentially of the true running of the drilling tool. In order, during impact drilling, to prevent losses of the impact energy through parts that additionally have to be accelerated, it is customary for the percussion hammer to have axial play relative to the tool holder. Moreover, the percussion hammer carrying the tool holder is axially movable relative to the housing. This axial mobility of the percussion hammer relative to the housing and of the tool holder relative to the percussion hammer require, however, also radial play of these parts with one another. As a result of this radial play, in the course of time the aforesaid parts wear.Radial play is therefore increased and on the one hand the percussion hammer can assume an inclined position relative to the housing and on the other hand the tool holder can assume an inclined position relative to the percussion hammer.

The resulting angular displacement may extend as far as the drill tip and may amount to several millimetres. Thus, with the known hammer drills, accurate working during rotary drilling is difficult.

The problem underlying the invention is, therefore, to provide a hammer drill with which it is possible to achieve optimum working both upon the percussion drilling and upon the rotary drilling.

In accordance with the present invention, this problem is solved in that the tool holder and the housing have centering means which engage one in another upon axial supporting of the tool holder against the housing.

Since the tool holder is supported in the drill's axial direction against the housing only upon the rotary drilling, the centering means engage one another only during the rotary drilling. Thus, during percussion drilling, no wear of the centering means can occur. As a result of the direct centering of the tool holder on the housing, radial play between the housing and the percussion hammer is compensated for at the same time as radialy play between the percussion hammer and the tool holder.

For constructional reasons it is advantageous for the centering means to be respectively a centering adjoint-piece which is arranged on the tool holder, and a housing-side centering bore. Such a construction needs no special expenditure, since the housing has anyway a passage or through bore for the percussion hammer and thus it is merely necessary to provide on the tool holder a centering adjointpiece which is co-ordinated with the diameter thereof.

Both the centering adjoint-piece and the centering bore may be cylindrical. It is advantageous for the centering adjoint-piece and the centering bore to be tapered conically contrary to the drill's drilling direction since wear between the adjoint-piece and the centering bore may result in increased radial play.

Such a construction acts as a self-centering cone seat. In this respect, upon the squeezing of the hammer drill's trigger radial play is automatically cancelled.

As a result of the supporting of the tool holder against the housing there arises during the rotary drilling, a relative movement between the tool holder and the housing. In order, in this respect, to prevent as far as possible the occurrence of wear, preferably the centering means are sliding bearings. This may be effected, for example, in that the selected combination of material of the two parts sliding on one another has a small coefficient of friction. Suitable for this purpose are, for example, grey cast iron, bronze or certain plastics or synthetic materials, such as PTFE (Teflon) (Registered Trade Mark). The friction may, however, be reduced by lubricants such as grease or oil.

During rotary drilling, considerable axial forces may occur. In order to keep the friction losses as a result of these axial forces as low as possible, advantageously the centering means are roller bearings. For example, cone roller bearings which are able to absorb both axial and radial forces may be used as roller bearings.

So that the tool holder is supported against the housing in any position of the hammer drill, it is advantageous to provide for clamping means which brace the tool holder against the housing during the rotary drilling. Possible existing axial play is cancelled by the clamping means.

For the switch over from percussion drilling to rotary drilling and 'vice versa', it is advantageous for the clamping means to be in the form of a cam and incline, lifting flank or cam runner. The lifting flank may, for example, also be a coarse thread course. To facilitate actuation, spring elements may additionally be provided.

The invention will be described further, by way of example, with reference to the accompanying drawings in which: Figure 1 is a part sectional elevation of a preferred embodiment of the hammer drill of the invention, illustrated in the "percussion drilling" position; and Figure 2 is a view similar to Fig. 1, but illustrating the hammer drill in the "rotary drilling" position.

The preferred hammer drill illustrated in Figs. 1 and 2 comprising a housing which is designated as a whole by reference numeral 1 The housing 1 comprises a guide tube 1 a and an adjusting sleeve 1 b which is axially displaceable relative to the guide tube 1 a. To lock the adjusting sleeve 1 b to the guide tube 1 a in any specific position, a cam 1 C is provided on the guide tube 1 a and a lifting flank, incline or cam runner 1 d is provided on the adjusting sleeve 1 b. The adjusting sleeve 1 b and the guide tube 1 a are mutually braced by a spring 2. Arranged in the guide tube 1 a is a bearing 3. The bearing 3 serves to support a sliding bush 4. The bearing 3 is secured by a guard ring 5 in the guide tube 1 a and protected by a sealing ring 6 against the penetration of contaminations.Guided axially in the sliding bush 4 is a percussion hammer which is designated as a whole by 7.

For axial displaceability, the percussion hammer 7 has radial play relative to the sliding bush 4. Entrainment elements 8 mounted in channels 4a of the sliding bush 4 and depression 7a of the percussion hammer 7 serve to transfer torque to the percussion hammer 7 and to limit the axial displaceability of the percussion hammer 7 relative to the sliding bush 4. In its rearward region the sliding bush 4 is connected to a cylinder 9.

Arranged at the front end of the percussion hammer 7 is a tool holder 1 0. The tool holder 10 has a reception sleeve 11 which is connected by securing elements 1 2 to the percussion hammer 7. The securing elements 1 2 are held radially by a retaining ring 1 4. The reception sleeve 11 contains, furthermore, locking elements 1 3. The rearward end of the reception sleeve 11 is a centering adjointpiece or projection 11 a. The centering adjointpiece 11 a is, in its rearward region, tapered conically contrary to the drill's drilling direction. Arranged on the adjusting sleeve 1 b of the housing 1 is a centering bore 1 e which corresponds to the centering adjoint-piece 11 a.In its central region the reception sleeve 11 is surrounded by an axially-displaceable grip sleeve 1 5. Upon pushing-back of the grip sleeve 1 5 against the force of a compression spring 1 6, the locking elements 1 3 can be disengaged radialiy. An end piece 1 7 is bolted to the reception sleeve 11. A tool 20 is inserted with its rearward plug-in end 20a into the tool holder 1 0. In so doing, the locking elements 1 3 engage depressions 20b on the plug-in end 20a of the tool 20.

In the "percussion drilling" position shown in Fig. 1, the percussion hammer 7 together with the tool holder 10 connected thereto is limitedly displaceable relative to the housing 1. As a result of the radial play of the percussion hammer 7 relative to the sliding bush 4, as well as by any radial play possible existing between the percussion hammer 7 and the reception sleeve 11, the tool 20 may be radial displaced relative to the drill's drill ing axis. However, in the case of percussion drilling this does not act further in a disturbing manner.

In the "rotary drilling" position shown in Fig. 2, the adjusting sleeve 1 b is unlocked from the guide tube 1 a and shifted by the spring 2 against the tool holder 10. In so doing, the centering adjoint-piece 11 a passes into engagement with the centering bore 1 e.

The tool holder 10 is thus centered directly on the housing 1. By means of the spring 2 the tool holder 10 is axially braced against the housing 1. The cam 1 C and the lifting flank 1 d are in this respect again in engagement and prevent any shifting back of the adjusting sleeve 1 b upon the squeezing of the tool. To reduce friction, the centering bore 1 e may be a sliding or roller bearing. Instead of the spring 2, axial bracing of the tool holder 10 against the housing 1 may also be effected by an appropriate design of the lifting flank 1 d.

Claims

1. A hammer drill comprising a housing and a tool holder which is axially displaceable relative to the housing and which during rotary drilling is supported in the drill's axial direction against the housing, characterised in that the tool holder and the housing have centering means which engage one in another upon axial supporting of the tool holder against the housing.

2. A hammer drill as claimed in claim 1, characterised in that the centering means are respectively a centering adjoint-piece which is arranged on the tool holder and a housingside centering bore.

3. A hammer drill as claimed in claim 2, characterised in that the centering adjointpiece and the centering bore are tapered conically contrary to the drill's drilling direction.

4. A hammer drill as claimed in claim 1, 2 or 3, characterised in that the centering means are sliding bearings.

5. A hammer drill as claimed in claim 1, 2 or 3, characterised in that the centering means are roller bearings.

6. A hammer drill as claimed in any preceding claim, characterised in the provision of clamping means which brace the tool holder against the housing during rotary drilling.

7. A hammer drill as claimed in claim 6, characterised in that the clamping means are a cam and a lifting flank incline or can runner.

8. A hammer drill substantially as herein before described with reference to and as illustrated in the accompanying drawings.