GB2344562A

GB2344562A - A hand machine tool

Info

Publication number: GB2344562A
Application number: GB9922564A
Authority: GB
Inventors: Manfred Koching
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1998-09-30
Filing date: 1999-09-23
Publication date: 2000-06-14
Anticipated expiration: 2019-09-23
Also published as: GB9922564D0; NL1013171C2; DE19844806B4; DE19844806A1; NL1013171A1; GB2344562B

Abstract

A hand machine tool, e.g. a cord saw 10, comprises a motor housing 12, which accommodates a motor with a motor shaft 18, and a gearing housing 14, which accommodates an angle gearing 20, 32. The angle gearing 20, 32 comprises a small bevel-gear pinion 20, which is rotationally rigidly arranged on the motor shaft 18, engaging with a ring gear 32, which is centrally penetrated by an output shaft 26. The output shaft 26 is rotatably mounted in the gearing housing 14 and at its end emerging from the gearing housing 14 supports a tool 16. The output shaft 26 is rotatably mounted relative to the ring gear 32, the ring gear 32 being coupled by means of an eccentric device 38, 40, 44 with a thrust element 42 linearly guided in the gearing housing 14. Rotation of the ring gear 32 is convertible into a reciprocating movement of the thrust element 42, the thrust element 42 being coupled with the output shaft 26 in such a manner that the reciprocating thrust element rotates the output shaft 26 and therefore the tool 16 in a reciprocating movement or a rotary-pivoting movement. As well as being a cord saw, the hand machine tool may also be a brush or grinding sleeve.

Description

2344562 A hand machine tool, more particularly a cord saw State of the art

The invention relates to a hand machine tool according to the generic type of claim I.

A dental hand tool is known from DE-PS 573 143 which comprises an abrasivecoated belt, which is driven so as to reciprocate and is to be looped around the tooth which is to be ground on its outer surface and machines said tooth in a reciprocating manner. This machine has a complex construction and is expensiv e to manufacture.

In addition, a stationary cord saw is known from US-A 5 239 978, which has a complex, heavy drive and whose construction is unsuitable for use as a hand machine tool.

Advantages of the invention In contrast, the hand machine tool according to the invention having the characterising features of claim I offers the advantages of a simple, compact construction of the gearing for a reciprocating drive of the saw wire with a long stroke, which as a result of a reliable discharge of sawdust and its minimal regular dwell time in the tool engagement position ensures a high saw advance.

As a result of the compact construction, the hand machine tool according to the invention only requires a relatively small number of components and a low mass, so that it is particularly easy to handle.

2 The compact construction results from the fact that the output shaft is rotatably mounted relative to the ring gear, the ring gear is coupled by means of an eccentric device with a thrust element linearly guided in the gearing housing, the rotation of the ring gear can be converted into a reciprocating movement of the thrust element and the thrust element is coupled with the output shaft in such a manner that the reciprocating thrust element rotates the output shaft and therefore the workpiece in reciprocating fashion.

As a result of the fact that the eccentric device is formed by an annular groove arranged eccentrically on one of the ring surfaces of the ring gear, a cam of the thrust element engaging in said annular groove, the ring gear exhibits particularly quiet running and is well balanced.

As a result of the fact that the cam of the thrust element supports a roller bearing and engages with said bearing in the annular groove and is supported therein, a particularly low-ftiction force transmission between the ring gear and the thrust element is possible.

As a result of the fact that the thrust element is coupled with the output shaft via a friction or tooth engagement, the reciprocating movement of the thrust element can be transformed particularly easily into a rotary-pivoting movement or reciprocating rotary movement of the output spindle.

As a result of the fact that, in addition to the first thrust element, a second thrust element is coupled to the output shaft opposite the first thrust element and in the opposite direction of movement, an expedient weight balance is attained in the interior of the gearing housing and in relation to the output shaft.

3 As a result of the fact that the ring gear is arranged axially secured relative to the output shaft and is rotatably mounted via a needle bearing, a simple and lowftiction arrangement of the ring gear is ensured.

As a result of the fact that the thrust element supports a toothing and the output shaft supports a matching counter toothing, a high degree of efficiency of the force transmission between the thrust element and the output shaft is ensured.

As a result of the fact that the tool is constructed as a cord roller, to which the ends of the saw wire can be releasably secured, e.g. by means of a screw, and upon which the saw wire at least partially rolls, a particularly secure movement transmission of the rotary-pivoting movement to the saw wire, whose length can be freely selected, is ensured.

As a result of the fact that the saw wire is prevented from slipping off the cord roller by a bracket, which can be pushed onto the cord roller, particularly safe operation is possible.

As a result of the fact that the cord roller can be replaced by another tool, for example a brush or a grinder, the cord saw can also be used as a roller grinder or as a brush.

As a result of the fact that the hand machine tool supports a support arm, which can be displaceably supported with its free end against a workpiece, safe sawing with saw wire is possible, since the saw wire can be held in a tightly tensioned manner and consequently the danger of injury to the operator, for example as a result of the oscillation of loose saw wire regions (so-called whipping), is reliably avoided.

4 Drawings An embodiment of the invention will be explained in further detail in the following description with the aid of the associated drawings, in which:

Figure 1 is a partial longitudinal section through the hand machine tool according to the invention, Figure 2 is a plan view of the ring gear of the hand machine tool and Figure 3 is a section through the cord roller according to the numerals III-III in Fig. 1.

Description of the embodiment

The cord saw 10 illustrated in Figure I comprises a motor housing 12, onto which a gearing housing 14 is flanged, from which a tool support constructed as a cord roller 16 emerges at the bottom. The motor housing 12 supports an electromotor, not shown, whose motor shaft 18 projects into the gearing housing 14 and at its free end non-rotatably supports a small bevel-gear pinion 20.

On its outer circumference, the motor housing 12 supports a button 22 of an electrical on/off switch, not shown, for the electromotor, an electric cable 24 emerging from the rear end of the motor housing 12 to supply energy to said electromotor.

The gearing housing 14 comprises an output shaft 26, which is rotatably mounted in the gearing housing 14 perpendicular to the motor shaft 18. In the upper region of the gearing housing 14, a roller bearing 28 supports the upper end of the output shaft 26 and on the opposite side in the lower region of the gearing housing 14 a second roller bearing 30 supports the lower end of the output shaft 26, which emerges with its free end from the bottom of the gearing housing 14 and nonrotatably accommodates a cord roller 16 with a saw wire 56 looped around the cord roller to form a loop 57. Pressed onto the outside of the cord roller 16 is a bracket 60, which prevents the saw wire 56 from slipping off the cord roller 16. The saw wire 56 is detachably secured with its two ends 55 (Fig. 3) to the cord roller 16 by means of screws 62.

A ring gear 32 meshing with the small bevel-gear pinion 20 is centrally penetrated by the output shaft 26 and is rotatably mounted relative to said shaft via a needle bearing 34 and is secured in this position with a slight clearance by means of axial securing means, not described in further detail.

On the rear side 36 of the toothing side, the ring gear 32 supports an eccentric annular groove 38, in which a cam 40, which is fixedly connected to an elongate thrust element 42, engages with slight clearance. On its free end, the cam 40 supports a needle bearing 44 and in this manner is mounted in the annular groove 38 of the ring gear 32 with particularly low friction.

The rack-like thrust element 42 is secured against rotation in linear guides 46, 48 of the gearing housing 14, is mounted so as to reciprocate easily and on its flat side facing the output shaft 26 supports a flat toothing 50. A matching, round counter toothing 52 of the output shaft 26 engages in this flat toothing 50.

The output shaft 26 and the thrust element 42 are held against one another in a clearance-free manner or with a slight degree of pretension by means of a suitable 6 degree of tolerance of the linear guides or by further means, not shown, so that the toothing 50 of the thrust element 42 always remains reliably in engagement with the counter toothing 52 of the output shaft 26.

When the motor, not shown, and therefore the motor shaft 18 with the bevel-gear pinion 20 is set in rotation, the ring gear 32 also rotates with a correspondingly reduced rotational speed and thereby reciprocates the cam 40 with the thrust element 42 to the right and to the left in the plane of the drawing in the direction of the movement arrow 54, the stroke of the thrust element 42 corresponding to the eccentricity of the annular groove 38. In this respect, as a result of the tooth engagement the thrust element 42 drives the rack 26 to produce a reciprocating rotational movement or. rotary-pivoting movement.

The larger the eccentricity of the annular groove 38 relative to the centre of the ring gear 32, the larger the stroke of the thrust element 42 and the greater the number of rotations of the output shaft 26 in each direction of rotation.

Together with the output shaft 26, the cord roller 16 also rotates in reciprocating fashion, driving the saw wire 56, which is looped around the cord roller 16, forms a loop and is freely selectable in its length, by pulling the saw wire 56 at alternate loop ends.

The saw wire 56 is provided in known manner with abrasive particles or teeth and its ends secured in the cord roller are secured relative to the cord roller by screws. During its operation, the saw wire 56 wraps in the manner of a loop around the workpiece, acting in the manner of a chain saw.

Schematically indicated, a support arm 58 is displaceably secured to the housing 7 and is somewhat longer than half the length or than the maximum loop length of the saw wire 56 which can be practically realised and can slide forwards by this length beyond the output shaft 26. In this manner, the cord saw 10 can be supported during sawing relative to a workpiece, not shown, e.g. a branch or a tree, so that the saw wire 56 is sufficiently tensioned at all times and secured against whipping movements. In this manner, the danger of injury to the operator by the saw wire regions fitted with abrasive particles or blades is considerably reduced. Whipping can result from the saw wire being tensioned or held too loosely relative to a workpiece, the machine oscillating to and for relative to the workpiece as a result of the expanded saw wire and in turn reinforcing the expansion of the saw wire.

Figure 2 shows the rear side of the ring gear 32, the eccentric annular groove 28 and the cam 40 engaged therein being recognisable. In addition, the output shaft 26 as well as the motor shaft 18 and the bevel-gear pinion 20 are at least partially recognisable.

It is clear from this drawing that the thrust element 42 indicated in Figure 1 has been deflected forwards and backwards by a linear stroke which is equal to the eccentricity of the annular groove 3 8 relative to the centre of the output shaft 2 8.

Figure 3 shows the cord roller 16 as a detail in cross section, the saw wire 56 which is laid around the cord roller and secured thereto being visible.

In an embodiment of the invention which is not illustrated, a further thrust element is mounted on the opposite side of the first thrust element so as to be linearly displaceable parallel to said first thrust element and is coupled via its own flat toothing with the round toothing of the output shaft, and is either mounted so as 8 to reciprocate without coupling with the ring gear and is merely used for balance, or also engages with its own cam in a further annular groove of the ring gear and can improve the movement transmission from the ring gear to the output shaft. In addition, the cord roller supports a bracket, which is pushed onto the outside of the cord roller, is driven by the cord roller and during sawing prevents the saw wire from sliding axially outwards off the cord roller.

In a further embodiment of the invention which is not illustrated, both thrust elements are elastically pretensioned relative to the output shaft by spring means.

In another embodiment of the invention which is not illustrated, the annular groove is constructed as a separate part which is displaceable relative to the ring gear, so that the stroke of the thrust element is variable by the displacement of the annular groove relative to the ring gear.

9

Claims

1. A hand machine tool, more particularly a cord saw (10), with a motor housing (12) and a gearing housing (14) for accommodating, respectively, a motor with a motor shaft (18) and an angle gearing (20, 32), which is formed by a bevel-gear pinion (20), which engages with a ring gear (32) and is rotationally rigidly arranged on the motor shaft (18), the ring gear (32) being centrally penetrated by an output shaft (26), which is rotatably mounted in the region of its shaft ends in the gearing housing (14)) and at its end emerging from the gearing housing (14) supports a tool (16), characterised in that the ring gear (32) is rotatably mounted relative to the output shaft (26), more particularly supported by a central roller bearing, and is coupled with a thrust element (42) linearly guided in the gearing housing (14), more particularly with an eccentric device (3 8, 40, 44) mounted on the ring gear (3 2), by means of which the rotation of the ring gear (32) can be converted into a, more particularly, linear reciprocation of thrust element (42), the thrust element (42) being coupled in a positive or non-positive locking manner with the output shaft (26) and driving the output shaft (26) and therefore the tool (16) to produce a rotary oscillation.

2. A hand machine tool according to claim 1, characterised in that the eccentric device comprises an annular groove (38), which is eccentrically arranged on one of the end faces of the ring gear (32) and in which a cam (40) of the thrust element (42) engages.

3. A hand machine tool according to claim 2, characterised in that the cam (40) of the thrust element (42) supports a roller bearing (44), more particularly a needle bearing, and is supported via said bearing in the annular groove (38).

4. A hand machine tool according to one of the preceding claims, characterised in that the thrust element (42) is coupled with the output shaft (26) via a friction or tooth engagement.

5. A hand machine tool according to claim 4, characterised in that the thrust element (42) is provided on its circumference with a flat toothing (50) in the manner of a rack, and the output shaft (26) supports a counter toothing (52) fitting into the toothing (50) of the thrust element (42).

6. A hand machine tool according to claim 1, characterised in that the ring gear (32) is axially fixed relative to the output shaft (26), more particularly is rotatably mounted via a needle bearing (34).

7. A hand machine tool according to claim 1, characterised in that the tool (16) is constructed as a cord roller, to which the ends of a saw wire (56), which can be looped around a workpiece, are secured and upon whose circumference the saw wire (56) rolls.

8. A hand machine tool according to claim 1, characterised in that the cord roller (16) can be replaced by another tool, for example a brush or a grinding sleeve.

9. A hand machine tool according to claim 7 or 8, characterised in that a support arm (58) is displaceably arranged on the housing (12, 14), the free end of said support arm being supportable against a workpiece, and the support arm (5 8), measured from the centre of the tool (16), is approximately I I half the length of the saw wire (56).

10. A hand machine tool according to claim 9, characterised in that the support arm (58) can be elastically pretensioned relative to a workpiece.

11. A hand machine tool substantially as herein described with reference to the accompanying drawings.