EP2529887A2 - Grinding tool with an eccentric shaft in a grinding spindle - Google Patents

Abstract

The grinding unit has a grinding spindle (10) that is arranged on the eccentric shaft (50), and a grinding structure (170) for holding the grinding wheel (140). A rolling bearing is supported on free end of eccentric shaft through grinding disc housing, in opposite to rotation direction of spindle. The eccentric shaft is equipped with balancing portions. A freewheel is arranged between eccentric shaft and grinding spindle.

Description

The invention relates to a grinding unit with an eccentric shaft arranged in a grinding spindle for supporting a sanding disc bearing an abrasive.

From the DE 196 08 969 A1 an electric hand grinder is known in which in an enclosure, an electric motor via an eccentric shaft occupied with an abrasive grinding disc placed in an oscillating oscillatory motion. For this purpose, the sanding pad is suspended on the housing so that it is mounted to oscillate transversely to the eccentric shaft. The center of the grinding plate is supported by means of a rolling bearing on the eccentric pin.

The present invention is based on the problem to develop a einwechselbares grinding unit, which has a simple and robust construction with a small space.

The problem is solved with the features of claim 1. For this purpose, the balanced eccentric shaft is mounted in a torsionally rigid and longitudinally displaceable manner on or in the grinding spindle. On the free end of the eccentric shaft of the - in at least one direction of rotation relative to the grinding spindle freely movable - sanding pad is mounted directly or by means of a sanding disk housing over at least one rolling, sliding or air bearings.

With the invention, an abrasive aggregate is provided which i.a. suitable for processing large-area wood or wood substitute surfaces. The sanding pad of the grinding aggregate contributes thereto e.g. exchangeable grinding wheels, polishing wheels or corresponding brushes.

The grinding unit adapted to the supporting machine tool via a known tool interface carries its sanding pad on a spring-mounted eccentric shaft. The sanding pad is in this case freely rotatably mounted on the eccentric shaft, so that the abrasive moves with respect to the eccentric shaft driving aggregate-own grinding spindle on a circular path with no or almost no self-rotation. Depending on the unit type, the diameter of the circular path is 2 to 25 mm. Of course, the circular path of the tool center point is distorted in a transverse movement of the grinding spindle in a regular trajectory.

The tool is pressed by arranged in the grinding unit spring elements against the workpiece surface to be machined. For example, the spring elements, such as disc springs, which are combined into stacks or packages. Instead of the disc springs and coil springs can be used. Does the grinding unit a compressed air connection, for example supplied with compressed air via the tool interface, a resilient contact pressure can also be effected via a pneumatic spring. In a simple construction, the weight of the eccentric shaft and the grinding plate can be sufficient to achieve the necessary contact pressure.

Figur 1:

Perspektivische Ansicht eines Schleifaggregats;

Figur 2:

Längsschnitt zu Figur 1;

Figur 3:

Variante zu Figur 2;

Figur 4:

Perspektivische Ansicht eines Mitnahmezapfens mit drei Passfedern;

Figur 5:

Perspektivische Ansicht einer Exzenterwelle;

Figur 6:

vergrößerter Teilschnitt eines Freilaufes nach Figur 3;

Figur 7:

Perspektivische Unteransicht eines Schleiftellers, verkleinert;

Figur 8:

Perspektivische Draufsicht auf den Schleifmittelträger nach Figur 7;

Figur 9:

Perspektivische Unteransicht eines Schleifmittelträgers, verkleinert.

Further details of the invention will become apparent from the dependent claims and the following descriptions of schematically illustrated embodiments.

FIG. 1:

Perspective view of a grinding aggregate;

FIG. 2:

Longitudinal section too FIG. 1 ;

FIG. 3:

Variant too FIG. 2 ;

FIG. 4:

Perspective view of a driving pin with three feather keys;

FIG. 5:

Perspective view of an eccentric shaft;

FIG. 6:

enlarged partial section of a freewheel after FIG. 3 ;

FIG. 7:

Perspective bottom view of a sanding plate, reduced;

FIG. 8:

Perspective top view of the abrasive carrier after FIG. 7 ;

FIG. 9:

Perspective bottom view of an abrasive carrier, reduced in size.

The FIGS. 1 and 2 show as a tool unit a einwechselbares grinding unit, which can also be referred to as a grinding head. To FIG. 2 is the grinding unit in the embodiment from a hollow grinding spindle (10), in which an eccentric shaft (50), for example, by a stroke of 6.5 mm is mounted longitudinally displaceable and torsionally rigid. At the lower end of the eccentric part of the eccentric shaft (50), a sanding pad housing (100) sits on whose threaded pin (113) a sanding pad (140) is arranged together with an abrasive carrier (160) and a grinding wheel (170).

The hollow grinding spindle (10) consists essentially of a tool interface and a tubular guide section (15). It has, for example, a total length of 111 mm, with about 46% of the length attributable to the tool interface. The tool interface here is a hollow shank taper (11) with face abutment (HSK) according to DIN 69893. Alternatively Morse taper according to DIN 228, ISO steep taper according to DIN 2080 or DIN 69871, Capto ^® interfaces or the like can be used.

The guide section (15) has a radial outer wall (23) which at the end remote from the hollow shank taper (11) has a e.g. 12 mm wide, precision machined sealing seat area (24). The latter has an outer diameter of about 53 mm.

The guide section (15) has on the inside a cylindrical bearing bore (16) with a flat bottom (17). The finely machined bearing bore (16) has an inner diameter of 38 mm. In the bottom (17), for example, four threaded holes (18) are arranged, the center lines lie on the mantle of an abstract cylinder whose center line coincides with the center line (29) of the grinding spindle (10). The center line (29) is at the same time the center line of the short shaft taper (11).

In the center of the bottom (17) there is a Zylindenkbohrung (13), which connects the adapter cavity (12) of the hollow shaft short taper (11) with the bearing bore (16). The small diameter of the cylinder counterbore (13) has e.g. a 5 mm diameter.

In the region of the free end, the bearing bore (16) has an inner ring groove (19) for receiving a securing ring (47).

On the bottom (17) of the bearing bore (16) by means of four countersunk screws (45) has a driving pin (30) attached. The one-piece driving pin (30), see. FIG. 4 , consists of a flange (31), a pin (33) with three longitudinal grooves (42) and a spring guide tube (36). The flange (31) has four through holes (32) with 90 ° counterbores. The centrally formed on the flange (31) pin (33), for example, at a length of 31 mm has a diameter of 18 mm, has as longitudinal grooves, for example, three circumferentially equidistantly distributed keyways (42), in each case a corresponding, made of plastic produced key (43) is pressed with a tight fit. At the pin (33), a spring guide tube (36) connects, which has a length of 14 mm, for example, at a diameter of 7.1 mm. The spring guide tube (36) carries at its free end a 1.5 * 15 ° bevel. Between the pin (33) and the spring guide tube (36) is a flat collar, which is aligned normal to the center line (29).

The driving pin (30) has a two-stage through hole (41), the first - located in the region of the flange (31) - quarter is a cylinder counterbore.

In the guide section (15) of the grinding spindle (10) sits in a ball cage (46), the eccentric shaft (50). The ball cage (46) has a length of 54 mm, for example. He stores here in 24 rows 264 balls, for example, have a diameter of 4 mm. The eccentric shaft (50), cf. also FIG. 5 , Is at the same time along the driving pin (30). It is like the grinding spindle (10) and the driving pin (30) made of the insert steel 16 MnCr5, consists of an externally machined bearing section (51), a mass balance section (53), a sealing seat portion (72), a bearing seat portion (74) and a Threaded section (75). The mass balancing section (53) adjoins the bearing section (51) via a ring-channel-like recess (57) which is, for example, 11 mm deep and concentric with the center line (29), cf. also Figures 2 and 3 , The inner diameter of the recess (57) measures, for example 53.5 mm, so that the sealing seat portion (24) of the radial outer wall (23) of the grinding spindle (10) fits with play. In the vicinity of the end face of the mass balance section (53) facing the bearing section (51), the radial inner wall of this section (53) has an inner ring groove (58) for receiving a sealing ring in the form of an O or quad ring (59).

The radial outer wall (23) of the mass balance section (53) has a center line (65) according to FIG. 2 offset by several millimeters, for example 3.55 mm, to the right eccentric. In the embodiment according to FIG. 3 is dispensed with an off-center outer wall. The local outer wall (56) is concentric with the center line (29) aligned. In order to be able to function as a mass balance section (54), it has, for example, a bow-shaped or crescent-shaped unbalance recess (63). The latter is on the side of the eccentric shaft (50), on which the center line (79) is located. To a generated by the imbalance recess (63) noisy To prevent whistling, the imbalance recess (63) by a lid, such as a clamping lid (64), be closed.

After the Figures 2 . 3 and 5 located below the mass balance portion (53, 54) of the sealing seat portion (72), the bearing seat portion (74) and the threaded portion (75). All three sections (72, 74, 75), which together are also referred to as the eccentric section (71), have a center line (79) offset eccentrically to the left by, for example, 3 mm with respect to the center line (29). The finely machined sealing seat portion (72) has a diameter of 32 mm, for example, at a width of 6 mm. The subsequent bearing seat portion (74), on which a deep groove ball bearing (122) is arranged, has a length of 12 mm and a diameter of 25 mm. Between the seal seat portion (72) and the bearing seat portion (74) a planar stop collar (73) is arranged. The eccentric shaft (50) terminates with the 7 mm threaded portion (75), eg an M25 * 1.5 thread, for receiving a shaft nut (123). Between the latter and the stop collar (73), the deep groove ball bearing (122) is axially clamped.

The eccentric shaft (50) has a multi-stepped through-hole (80), cf. FIG. 3 and 5 whose center line (89) is congruent to the center line (29). The first HSK-near zone is the 26 mm long dead zone (81), for example. The finely worked area-wise cylindrical inner wall of this zone (81) has, for example, only 0.1 mm smaller diameter than the outer diameter of the pin (33). In it, for example, three longitudinal grooves (82) are arranged, in which the feather keys (43) of the pin (33) - to form a shaft-hub connection - are guided in sliding seats.

Instead of the torque transmission by means of feather keys (43) can be between the pin (33) and the eccentric shaft (50), for example also a wedge and hub profile with internal centering 18 * 22 * 6 according to DIN 5471 or a serrated profile 17 * 20 according to DIN 5481-1 can be used.

As an open space for the finely machined inner wall of the entrainment zone (81) serves a spatially subordinate, e.g. At least 6.5 mm long puncture zone (83). Their length is greater than the stroke of the eccentric shaft (50) in the grinding spindle (10). The puncture zone (83) ends in a plan reason.

The next zone is the e.g. 43 mm spring return zone (84) whose diameter is e.g. 14.1 mm. It has a flat bottom that serves as the spring pad. The spring guide zone (84) is followed by a threaded zone (86). It is e.g. an M5 internal thread according to DIN 13-1.

To FIG. 3 the eccentric shaft (50) to the left of the internal thread (86) has a parallel to the center line (29) extending air guide bore (77) which intersects with a short cylindrical air guide zone (85). The between the spring guide zone (84) and the threaded zone (86) located air guide zone (85), for example, has a diameter of 12 mm.

On the bearing seat portion (74) of the eccentric shaft (50) sits one of the shaft nut (123) axially fixed deep groove ball bearing (122). The deep groove ball bearing (122) supports the sanding pad (140) by means of the substantially cylindrical sanding pad housing (100) made of an aluminum alloy. The latter consists of an upper and a lower part (101, 111). The top (101) is in the form of a sleeve with a central, single stepped bore (102). In the cylindrical wall of the narrower bore portion a lip seal (121) is pressed, the upwardly oriented Sealing lip on the sealing seat portion (72) of the eccentric shaft (50) rests. The cylindrical recess of the upper part (101) has, for example, an inner diameter of 47 mm. It serves to receive the outer ring of the deep groove ball bearing (122) and the centering collar (112) of the lower part (111). In the lower end face of the upper part (101), which measures an outer diameter of 60 mm, six equidistantly distributed threaded bores (103) are arranged. At the middle level of the cylindrical outer wall of the upper part (101) there are six radial transverse bores (104), cf. FIG. 1 , each having a depth of 5 mm. The transverse bores (104) are each offset by 30 degrees relative to the threaded bores (103).

The lid-shaped lower part (111) carries on its flat lower end face a threaded pin (113) with an M16 thread and six holes (114) with cylinder counterbores. In these holes (114) sit the cylinder screws (125), which hold the lower part (111) in the threaded holes (103) of the upper part (101) and axially fix the rolling bearing (122) via the centering collar (112). On the side facing the upper part (101), the lower part (111) has a short cylindrical recess (115) into which the shaft end of the eccentric shaft (50) projects with the shaft nut (123). The mounted sanding pad housing (100), without consideration of the threaded pin (113) has a height of e.g. 30 mm.

It is also possible to install the rolling bearing (122) or a corresponding plain bearing directly sealed in sanding plate (140).

To FIG. 3 is the sanding pad housing (100) over the variant of the FIGS. 1 and 2 about 12 mm longer. On the Seating seat portion (72) of the eccentric shaft (50) sits between the stop collar (73) and the rolling bearing (122) has a freewheel (130) whose inner ring (131) on the sealing seat portion (72) and its outer ring (132) in the inner bore (102 ) of the upper housing part (101) is pressed in each case rotationally fixed. In the exemplary embodiment, the freewheel (130) has 20 clamping bodies (133) which contact each other. In the contact region each clamping body (133) on both sides in the freewheeling direction of the outer ring (132) widening groove (134). In each of the grooves (134) on both sides sits a support ring (135). The outer curvature of the individual clamping body (133) is offset relative to the inner curvature in the clockwise direction so that the outer ring (132) stops when the inner ring (131) rotates counterclockwise. When the inner ring (131) rotates clockwise, the clamp bodies (133) rotate slightly counterclockwise, causing them to jam between the rings (131) and (132). As a result, the inner ring (131) with the outer ring (132) with.

Instead of the sprag freewheel (130), a clamping roller freewheel, a pawl freewheel or another comparable freewheel can also be used.

On the threaded pin (113) of the sanding pad housing (100), a sanding pad (140) is screwed. The sanding pad (140), cf. also FIGS. 1 and 7 , is a disc in the center, for example, 14 mm thick plastic or an aluminum alloy, which tapers between a diameter of 63 mm and its outer diameter of 115 mm with an angle of 20 degrees. It has a central internal thread (142), cf. FIG. 3 , over which it is screwed onto the threaded pin (113) of the sanding pad housing (100). To FIG. 3 the upper face of the sanding pad (140) has a 0.5 mm deep intake turn (169) with a diameter of 50 mm.

Around the center line (29), for example, eight continuous oblique holes (143), see. FIG. 7 arranged in a 45-degree angle graduation. They have a diameter of 10 mm. The center lines of the oblique holes (143) lie on an imaginary cone whose cone point, as seen in the direction of abrasive (170), about 90 mm in front of the abrasive carrier (160) facing end face (141) on the center line (29). The cone angle of the imaginary cone is 40 degrees.

Between the oblique holes (143) and the internal thread (142) is a 9 mm deep and 15 mm wide annular channel (145), whose largest diameter measures 52 mm. The annular channel (145) is incorporated from the lower end face (141) into the sanding pad (140).

The end face (141) has four more, but smaller, decentralized annular channels (146) lying on a circle whose diameter is 85 mm. Each of these annular channels (146), which lies at a pitch of 90 degrees between each two inclined holes (143), has a depth of 5 mm, a maximum diameter of 21 mm and a width of 6 mm. In the center of each annular channel (146) is an M4 threaded hole (147).

On the lower end face (141) of the sanding plate (140) is located on a substantially disc-shaped, elastic made of a plastic or rubber abrasive carrier (160), see. FIGS. 8 and 9 , Around the center line (29), for example, eight continuous longitudinal bores (164) are in a 45-degree angular pitch on a circle with a diameter of 65 mm arranged. They each have a diameter of 10 mm. If the abrasive carrier (160) for in the variant after FIG. 3 used, he also has a central bore (165).

In order to arrange these longitudinal bores (164) congruently in front of the lower openings of the oblique bores (143) of the sanding disc (140), the upper side (161) of the abrasive carrier (160) has four annular ribs (162) which are arranged in the decentralized annular channels (146) of the Sanding pad (140) fit. The inner flanks of the annular webs (162) come to rest against the inner flanks of the annular channels (146).

In the lower side (167) of the abrasive carrier (160), four fixing holes (163) provided with cylinder countersinks are arranged. The center lines of these bores (163) are aligned with the center lines of the ring webs (162) arranged on the upper side (161). In addition, the underside (167) of the abrasive carrier (160) is coated, for example, with a fabric having a plurality of small barbs like a hook and loop fastener.

In the assembled state, the abrasive carrier (160) rests with its upper side (161) on the end face (141) of the grinding disc (140), wherein the annular ribs (162) center in the decentralized annular channels (146). The S-abrasive carrier (160) is fastened with four Allen screws (168), cf. FIG. 1 , bolted to the sanding pad (140).

On the underside (167) of the abrasive carrier (160) is after the FIGS. 1 to 3 arranged as an abrasive or tool, for example, a circular, flexible grinding wheel (170). It has matching to the corresponding abrasive carrier (160) a plurality of holes corresponding to the local bores (164, 165). The abrasive backing (160) facing the abrasive backing carries a thin fleece having a plurality of woven, closed, small loops in which the barbs of the underside coating of the abrasive backing (160) interlock. In the front of the grinding wheel (170) facing the workpiece during the grinding process, a large number of abrasive grains of comparable grain size is incorporated.

To allow a pendulum movement of the sanding plate (140) in the range of several degrees, the sanding pad (140) of the variant according to the FIGS. 1 and 2 eg in a spherical roller bearing according to DIN 635, a self-aligning ball bearing according to DIN 630, a spherical roller bearing according to DIN 635, a comparable sliding bearing with spherical sliding surfaces or the like are stored. In this case, between the free end face of the threaded portion (75) of the eccentric shaft (50) and the bottom of the recess (115) of the housing lower part (111) a pressure piece can be centrally arranged, whose - due to the between the parts (50) and (100 ) existing relative movement wear-resistant - detent ball engages in a direction of the center line (79) normally aligned sanding pad (140) in a corresponding recess recess.

After replacing the equipped with a grinding wheel (170) grinding aggregate in the main spindle of the machine tool, such as a woodworking machine, this is rotated. As a speed, for example, 50 to 300 rpm initially provided. The mounted on the eccentric shaft (50) sanding plate (140) rotates after a short time with the speed of the eccentric shaft (50). Simultaneously with the startup, the grinding unit is moved to the workpiece surface to be machined as long moved in the normal direction until the grinding wheel (170) contacts them. Upon contact of the grinding wheel (170) with the workpiece surface, the sanding pad (140) is decelerated. At the same time, the grinding spindle (10) is delivered in the tenth millimeter to millimeter range normal to the workpiece surface, so that a defined pressure force results from the plate springs (127) arranged between the driving pin (30) and the eccentric shaft (50). During this infeed, the eccentric shaft (50) slides almost free of play over the ball cage (46) deeper into the bearing bore (16) of the grinding spindle (10).

In this delivery phase or at the end of this phase, the speed of the grinding spindle (10) is increased to a certain operating speed. The latter is depending on the application in the range of 1000 to 10,000 rpm.

If during the grinding process, the center line (29) of the grinding unit stationary to the workpiece surface, the center of the grinding wheel (170) describes a circular path with a radius corresponding to the eccentricity (76) of the eccentric portion (71) of the eccentric shaft (50). Since in this case the sanding pad (140) has no or almost no inherent rotation relative to the machine tool or relative to the stationary housing of the main spindle, the eccentric section (71) rotates in the sanding disk housing (100) at full or almost full operating speed.

Now, if the grinding unit is moved by the machine tool, for example, on a straight line extending parallel to the workpiece surface, the center of the grinding wheel describes a trajectory, for example, represents an oblique projection of a helix or one between two boundary lines progressive oscillating curve. The two boundary lines have a distance of twice the eccentricity.

Now, if the equipped with a freewheel (130) grinding head used, see. FIG. 3 For example, with a right-handed grinding spindle (10), it shows the behavior described above. However, if the grinding spindle (10) is reversed to a left turn, the freewheel (130) couples the sanding pad housing (100) to the eccentric shaft (50). Thus, the sanding pad (140) rotates synchronously with the grinding spindle (10). In a regular machining cycle, for example, the grinding spindle (10) is now operated 95 to 99.9% of the grinding time with operating speed in the clockwise direction, wherein the freewheel (130) has no clamping action. The remaining grinding time rotates the grinding spindle (10) in the counterclockwise direction - ie in the opposite direction - at a greatly reduced speed, eg 50 to 300 rpm. In this phase, the sanding pad (140) inevitably changes its angular position oriented around the center line (29) relative to the housing of the machine tool main spindle, whereby, inter alia, an undesired recurring abrasive structure is avoided on the workpiece surface.

It is also possible to use the slower counter-clockwise rotation with revolving rotating grinding wheel (170) as a highly abrasive roughing movement, while the clockwise rotation with its high speed and the unused freewheel is used for finishing.

The variant after FIG. 3 is additionally equipped with a compressed air supply. The compressed air is supplied to the machine side of the machine tool main spindle the adapter cavity (12) of the hollow shaft short-taper (11). From there, the compressed air passes through the cylinder counterbore (13) into the through hole (41) of the driving pin (30). Latter is connected via the transverse groove (35) and the longitudinal groove (34) with the spring guide zone (84). The compressed air flows there via the disc spring bores along the retaining screw (87) into the air guiding zone (85). The air guide zone (85) communicates with the bore (165) of the abrasive carrier (160) and the corresponding bore of the abrasive wheel (170) via the air guide bore (77) and the bore (117). The compressed air exiting centrally from the grinding wheel (170) flows radially along the workpiece surface in order, for example, to reach the rear side of the grinding plate (140) via the bores (164) and (143), from where it is suctioned off on the machine side.

LIST OF REFERENCE NUMBERS

10

grinding spindle

11

Hollow shank Short taper

12

adapter cavity

13

Zylindersenkbohrung

15

Guide section, tubular

16

Bearing bore, cylindrical

17

Floor, plan

18

threaded holes

19

inner annular

23

Outer wall, radial

24

Seating region

29

center line

30

driving pins

31

flange

32

Holes, each with 90 ° countersink

33

spigot

34

longitudinal groove

35

transverse groove

36

Spring guide tube

41

Through hole, stepped

42

Longitudinal grooves, keyways

43

Parallel Keys

45

Countersunk screws, four in grinding spindle

46

Ball cage (11 * 24 balls)

47

Circlip in (19)

50

eccentric shaft

51

Bearing section, ground

53, 54

Mass balance section

55, 56

Outer wall, radial

57

recess

58

inner annular

59

Sealing ring, quadring

63

Imbalance recess, e.g. sickle-shaped

64

terminal cover

65

Centerline of the outer wall (55)

71

eccentric

72

Sealing seat section

73

stop collar

74

Bearing seat section

75

threaded portion

76

eccentricity

77

Air guide hole, Gasführbohrung

79

Centerline of (71, 72, 74, 75)

80

Stepped bore, through hole

81

entrainment zone

82

longitudinal grooves

83

puncture zone

84

Spring guide zone

85

Air transfer zone

86

Threaded zone, internal thread

87

retention screw

88

Grub screw, counter-threaded pin

89

center line

100

Grinding disc housing

101

top

102

Inner bore, stepped

103

threaded holes

104

cross holes

111

lower part

112

spigot

113

threaded pin

114

Holes with cylinder counterbores

115

Recess, central

117

Bore, gas guide

121

Sealing ring, lip seal

122

Rolling bearings, deep groove ball bearings

123

shaft nut

125

housing screws

127

Disc springs

130

Freewheel, sprag freewheel

131

inner ring

132

outer ring

133

clamping bodies

134

Grooves in (133)

135

supporting rings

140

sanding pad

141

Face, flat

142

Internal thread, central

143

Oblique holes, holes

145

Ring channel, central

146

Ring channels, decentralized

147

threaded holes

160

Abrasive carrier, elastic

161

top

162

ring lands

163

Mounting holes with cylinder counterbores

164

longitudinal bores

165

Bore, central

167

Bottom with Velcro barb

168

Screws, Allen screws

169

Aufnahmeeindrehung

170

Tool, abrasive, grinding wheel

Claims (8)

Grinding unit with an eccentric shaft (50) arranged in a grinding spindle (10) for supporting a grinding plate (140) carrying an abrasive (170),
characterized, - That on or in the grinding spindle (10) the balanced eccentric shaft (50) is mounted rotationally rigid and longitudinally displaceable, - That on the free end of the eccentric shaft (50) of - in at least one rotational direction relative to the grinding spindle (10) freely movable - sanding pad (140) directly or by means of a sanding pad housing (100) via at least one rolling, sliding or air bearings (122 ) is stored, Sanding unit according to claim 1, characterized in that the grinding spindle (10) has a hollow short shank (11). Sanding unit according to claim 1, characterized in that between the grinding spindle (10) and the eccentric shaft (50), a spring system of at least one spring element (127) is arranged, wherein the spring system acts mechanically or pneumatically. Sanding unit according to claim 1, characterized in that the eccentric shaft (50) has a mass balance section (53, 54). Sanding unit according to claim 4, characterized in that the mass balance section (53, 54) has an imbalance, the unbalance of the eccentric portions (72, 74, 75) of the eccentric shaft (50) and the rotating there bearing parts of the sanding pad (140) - at non-rotating sanding pad (140) - corresponds. Sanding unit according to claim 1, characterized in that a ball cage (46) is arranged radially between the grinding spindle (10) and the eccentric shaft (50). Sanding unit according to claim 1, characterized in that between the grinding spindle (10) and the eccentric shaft (50) a freewheel (130) is arranged. Sanding unit according to claim 1, characterized in that the rolling bearing (122) is a roller bearing according to DIN 635, a self-aligning ball bearing according to DIN 630, a spherical roller bearing according to DIN 635 or a plain bearing of comparable design.

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