GB2407286A

GB2407286A - Attaching abrasive sheet to a grinding tool

Info

Publication number: GB2407286A
Application number: GB0422970A
Authority: GB
Inventors: Thomas Demuth
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2003-10-20
Filing date: 2004-10-15
Publication date: 2005-04-27
Anticipated expiration: 2024-10-15
Also published as: GB2407286B; GB0422970D0; CN1608799B; CN1608799A; DE10349275A1

Abstract

In a grinding tool which has a grinding platen 22, two opposite ends 25 of an abrasive sheet 24 are each attached to the platen 22 by means of a respective rocker 34 and clamping member 42. Each rocker 34 is located on the platen 22 with a first end 36 close to the edge 28 and a second opposite end 38 inwardly thereof. An end of the abrasive sheet 24 is attached to the platen by placing it over a rocker 34 and then moving the respective clamping member 42 so that the end of the sheet 24 is held between the second end of the rocker 34 and the clamping member 42. Continued movement of the clamping member 42 pivots the rocker 34, lifting its first end 36 from the platen 22 and thereby enabling tension to be applied to the abrasive sheet 24.

Description

R.307181 20.10.03.Dt/Mi ROBERT BOSCH GMBH, 70442 Stuttgart Hand-held

grinding tool

Prior art

The present invention takes as its starting point a hand- held grinding tool according to the precharacterising clause of Claim 1.

According to DE 101 39 548 Al, a hand-held grinding tool is known which is provided with a system for tensioning and tautening an abrasive sheet to be held on its grinding plate underside. This system operates extremely reliably and is easy to handle. It projects over the rear edge of the grinding plate and therefore makes it difficult to grind flush with the edge when grinding stepped areas and the like using the rear edge of the grinding plate.

With this system, it is therefore only possible to grind flush with the edge using the front edge of the grinding plate.

The hand-held grinding tools disclosed in US 6,648,08, which are constructed as oscillating grinding machines, are provided with rockerlike clamping levers at opposite grinding-plate edges on the grindingplate upper side, which can be used to fix the abrasive-sheet ends on the outer-edge side, between the lever arm on the outer edge and the grindingplate upper side. The respective clamping lever is to be actuated manually on the side remote from the edge.

In this, an easily accessible tensioning arm arranged in the grindingplate cover serves to open the rocker-like clamping lever for the purpose of removing or inserting an abrasive-sheet end, whereby the abrasive sheet can only be held by the known clamping means without also being tattered against the underside of the grinding plate.

Thus, when grinding with a grinding plate which is moved to and fro, there is a considerable slip between the abrasive sheet and the grinding plate, which has an adverse effect on the grinding action and can cause the abrasive sheet to wear prematurely as a result of kinks forming and the abrasive layer therefore becoming detached.

Advantages of the invention The invention having the features of Claim 1 is advantageous in that an economical, light, hand-held grinding tool is provided, which can be used with both the front and the rear edge flush with the edge for grinding and whereof the abrasive sheet can be reliably clamped and tattered on the grinding plate using particularly simple means. The abrasive sheet employed in the invention is a flexible grinding sheet that can easily be wrapped around the edges of the grinding plate.

As a result of the fact that the clamping means constructed as a rocker lies, pre-tensioned by a spring, with its lever arm which is close to the edge on the upper side of the grinding plate and the lever arm which is remote from the edge projecting upwards, the abrasive-sheet end on the upper side of the rocker being fixable on the lever arm which is remote from the edge and then being pivotable downwards together with said lever arm so that the region of the abrasive sheet which is close to the edge can be drawn upwards, whereupon the rocker can be blocked with the lever arm remote from the edge pivoted downwards, an abrasive-sheet tensioning system which is known per se and has hitherto been used only for tonglike clamping can be used to tension the abrasive sheet tautly with little modification but in an essentially new association with said abrasive sheet.

As a result of the arrangement of blocking means which press the abrasivesheet end against the lever arm remote from the edge and fix it thereon, i.e. as a result of the fact that the abrasive-sheet end can be fixed between the lever arm which is remote from the edge and a tensioning arm adjustably supported against said lever arm, reliable clamping and improved Hastening of the abrasive sheet is possible using a previously known - slightly modified - kinematic principle.

As a result of the fact that the clamping means do not project beyond the grinding-plate ends here, but are instead arranged within the grinding-plate ends, the hand- held grinding tool enables easily controllable grinding which is flush with the edge at both ends of the grinding plate.

As a result of the fact that the tensioning arm transmits a pivotal stroke to the lever arm which is remote from the edge and thereby tautens the abrasive sheet, the tensioning and tautening of the abrasive sheet can be realised by actuating a single operating element which moves the tensioning arm.

As a result of the fact that the clamping means and the tensioning arm are arranged substantially symmetrically on both opposing grinding-plate ends, both abrasive-sheet sides can be tensioned and tautened in the same, particularly operationally reliable, manner.

As a result of the fact that the rocker and the tensioning arm are substantially the same width as the abrasive sheet, this latter can be clamped particularly reliably to prevent it from becoming detached.

As a result of the fact that the lever arm remote from the edge, on which the abrasive sheet is fixed, has a transverse groove for pressing in the abrasive sheet and also for the form-fitting insertion of the tensioning arm, the clamping of the abrasive-sheet end is secured with a greater pressure force.

As a result of the fact that the tensioning arm and the lever arm which is remote from the edge have a friction- increasing coating in the contact region with the abrasive sheet, the abrasive sheet can be clamped even more securely.

Drawing The invention is explained in more detail below with reference to an exemplary embodiment with an accompanying drawing, which shows: Fig. 1 a schematic side view of the hand-held grinding tool in the region in which the abrasive sheet is clamped) Fig. 2 a hand-held oscillating grinder with a further variant of the tensioning of the abrasive sheet; Fig. 3 a hand-held oscillating grinder with another variant of the tensioning of the abrasive sheet; Fig. 4 the plan view of a rocker as a detail) and Fig. 5 the plan view of a tensioning arm as a detail.

Exemplary embodiment of the invention Fig. 1 shows a side view of a handheld grinding tool 10 as a detail. Its grinding plate 22 can be seen in the region of its front edge 28 with an abrasive sheet 24 held on it.

The abrasive sheet 24 is wrapped around the underside of the grinding plate 22 and its front edge 28 and is guided over its upper side 26. Here, the abrasive-sheet end 25 lies on a rocker 34, guided firstly over the lever arm 36 which is close to the edge and over its lever arm 38 which is remote from the edge and being pressable into a transverse groove there 39 by a tensioning arm 49 fitting in the transverse groove 39 with form fit, said transverse groove having a friction-increasing coating (not illustrated in more detail). By rotating the turning knob 43 and moving its rotational tensioning lever 42 axially downwards about its axis of rotation 44, the abrasive-sheet end 25 is fixed between the tensioning arm 49 and the transverse groove 39 such that it is prevented from becoming unintentionally detached and, by moving the rotational tensioning lever 42 further downwards, the rocker 34 is pivoted clockwise. During this, the lever arm 38 which is remote from the edge moves down to the upper side 26 of the grinding plate 22 and the lever arm 36 which is close to the edge pivots upwards away from the upper side 26, pushing the abrasive sheet 24 guided over it upwards and tautening it. During this, the rocker 34 moves about a pivot axis 40. The turning knob 43 having the axis of rotation 44 and the tensioning arm 49 is mounted in the housing 12 in the region of a plate-like grinding-plate cover 32. The grinding-plate cover 32 and the grinding plate 22 are coupled resiliently together by way of connecting means (not illustrated in more detail).

To release the abrasive sheet 24, the turning knob 43 is rotated such that the rotational tensioning lever 42, constructed as a threaded pin, moves axially upwards. The rocker 34 follows it with its lever arm 38 which is remote from the edge - pre-tensioned by a pressure spring 35 - and arrives back in its starting position which is remote from the upper side and points obliquely upwards.

If, when the tension on the abrasive sheet is released, the tensioning arm 49 moves upwards out of the transverse groove 39, the abrasive-sheet end 25 or the entire abrasive sheet 24 can then easily be removed from it.

That lever arm 36 of the rocker 34 which is close to the edge has a slight bend or angle 37 so that, when the lever arm 36 which is close to the edge is pivoted upwards, the contact surface of the abrasive sheet 24 is increased and the abrasive sheet does not tear there.

Fig. 2 shows a side view of a hand-held grinding tool 10 which is constructed as a hand-held oscillating grinder and has a housing 12 which receives a motor (not illustrated in more detail) and, at the rear, merges into a handle 14 in which a manually operated push-button 14 is mounted such that it can be pressed in, an electric connection cable leading into its rear end.

Held at the bottom of the housing 12, as seen in the viewing direction, there is a grinding plate 22 which can have an abrasive sheet 24 tensioned on its underside. The abrasive sheet 24 is wrapped around the front and rear edge 28, 30 of the grinding plate 22 by means of its abrasive sheet ends 25 and is fixed on the upper side 26 of the grinding plate by way of the rocker 34 and a pressure pin 48 and simultaneously tensioned. In principle, the rocker 34 is constructed as shown in Fig. 1, although somewhat simplified, its release position being indicated by continuous lines and its tensioning position being indicated by dot-and-dash lines. In the release position, or in the insertion position for fitting an abrasive sheet 24, that lever arm 36 of the rocker 34 which is close to the edge is supported - pre-tensioned downwards by a spring - against the upper side 26 of the grinding plate 22, the lever arm 38 which is remote from the edge extending to the right such that it is approximately parallel with the upper side 26 of the grinding plate 22. After being inserted over the rocker 34, the abrasive-sheet end 25 is firstly fixed on the upper side of the lever arm 38 remote from the edge as a result of moving the pressure pin 48 downwards by actuating a rotational tensioning lever 42, and the rocker 34 is actuated as the pressure pin 48 is lowered further.

During this, that lever arm 38 of the rocker which is remote from the edge is lowered downwards to the upper side 26 of the grinding plate 22. During this, its lever arm 36 which is close to the edge pivots upwards away from the upper side 26 of the grinding plate 22 and pushes the abrasive sheet 24 upwards, tautening it. The same procedure is to be repeated at the rear edge 30 of the grinding plate 22 with the other abrasive-sheet end 25, so that the abrasive sheet 24 then lies against the underside of the grinding plate 22, tensioned up to its tearing limit, at both ends. When the oscillating grinder 10 is operated, it is therefore possible to achieve only a minimum slip and maximum efficiency. The rocker 34 is rotatably mounted in a pivot axis 40 on the upper side 26 of the grinding plate with a bearing lug 41 in a bearing-block-type arrangement, whilst a torsion spring (not illustrated in more detail) attempts to pivot the rocker 34 to the left as seen in the viewing direction. In a grinding-plate cover 32 extending parallel to the grinding plate 22 as part of the housing 12, the rotational tensioning lever 42 is pivotably and axially adjustably arranged in a thread and can be easily pivoted back into its starting position by way of a rotational pressure/torsion spring 46.

Like Fig. 2, Fig. 3 shows an exemplary embodiment of the hand-held grinding tool 10 in which, instead of the turning knob 43, a tensioning arm 49 mounted on the grinding plate cover 32 is used in conjunction with the pressure pin 48 and, acting as an eccentric lever, presses the abrasive- sheet end 25 onto that lever arm 38 of the rocker 34 which is remote from the edge during the tensioning procedure and, pivoting further, carries this abrasive-sheet end pivotally to the right. During this, the lever arm 36 which is close to the edge pushes the abrasive sheet 24 upwards in the end region and at the same time tautens it on the underside of the grinding plate 22.

The pivot lever 52 is mounted in the grinding-plate cover 32 such that it can pivot about a pivot axis 54 and, in the tensioning position, is supported by its cam 58 on both the abrasive-sheet end 25 and the lever arm 38 which is remote from the edge, and can push this latter downwards as far as the stop on the upper side 26 of the grinding plate 22.

The abrasive sheet 24 is thus tautened in the manner described.

At the rear edge 30, the abrasive-sheet end 25 is illustrated merely schematically; however, it is symmetrical with the arrangement at the front edge 28 and is constructed and actuated in the same manner.

Fig. 4 shows a plan view of the rocker 34 as an individual moulded wire part, particularly a round wire. The front lever arm 36, which is close to the edge, is shorter than the lever arm 38 which is remote from the edge and the bearing lugs 41 are constructed as stamped parts.

Fig. 5 shows the rotational tensioning lever 42 as a detail, its tensioning arm 49 extending over the entire width of an abrasive sheet and being provided for form fitting insertion into the transverse groove 39 in the rocker 34 - preferably as a round wire part. The pressure pin 48 of the rotational tensioning lever 42 is constructed as a threaded pin with a coarse thread and is axially adjustable in a corresponding guide in the housing 12 or the grinding-plate cover 32 and can be latched in its rotational end positions. A rotational movement results in the abrasive sheet 24 being axially adjusted and tensioned and - in the opposite direction - released.

By constructing a rocker 34 from an elastic resilient material, it is possible to pre-select the tautness of the abrasive sheet 24 and the resultant paper tension such that it is impossible for the abrasive sheet 24 to tear as a result of being pulled too taut.

Claims

Claims 1. A hand-held grinding tool (10) having a grinding plate (22) on

the underside of which an abrasive sheet (24) can be mounted, said abrasive sheet surrounding two mutually opposing grinding-plate edges (28, 30) with its ends (25) and being fixable thereon or on the upper side of the grinding plate (22) at both ends by clamping means which are constructed close to the edge as a rocker (34), characterized in that the abrasive sheet (24) can be fixed by its abrasive-sheet ends (25) on the respective region remote from the edge using clamping means (38, 48, 49, 58) and can be moved upwards on the region close to the edge and thereby tautened.
2. A hand-held grinding tool according to Claim 1, characterized in that the abrasive sheet (22) can be fixed above the upper side (26) of the grinding plate (22) on the rocker (34) and, fixed thereon, can be pivoted together with this in tautening manner.
3. A hand-held grinding tool according to Claim 1 or 2, characterized in that the rocker (34) is arranged within the contour of the grinding-plate edges (28, 30) and can be actuated within this contour, tautening the abrasive sheet (24).
4. A hand-held grinding tool according one of the preceding claims, characterized in that the rocker (34), pre-tensioned by a spring, lies with its lever arm (36) which is close to the edge on the upper side (26) of the grinding plate (22) and thus projects upwards with the lever arm (38) which is remote from the edge, the abrasive- sheet end (25) on the upper side of the rocker being fixable on its lever arm which is remote from the edge and being pivotable downwards with said lever arm - fixed thereon - so that the region of the abrasive sheet (24) which is close to the edge can be moved upwards away from the upper side (26) of the grinding plate (22) and is thus variably blockable.
5. A hand-held grinding tool according to any one of the preceding claims, wherein as a result of the fact that the abrasive-sheet end (25) can be fixed between the lever arm (38) which is remote from the edge and a tensioning arm (48, 49, 58) which is adjustably supported against said lever arm, the abrasive sheet (24) is secured in captive manner in a first tensioning step.
6. A hand-held grinding tool according to one of the preceding claims, characterized in that, after the abrasive-sheet end (25) has been clamped, the tensioning arm (48, 49, 58) transmits a pivotal stroke to that lever arm (38) of the rocker (34) which is remote from the edge, thereby pivoting the rocker (34).
7. A hand-held grinding tool according to one of the preceding claims, characterized by a double - substantially symmetrical - arrangement of the clamping means (38, 39, 48) and the tensioning arm (49, 58) on both opposing grinding-plate edges (28, 30).
8. A hand-held grinding tool according to one of the preceding claims, characterized in that the rocker (34) is substantially as wide as the abrasive sheet (24).
9. A hand-held grinding tool according to one of the preceding claims, characterized in that that lever arm (38) of the rocker (34) which is remote from the edge and the tensioning arm (49) have friction-increasing coatings in the contact region with the abrasive-sheet end (25).
10. A hand-held grinding tool according to one of the preceding claims, characterized in that the lever arm (38) which is remote from the edge has a transverse groove (39) for the form-fitting insertion of the tensioning arm (49) and the abrasive sheet (24).
11. A hand-held grinding tool substantially as herein described with reference to the accompanying drawings.