Clamp device for rotary tool element

Abstract: A device for axially clamping a rotary tool element fitted on a spindle of a power driven tool or the like includes a first flange and a second flange. The first flange is mounted on the spindle and has an inner part rotatable with the spindle and an outer part rotatable relative to the inner part about a longitudinal axis of the spindle through a bearing. The outer part includes a first surface for abutting on one end of the rotary tool element. An engaging mechanism is disposed between the inner part and the outer part for limiting rotation of the outer part relative to the inner part within a predetermined angle. The second flange is threadably engaged with a threaded portion of the spindle and includes a second surface for abutting on the other end of the rotary tool element. The second flange is operable to be tightened for clamping the rotary tool element between the second flange and the outer part of the first flange.

Description: The present invention relates to a device for clamping a rotary tool element which is mounted on a sprindle of e.g. an electric power driven tool or a pneumatic tool such as a portable grinder. A conventional device for clamping a rotary tool element of a power driven tool is shown in FIG. 5 and has a first flange 8A and a second flange 9A. The first flange 8A is fitted on a spindle 4A and is rotatable with the spindle 4A. The second flange 9A is screwed on the spindle 4A. In a mounting operation of a rotary blade 7A on the spindle 4A, the rotary blade 7A is fitted on the spindle 4A with its one end surface abutting on the first flange 8A. The second flange 9A is thereafter screwed on a threaded portion 6A of the spindle 4A and is tightened to abut on the other end surface of the rotary blade 7A. Thus, the rotary blade 7A can be removably clamped between the first flange 8A and the second flange 9A. With the conventional clamp device, however, since the rotary blade 7A is only simply clamped between the fixed first flange 8A and the movable second flange 9A through tightening of the second flange 9A screwed on the threaded portion 6A of the spindle 4A, the rotary blade 7A clamped between the first flange 8A and the second flange 9A may be slided or rotated by the load applied thereto during machining operation of a work in the same direction as that for fastening the second flange 9A. Thus, through the frictional force between the rotary blade 7A and the second flange 9A, the second flange 9A is further tightened to increase the clamping force. Meanwhile, in order to change the rotary blade 7A, the second flange 9A is loosened and removed from the spindle 4A. Here, the force (torque) for loosening the second flange 9A is influenced by the frictional force between the second flange 9A and the spindle 4A produced at the threaded portion 6A, and that between the second flange 9A and the rotary blade 7A as well as that between the rotary blade 7A and the first flange 8A. Therefore, in the cutting operation of a work made especially of relatively hard material such as a brick, substantial load is applied to the rotary blade 7A, resulting in that the second flange 9A is firmly tightened. This may cause the rotary blade 7A to be worn out earlier. Meanwhile, the second flange 9A normally includes a plurality of holes for engagement with pins of a wrench which is normally attached to this kind of power driven tool, and the second flange 9A is tightened or loosened through rotation by the wrench. However, in case of loosening of the second flange 9A which is tightened as described above, the rotation of the second flange 9A is frequently difficult. Further, if the wrench is forcibly rotated, the pins or the wrench may be damaged or the holes of the second flange 9A for engagement with the pins may be deformed or enlarged to cause unreliable engagement with the pin, and consequently the device cannot be used further. Additionally, in case a lock device is provided to prevent rotation of the spindle 4A selectively, for ease of loosening of the second flange 9A, the lock device and a gear housing on which the lock device is mounted are damaged by the forced rotation of the second flange 9A. Document US-A-4,637,170 shows a device for clamping a rotational tool element onto a rotary spindle between two flanges. The first flange to be put on the spindle has two parts which can rotate relative to each other. Four camming portions are provided on each part. The relative rotation of the two parts causes the camming surfaces on the one part to come into contact with the camming surfaces on the other part and causes axial movement between the two parts. This results in the first part becoming wedged up against a overhanging flange of the second part. The intention of this is to provide an enhanced coupling with the tool element. However, loosening it still involves having to overcome substantial friction. It is, accordingly, an object of the present invention to provide a device for clamping a rotary tool element of e.g. an electric power driven tool or a pneumatic tool which permits relatively easy loosening of a movable flange in a simple manner for change of the rotary tool element or other operations, while ensuring reliable clamping of the rotary tool element. According to the present invention, there is provided a device for axially clamping a rotary tool element on a spindle of a power driven tool or the like, comprising: a first flange mountable on the spindle and having an inner part to be rotatable with the spindle and an outer part rotatable relative to said inner part about a longitudinal axis of the spindle, said outer part having a surface for abutting one side of the rotary tool element; engaging means disposed between said inner and outer parts for limiting rotation of said outer part relative to said inner part to within a predetermined angle; and a second flange threadably engageable with a threaded portion of the spindle and having a surface for abutting the other side of the rotary tool element, said second flange being arranged, on tightening, to clamp the rotary tool element between said second flange and said outer part of said first flange; characterised in that said inner and outer parts are relatively rotatable through said predetermined angle without axial movement therebetween. The invention will become more fully apparent from the claims and the description as it proceeds in connection with the drawings, which describe the invention by way of example and in which: FIG. 1 is a vertical sectional view of a lower part of a power driven,grinder with a grinding wheel clamped by a clamp device according to an embodiment of the present invention; FIG. 2 is an enlarged sectional view of the device shown in FIG. 1 FIG. 3 is a sectional view taken along line III-III in FIG. 1; FIG. 4 is a sectional view taken along line IV-IV in FIG. 2; and FIG. 5 is a front view of a lower part of a power driven grinder with a grinding wheel clamped by a conventional device. Referring to FIG. 1, there is shown a sectional view of a lower part of a portable power driven grinder having a body G. The body G includes a gear box 1 into which an output shaft 2 of a motor (not shown) extends. A spindle 4 is rotatably supported by bearings 5a and 5b mounted on the gear box 1 and is connected to the output shaft 2 through reduction gears 3. One end of the spindle 4 extends downwardly from the bottom of the gear box 1 and is formed with a threaded portion 6. A flange portion 4a is formed adjacent above the threaded portion 6 and is chamfered at both sides diametrically opposed to each other as shown in FIG. 3. A device for clamping a disc-like grinding wheel 7 includes a first flange 8 and a second flange 9. The first flange 8 is axially displaceably mounted on the spindle 4 and is in engagement with the flange portion 4a for rotation with the spindle 4. The second flange 9 is screwed on the threaded portion 6 and includes a plurality of holes 10 for engagement with a wrench (not shown) which applies rotation to the second flange 9 to tighten the same for clamping the grinding wheel 7 between the first flange 8 and the second flange 9. As shown in FIGS. 2 to 4, the first flange 8 is separated into a cup-shaped inner part 11 and an annular outer part 12 to form a space therebetween for accommodating an annular needle bearing 13 having a plurality of needle rollers 13a disposed in a radial direction and spaced from each other in a circumferential direction. A pair of partly annular protrusions 11a and a pair of partly annular protrusions 12a similar thereto are formed with the inner part 11 and the outer part 12, respectively. The annular protrusions 11a and the annular protrusions 12a extend in an axial direction toward the outer part 12 and the inner part 11, respectively, and are disposed complementary to each other. Here, the pair of the annular protrusions 12a as well as the pair of the annular protrusions 11a are diametrically opposed to each other in a symmetrical manner to form a pair of equivalent clearances therebetween. Each of the protrusions 11a and 12a has a circumferential length shorter than that of each of the clearances, so that the outer part 12 can be rotated relative to the inner part 11 within a predetermined range. Thus, in case the outer part 12 is at a position where each of the pair of the annular protrusions 12a abuts on each one of the annular protrusions 11a disposed in a counterclockwise direction as shown in FIG. 4, a gap 14 is formed between each of the annular protrusions 12a and each of the annular protrusions 11a disposed in a clockwise direction thereof. The inner part 11 of the first flange 8 has at its upper portion a recess 11b which corresponds to the flange portion 4a of the spindle 4 and is in engagement therewith, so that the inner part 11 can rotate with the spindle 4. Further, the inner part 11 has a flanged outer peripheral portion 11c, and the needle bearing 13 is received between the annular protrusions 11a and the outer peripheral portion 11c. The outer part 12 includes a boss portion 12b and a lower planer surface 12c. The grinding wheel 7 is supported by the boss portion 12b with its upper surface abutting on the planer surface 12c. An O-ring 15 is inserted between the outer peripheral portion 11c of the inner part 11 and the outer peripheral surface of the outer part 12. Further, a rubber annular ring 16 is interposed between the inner part 11 and the outer part 12 at a position adjacent the spindle 4. Thus, the O-ring 15 and the annular ring 16 function to seal the space formed between the inner part 11 and the outer part 12 from the outside so as to prevent entry of dust to the space. The O-ring 15 further functions to prevent removal of the outer part 12 from the inner part 11. The surface of the threaded portion 6 of the spindle 4 may be coated with a tetrafluoroethylene or Teflon coating for reducing frictional force with the second flange 9. Similarly, the entire surface of the second flange 9 may be coated with a molybdenum-based coating or is soft-nitrided for reduction of frictional force. The operation of the above clamping device will now be explained. With the first flange 8 fitted on the spindle 4 for rotation therewith through engagement of the flanged portion 4a of the spindle 4 with the recess 11b, the grinding wheel 7 is axially moved on the spindle 4 beyond the threaded portion 6 and is fitted on the boss portion 12b of the outer part 12 of the first flange 8 with the upper surface abutted on the lower surface 12c of the outer part 12. The second flange 9 is thereafter screwed on the threaded portion 6 and is tightened for clamping the grinding wheel 7 between the first flange 8 and the second flange 9 by a desired force (torque). At the beginning of tightening of the second flange 9, the outer part 12 of the first flange 8 as well as the grinding wheel 7 may rotate with the second flange 9. The rotation of the outer part 12 is, however, prevented when the protrusion 12a of the outer part 12 is engaged with the protrusion 11a of the inner part 11 as shown in FIG. 4, and the outer part 12 cannot be rotated further. Therefore, the grinding wheel 7 can be clamped between the outer part 12 of the second flange 9 and the first flange 8 as the second flange 9 is further tightened. To change the grinding wheel 7, the second flange 9 is rotated in a reverse direction so as to be loosened and is thereafter removed from the spindle 4. When the second flange 9 is rotated in the reverse direction for loosening, such force (torque) for loosening may be reduced because of the existence of the needle roller bearing 13 interposed between the inner part 11 and the outer part 12 of the first flange 8. Thus, the needle roller bearing 13 reduces the frictional force between the inner part 11 and the outer part 12 of the first flange 8 to become smaller than that between the outer part 12 and the grinding wheel 7 as well as that between the grinding wheel 7 and the second flange 9. Therefore, the outer part 12, the grinding wheel 7 and the second flange 9 may be rotated together relative to the inner part 11 of the first flange 8 at the beginning of the reverse rotation of the second flange 9. Consequently, the rotational force (torque) depends on the frictional force between the threaded portion 6 of the spindle 4 and the second flange 9 and the frictional force between the inner part 11 and the outer part 12 of the first flange 8, and since such frictional force between the inner part 11 and the outer part 12 is relatively small because of rolling friction, the force (torque) for rotation of the second flange 9 may be reduced. The following experimental results have been obtained for the device of the above embodiment in comparison with the conventional clamp device with respect to the same fastening torque: Additionally, a more excellent result has been obtained by coating the surface of the threaded portion 6 of the spindle 4 with the Teflon coating and/or by coating the entire surface of the second flange 9 with the molybdenum based-coating or by soft-nitriding the same for reduction of frictional force. Although, with the above embodiment, the needle roller bearing 13 is interposed between the inner part 11 and the outer part 12 of the first flange, any other rolling bearings other than the needle roller bearing 13 can be used for permitting rotation of the outer part 12 relative to the inner part 11. While the invention has been described with reference to a preferred embodiments thereof, it is to be understood that modifications or variations may be easily made without departing from the scope of the present invention which is defined by the appended claims.

Claims: A device for axially clamping a rotary tool element (7) on a spindle (4) of a power driven tool or the like, comprising: a first flange (8) mountable on the spindle (4), and having an inner part (11) to be rotatable with the spindle (4) and an outer part (12) rotatable relative to said inner part (11) about a longitudinal axis of the spindle (4), said outer part (12) having a surface (12c) for abutting one side of the rotary tool element (7); engaging means (11a,12a) disposed between said inner and outer parts (11,12) for limiting rotation of said outer part (12) relative to said inner part (11) to within a predetermined angle; and a second flange (9) threadably engageable with a threaded portion (6) of the spindle (4) and having a surface for abutting the other side of the rotary tool element (7), said second flange (9) being arranged, on tightening, to clamp the rotary tool element (7) between said second flange (9) and said outer part (12) of said first flange (8); characterised in that said inner and outer parts (11,12) are relatively rotatable through said predetermined angle without axial movement therebetween. The device according to claim 1 wherein said inner part (11) and said outer part (12) are relatively rotatable through a bearing (13). The device according to claim 2 wherein said engaging means comprise first and second protrusions (11a,12a) formed, respectively, on said inner part (11) and said outer part (12) of said first flange (8), and said first and second protrusions (11a, 12a) are formed to provide therebetween a gap (14) in a circumferential direction to allow the limited rotation of said outer part (12) relative to said inner part (11). The device according to claim 3 wherein said engaging means comprise a pair of said first protrusions (11a) and a pair of said second (12a) protrusions disposed in diametrically opposed relationship with each other, respectively. The device according to claim 3 or 4, wherein: a space is formed between said inner part (11) and said outer part (12) for accommodating said bearing (13); and each of said first and second protrusions (11a, 12a) extends into said space at a position radially inwardly adjacent said bearing (13). The device according to claim 5, wherein a first and a second resilient sealing members (16, 15) are disposed between said inner part (11) and said outer part (12) at a position radially inwardly of said first and second protrusions (11a, 12a) and at a position radially outwardly of said bearing (13), respectively, so as to seal said space from the outside. The device according to any one of claims 3, 4, 5 or 6, wherein: said inner part (11) includes at its peripheral portion an annular flange portion (11c) extending toward said outer portion (12); and said bearing (13) is received between said flange portion (11c) and said first protrusion (11a). The device according to any preceding claims, further comprising a spindle (11) and wherein said threaded portion (6) of the spindle (4) is treated with a Teflon coating or the like for reduction of frictional force between said threaded portion (6) and said second flange (9). The device according to any preceding claim, wherein said abutting surface of said second flange (9), is treated with a molybdenum coating or is soft-nitrided for reduction of frictional force. The device according to any one of claims 2 to 9 wherein said bearing (13) is a needle roller bearing.

Inventors: ABE HIROYUKI, FUSHIYA FUSAO, IBUKI TOMIO, TAKAHASHI YUUJI, TESIMA TOSHIYUKI, ABE, HIROYUKI, FUSHIYA, FUSAO, IBUKI, TOMIO, TAKAHASHI, YUUJI, TESIMA, TOSHIYUKI
Applicants: MAKITA CORP, MAKITA CORPORATION
Application year: 1992
Main classification: B24B45
IPC codes: B24B23, B24B45, B24D7