Abrasive disc subassembly and method of manufacturing same

Abstract: A tool element subassembly, such as an abrasive disc subassembly (17), for mounting to the spindle (15) of a grinder. The subassembly includes an abrasive disc (18), a collar nut (20) and, optionally, a backing flange (22). The central bore (28) in the abrasive disc as well as the hub portion (30) of the collar nut (20) which fits into the bore are both hexagonally shaped to provide a positive drive connection therebetween. The collar nut is either press fit onto the disc or, alternatively, placed directly into the mold for the disc so that the formed abrasive disc is molded directly to the hub portion of thee collar nut. Additional alternative embodiments are also disclosed.

Description: The present invention relates to an apparatus for coupling a tool element, such as a grinding wheel, to the output spindle of a power tool, such as a portable grinder. In particular, the invention relates to an abrasive disc subassembly according to the preamble of claim 1 and to a tool subassembly according to the preamble of claim 6, respectively. Such subassemblies are known from US-A-2 726 493, for example. The grinding wheel used on portable grinders generally consists of an abrasive disc having a centrally located bore for receiving an internally threaded collar nut. The collar nut has a hub portion that fits into the bore in the grinding wheel so that the enlarged hex-shaped head portion of the collar nut abuts the underside of the grinding wheel. The collar nut is adapted to be mounted to the externally threaded spindle of the grinder. Typically, a support flange is positioned on the spindle between the grinding wheel and an annular shoulder formed on the spindle to provide backing support for the grinding wheel. The support flange is typically comprised of a metal stamping that is configured to engage the backside of the abrasive disc around its outer radial end. The direction of rotation of the spindle when the grinder is energized is such that the collar nut will self-thread onto the spindle until a tight frictional engagement is provided between the support flange and the grinding wheel. The grinding wheel can then be further tightened onto, or subsequently removed from, the spindle by applying a wrench to the collar nut. Such assemblies are referred to hereafter as conventional abrasive disc subassemblies. In the prior art of US 2 726 493 (Young et al), an abrasive disc subassembly is shown, in which a liner is interposed between the disc and the collar nut. In use the collar nut becomes a permanent part of the wheel and is disposed of with a worn wheel. With conventional abrasive disc subassemblies the central bore in the abrasive disc through which the spindle extends is circular in shape. Similarly, the hub portion of the collar nut that fits into the bore of the disc is also circular in cross-section. The collar nut in such conventional assemblies is not permanently affixed to the abrasive disc, but rather is intended to be reused when a worn disc is replaced. In addition to the possibility of losing or misplacing the collar nut, this type of assembly is further disadvantageous from the standpoint that replacement abrasive discs must have properly sized bores, which are not uniform for all brands and models. Moreover, the application of driving torque from the spindle to the abrasive disc is solely through the frictional interfaces between the abrasive disc and the supporting flange and the supporting flange and the spindle. Consequently, under load the abrasive disc subassembly may slip at either of these frictional interfaces. To combat slippage, abrasive disc subassemblies are frequently tightened onto the spindle to such a degree that subsequent removal becomes difficult. To alleviate these problems, various "hubbed"-type abrasive disc subassemblies have been proposed, such as that shown in US patent No 4 494 615 to Mackay, Jr. Hubbed-type abrasive disc subassemblies include a backing flange that is permanently affixed to the backside of the abrasive disc by the hub portion of the collar nut which thus becomes an integral part of the subassembly. The entire subassembly is thus intended to be discarded when the disc is worn. Hubbed-type grinding wheels are generally intended to be used in combination with specially designed support flanges adapted for engaging driving surfaces on the backing flange affixed to the disc. With each of the known forms of grinding wheel subassemblies, driving torque is transferred from the output spindle of the grinder to the grinding wheel via a frictional coupling, either between the output spindle and the grinding wheel directly, or through an intermediary support flange which either frictionally engages the backside of the grinding wheel or a backing flange permanently affixed thereto. Frictional couplings of the above-described type without support flanges are prone to slippage, or in the alternative, must be tightened to such a degree as to subsequently make it difficult to remove a worn wheel. While the hubbed-type grinding wheels are much less susceptible to slippage problems, they are substantially more expensive than conventional non-hubbed grinding wheels and consequently are not as widely used. Accordingly, there is need for an improved grinding wheel subassembly that provides a positive means of coupling the grinding wheel to the spindle of the grinder without the expense of the hubbed-type wheel subassemblies. In addition, it is desirable to provide such an improved grinding wheel subassembly that can be readily manufactured as a hubbed or a non-hubbed grinding wheel and can be used with or without a support flange. Furthermore, it is desirable to provide a grinding wheel subassembly that is compatible with both United States and European safety standards. According to a first aspect of the invention, an abrasive disc subassembly for a grinder having an externally threaded motor driven spindle, comprises an abrasive disc having a centrally located bore formed therethrough, and a collar nut having a hub portion adapted to fit into said bore in said abrasive disc and configured so as to preclude relative rotation therebetween and an integral enlarged head portion, said collar nut having an internally threaded bore formed therethrough that is adapted for threadably engaging said spindle in a rotational direction opposite the direction of rotation of said motor-driven spindle and said enlarged head portion including hexagonally shaped means for receiving a torque-applying tool for enabling the tightening of said subassembly onto said spindle and the subsequent removal of the tightened subassembly from said spindle wherein driving torque is transferred from said spindle to said abrasive disc through said collar nut, whereby the walls of the bore and the external walls of the hub portion are parallel to the axis of rotation of the spindle, characterised in that the bore and the hub portion are both hexagonally shaped. According to a second aspect of the invention, a tool subassembly for a power tool having an externally threaded, motor-driven spindle, comprises a tool element having a centrally located bore formed therethrough; a collar nut having a hub portion having an external shape of substantially identical size to said bore in said tool element and a hexagonally shaped integral enlarged head portion; and means for affixing said hub portion of said collar nut in said bore of said tool element so as to preclude relative rotation therebetween; said collar nut further having an internally threaded bore formed therethrough that is adapted for threadably engaging said spindle to couple said tool subassembly to said spindle, whereby the walls of the bore (28) and the external walls of the hub portion are parallel to the axis of rotation of the spindle, characterised in that the bore and the hub portion are both hexagonally shaped. Additional objects and advantages of the present invention will become apparent from a reading of the following detailed description of the preferred embodiments which make reference to the drawings in which: Figure 1 is a perspective view of a typical power tool to which the teachings of the present invention may be applied; Figure 2 is an elevational, sectional detailed view of the right-angle spindle of the tool shown in Figure 1, illustrating a first embodiment of a tool subassembly according to the present invention; Figure 3 is a plan view of an abrasive disc; Figure 4 is a plan view of a collar nut; Figure 5 is a side view of the collar nut shown in Figure 4; Figure 6 is an elevational, sectional detailed view of the right-angle spindle of the tool shown in Figure 1, illustrating a second embodiment of a tool subassembly according to the present invention; and Figure 7 is an elevational, sectional detailed view of the right-angle spindle of the tool shown in Figure 1, illustrating a third embodiment of a tool subassembly according to the present invention. With reference to Figure 1, there is illustrated a portable electric grinder 10 with which the teachings of the present invention may be applied. It will be appreciated by those skilled in the art, however, that the grinder 10 is only exemplary of a wide variety of power tools to which the invention may be applied. With this in mind, the grinder 10 generally comprises a motor housing 11, a switch handle 12, a gear case 13, an auxiliary handle 14, and a right-angle spindle 15 for mounting a grinding wheel subassembly or other tool element subassembly. The guard for the grinder has been removed in Figure 1 for the sake of clarity. With further reference to Figure 2, the spindle 15 is externally threaded and has an annular shoulder 16 formed thereon. A tool element subassembly, or abrasive disc subassembly 17, is threadably mounted on the spindle 15. The abrasive disc subassembly includes a depressed centre abrasive disc 18 that is coupled to an internally threaded collar nut 20. It should be noted at this point that while the preferred embodiments are described and illustrated in combination with depressed center abrasive discs; the present invention is equally applicable to flat "type 1" abrasive discs as well. The abrasive disc subassembly 17 is supported in Figure 2 by a supporting flange 22 that is positioned on the spindle 15 of the grinder so that the central portion 24 of the flange abuts the annular shoulder 16 of the spindle. In addition, the support flange 22 is typically configured so that the outer distal and portion 26 supports the backside of the abrasive disc 18 radially outward of the depressed center portion of the abrasive disc 18 as shown. Due to the direction of rotation of the spindle 15 relative to the threads on the spindle, when the grinder is energized the collar nut 20 of the subassembly 17 will self-thread onto the spindle until the backside of the abrasive disc 18 bears against the distal end portion 26 of supporting flange 22. Support flange 22 thus also provides a frictional drive coupling between the spindle 15 of the grinder and the abrasive disc 18. With additional reference to Figures 3 - 5, the abrasive disc 18 and collar nut 20 components of the tool element subassembly 17 according to the present invention are shown. The abrasive disc 18 in the preferred embodiment illustrated in Figure 3 is provided with a hexagonally shaped central bore 28, rather than the conventional circular bore. In addition, the collar nut 20 is formed with a corresponding hexagonally shaped hub portion 30 that is adapted to be press fit into the bore 28 in the abrasive disc 18. In particular, the collar nut 20 in the preferred embodiment shown in Figures 4 and 5 includes a first hexagonally shaped hub portion 30 which, as noted, is precisely sized to tightly fit within the correspondingly configured hexagonal central bore 28 in the abrasive disc 18. The enlarged hexagonally shaped head portion 32 of the collar nut 20 is integrally formed with the hub portion 30 in an angularly offset manner relative to the hexagonal hub portion 30 to maximize the contact area between head portion 32 and the underside of the abrasive disc 18. In particular, as best shown in Figure 4, the hex-head portion 32 is angularly offset thirty degrees relative to the smaller hex-hub portion 30 such that the apexes of the hex-hub 30 are radially aligned with the midpoints of the flats of the hex-head portion 32 and vice versa. This particular relationship between the two integral hex portions of the collar nut 20, however, is not critical to the function of the present invention. Accordingly, it will be appreciated that when the abrasive disc subassembly 17 according to the present invention is threaded onto the spindle 15 of the grinder, a positive drive coupling is created between the spindle 15 and the abrasive disc 18 due to the hexagonal-shaped interface between the hub portion 30 of the collar nut 20 and the abrasive disc 18. In other words, because the abrasive disc 18 in the subassembly 17 of the present invention is precluded from rotating relative to the collar nut 20, it no longer becomes necessary to rely upon the frictional interface between the spindle 15 and the abrasive disc, either directly or via a backing flange, to transmit rotational torque from the spindle 15 to the abrasive disc. Moreover, due to the fact that abrasive discs 18 are typically formed in a press via a molding process, it does not add to the cost of manufacture to form a hexagonal-shaped bore in the abrasive disc rather than a circular bore. It will be appreciated that other means for affixing the collar nut 20 to the abrasive disc 18 can be used. Specifically, in addition to the press fitting method previously described, the hub portion 30 of the collar nut 20 may be deformed after insertion into the bore 28 in the abrasive disc 18, or a portion of the hub material deflected, to create a mechanical locking engagement between the collar nut and the abrasive disc. Additionally, an adhesive may also be used if desired. As previously noted, a preferred method of manufacturing the abrasive disc subassembly 17 according to the present invention contemplates press fitting the hub portion 30 of the collar nut 20 into the bore 28 of the abrasive disc. In this manner the collar nut 20 can be tightly secured to the abrasive disc 18 without materially altering the production process for the abrasive disc. Alternatively, the collar nut 20 can be inserted directly into the abrasive disc mold during the molding process so that the abrasive disc 18 is formed directly to the hub portion 30 of the collar nut 20. Turning to Figure 6, a further alternative construction of the abrasive disc subassembly 17 according to the present invention is shown. In this embodiment, the hub portion 30 of the collar nut 20 is modified so as to extend above the top surface of the abrasive disc 18 when installed. An annular recess is formed in this extended portion 34 for receiving a snap ring 36 as shown to prevent removal of the collar nut 20 from the abrasive disc 18. In this embodiment, it is not as critical that the hub portion 30 of the collar nut 20 be sized precisely to conform to the hex-bore 28 in the abrasive disc 18. Referring now to Figure 7, a further alternative embodiment of the present invention is shown. In this embodiment the subassembly 17 is modified to include a permanently affixed backing flange to the backside of the abrasive disc 18. In particular, it will be noted that the collar nut 20 in this embodiment is formed with an integral tubular extension 38 which extends from the hub portion 30 of the collar nut 20. The backing flange 40 is comprised of a metal stamping that includes a distal end portion 42 that is adapted to contact the backside of the abrasive disc 18 radially outward from the depressed center portion so that the backing flange 40 is spaced away from the abrasive disc 18 radially inward of the distal end portion 42. The central part of backing flange 40 forms an upstanding neck portion 44 that defines a cylindrical recess for receiving the tubular extension 38 of the collar nut 20. The neck portion 44 is appropriately sized so that it can be press fit onto the tubular extension 38 of the collar nut 20, thereby fixedly joining the two components. The upper end of the neck portion 44 is preferably formed with an inwardly extending shoulder 46 that defined a circular opening 48 appropriately sized to receive the end portion of the spindle 15 below the annular shoulder 16. In this manner, when subassembly 17 is threaded onto the spindle 15, the shoulder portion 46 of the backing flange 40 bears against the annular shoulder 16 on the spindle 15. In addition, since the collar nut 20 in this embodiment is tightly secured to the backing flange 40, it is not necessary for the abrasive disc 18 to also be press fit onto the hub portion 30 of the collar nut 20 in order to secure the collar nut to the subassembly 17.

Claims: An abrasive disc subassembly (17) for a grinder (10) having an externally threaded motor driven spindle (15), comprising an abrasive disc (18) having a centrally located bore (28) formed therethrough, and a collar nut (20) having a hub portion (30) adapted to fit into said bore in said abrasive disc and configured so as to preclude relative rotation therebetween and an integral enlarged head portion (32), said collar nut (20) having an internally threaded bore formed therethrough that is adapted for threadably engaging said spindle (15) in a rotational direction opposite the direction of rotation of said motor-driven spindle and said enlarged head portion (32) including hexagonally shaped means for receiving a torque-applying tool for enabling the tightening of said subassembly (17) onto said spindle (15) and the subsequent removal of the tightened subassembly from said spindle; wherein driving torque is transferred from said spindle (15) to said abrasive disc (18) through said collar nut (20), whereby the walls of the bore (28) and the external walls of the hub portion are parallel to the axis of rotation of the spindle, characterised in that the bore and the hub portion are both hexagonally shaped. A subassembly according to claim 1, wherein the hexagonal shape of said hub portion (30) is angularly offset thirty degrees relative to the hexagonal shape of said head portion (32). A subassembly according to Claim 1, characterised in that it further includes a flange member (40) having an outer radial portion (42) contacting the backside of said abrasive disc (18) and an inner radial cylindrical portion (44) having an inside diameter greater than the diameter of said spindle (15); and in that said collar nut (20) further includes an integral extension (38) extending from said hub portion above the backside of said abrasive disc and having a maximum external diameter substantially equal to the inside diameter of said inner radial cylindrical portion (44) of said flange member, such that said inner radial cylindrical portion (44) of said flange member is adapted to be press fit onto said extension (38) of said collar nut (20) and thereby affix said flange member (40) to the backside of said abrasive disc. A subassembly according to Claim 1 further including means for affixing said collar nut to said abrasive disc. A subassembly according to Claim 4, characterised in that said hub portion of said collar nut is adapted to be press fit into said bore in said abrasive disc. A tool subassembly for a power tool having an externally threaded, motor-driven spindle (15), comprising a tool element having a centrally located bore formed therethrough; a collar nut (20) having a hub portion (30) having an external shape of substantially identical size to said bore in said tool element and a hexagonally shaped integral enlarged head portion (32); and means for affixing said hub portion (30) of said collar nut (20) in said bore (28) of said tool element so as to preclude relative rotation therebetween; said collar nut (20) further having an internally threaded bore formed therethrough that is adapted for threadably engaging said spindle (15) to couple said tool subassembly to said spindle, whereby the walls of the bore (28) and the external walls of the hub portion are parallel to the axis of rotation of the spindle, characterised in that the bore and the hub portion are both hexagonally shaped. A tool subassembly according to Claim 6, characterised in that said collar nut (20) is adapted to threadably engage said spindle (15) in a rotational direction opposite the direction of said motor-driven spindle. A tool subassembly according to Claim 6, characterised in that said hub portion (30) of said collar nut (20) is adapted to be press fit into said bore (28) in said tool element. A tool subassembly according to Claim 6, characterised in that said affixing means comprises a snap ring (36) that is adapted to engage an annular groove formed in an end of said hub portion (30) projecting above the bore in said tool element. A tool subassembly according to one of Claims 6 to 9, characterised in that said tool element comprises an abrasive disc (18). A tool subassembly according to any one of Claims 6 to 10, characterised in that the hexagonal shape of said hub portion (30) is angularly offset 30 degrees relative to the hexagonal shape of said head portion (32).

Inventors: TIMMONS RUSSEL M, TIMMONS, RUSSEL M.
Applicants: BLACK & DECKER INC, BLACK & DECKER INC.
Application year: 1992
Main classification: B24D5
IPC codes: B24D5, B24B45