US 2990661 A
Description (OCR text may contain errors)
July 4, 1961 D. P. HACKETT BACKING DISK FOR ABRASIVE SHEET 2 Sheets-Sheet 1 Filed July 10, 1958 INVENTOR. DONALD Pf/ACKETI 2 M QM ATTORNEY D. P. HACKETT BACKING DISK FOR ABRASIVE SHEET July 4, 19 1 2 Sheets-Sheet 2 Filed July 10, 1958 ,INVENTOR. DONALD PhAc/arz' ATTORNEY United States Patent 2,990,661 BACKING DISK FOR ABRASIVE SHEET Donald P. Hackett, 325 Pennsylvania Ave., Plymouth, Ind. FiledJuly 10, 1958, SenNo. 747,605 2 Claims. ((51. 51-197) This invention relates to improvements in backing disks for abrasive sheets, and more particularlyto a power driven rotary disk having a face thereof spanned by an abrasive sheet adapted to be pressed against the face of a work piece to smooth or abrade said surface.
The primary object" is to provide a backing disk of this character which is simple in construction, inexpensive, easy to use, strong in structure, light in weight, readily mounted. and dismounted from a drive member and accommodating rapid application of an abrasive sheet thereto and removal of an abrasive sheet therefrom.
A furtherobject is to. provide a backing disk' of this character having a plurality of ribs, having sheet abutting portions lying in substantially a common plane and having intervening offset portions, each provided with an aperture remote from the edge of the disk to accommodate air flow through the space between said offset portion and an abrasive disk or sheet carried by said backing disk. I
A further object is to provide adevice of this character formed of heat conductive material and providing a support for an abrasive sheet at spaced points of that sheet and accommodating air flow between said abrasive sheet and intervening portions of said backing disk, whereby rapid heat transfer can occur from the working surface engaged by said abrasive sheet and from said abrasive sheet. n A further object is to provide a rotatable backing disk with a plurality of ribs adapted to support an abrasive sheet and intervening offset portions forming air pockets having air passages at the inner portions thereof and having recessed outer edges between said ribs to facilitate air flow into said pockets.
A further object is to provide a rotatable backing disk for abrasive sheets, having a plurality of sheet contacting ribs extending from the central portion to the periphcry of said disk, and intervening offset portions, together with a. recessed central portion receiving the head of a member for securing the abrasive sheet to the disk, and acentral reinforcement for said disk to rigidify the same, wherein said ribs are so shaped and proportioned as to facilitate batting and grinding of a work surface and to reduce choking of the abrasive surface of the abrasive sheet. by paint and soft metal forming a part of" that surface by virtue of freedom of portions of said sheet between. said ribs from contact with said backing disk. l A further object is to provide a rotatable backing disk for abrasive sheets which is adapted to be driven at high speed, which provides support for said backing sheet at limited areas of said sheet including narrow areas extending from. the center to the edge thereof and which exposes to air for cooling purposes the portions of the back of the sheet intervening between said last named narrow disk portion.
Other objects will be apparent from the following specification.
In the drawing:
FIG. 1 is a perspective view of a backing disk mounted upon a power tool and supporting an abrasive sheet in operative position thereon;
FIG. 2 is a face view of the backing disk having an abrasive sheet applied thereto which abrasive sheet is cut away at a part to expose said backing disk;
FIG. 3 is an edge view of the backing disk having an abrasive sheet supported thereon;
2,990,661 Patented July 4, 1961 FIG. 4 is an edge view of a modified embodiment of the invention illustrating the mounting of a backing sheet thereon;
FIG. 5 is an enlarged sectional view taken on line 5-5 of FIG. 2;
FIG. 6 is a fragmentary face view of a modified form of the backing disk;
FIG. 7 is a fragmentary detail sectional view taken on line 77 of FIG. 6;
FIG. 8 is a face view of another modified embodiment of the backing disk; and
FIG. 9 is a fragmentary detail sectional view taken on line 99 of FIG. 8. 1
Referring to the drawing which illustrates the preferred embodiments of the invention, the numeral 10 designates a rotatable power driven shaft upon which my improved backing disk is adapted to be mounted. The shaft 10 may be driven in any suitable manner, and in the form selected for illustration said shaft 10 constitutes the output shaft of a power driven hand tool having a motor housing 12 and grip portions 14 and 16 and a shaft journaling sleeve or collar 18, from which the end of the shaft 10 projects in the usual manner.
My improved backing disk 20 is formed of rigid sheet metal or plate stock or of any suitable rigid strong material preferably having the property of rapid heat transfer. I prefer to use sheet metal, such as steel or an aluminum alloy which is of substantially uniform thickness throughout. The disk 20 is of generally circular outline but is preferably provided with a plurality of spaced recessed or scalloped edge portions 22 preferably equally spaced and similar. Rib or sheet-contacting portions 24 are arranged symmetrically and extend from the outer edge of the disk 20 between adjacent scallops or recesses 22 and the inner portion or central portion of the-disk. As here shown the portions 24 extend substantially radially and are of substantially uniform cross sectional configuration throughout their length, but it will be understood that said portions 24 need not be straight nor radial nor of uniform cross-sectional shape along their length and need not extend continuously from the center to the edge of the disk. The crest portions of the ribs 24 are positioned outwardly with respect to the position in which the disk is mounted on the shaft 10 and lie substantially in a common plane to provide a planar backing. or support at a plurality of points of an abrasive sheet 26. The abrasive sheet may be the usual sandpaper, emery cloth or other material of sheet character having abrasive particles adhered to one surface thereof. The central portion of the disk 20 is preferably cupped as by theprovision of a frusto conical wall portion 28 and a central wall portion 30 rearwardly offset from the plane of the crest of the ribs 24. The disk has a central opening. therein to receive the shank 32 of a securing member, suchas a securing screw which is screw-threaded in a central bore 34 formed in the end of the shaft 10. The securing member preferably has a thin flat head portion 36 whose axial dimension is less than the amount. of the offset 28 and which preferably is of large size compared to the diameter of the shank 32 so as to accommodate overlapping and marginal clamping of a substantial portion of the abrasive sheet 26 at the center thereof, as best seen in FIG. 5.
The segmental portions 40 of the disk 20 between the ribs 24 are rearwardly offset from the peripheral edge of said disk to a point adjacent to but spaced from the disk offset 28, thereby providing an annular portion 42 of the disk which is substantially coplanar with the crests of the ribs 24. Each segmental offset 40 has an aperture 44 formed therein at the inner portion thereof adjacent to the annular portion 42.
If desired, the disk 20 may be reinforced at the center thereof by a reinforcing plate or sheet 50, as illustrated at FIG. 4, which reinforcing plate may be welded or otherwise suitably secured to the disk.
The abrasive sheet 26 is secured to the backing disk 20 concentrically thereof by means of the securing member 32, 36, as illustrated at FIG. 5, with the abrasive surface thereof outermost or oppositely oriented with respect to the backing sheet so as to engage the work surface in the manner well understood in the art. The anchoring of the sheet at the recessed portion 28, -30 of the disk tends to deform the abrasive sheet 26, but upon application of said sheet to a working surface the sheet tends to assume substantially flat form at the marginal portion thereof, as illustrated in FIGS. 3, 4 and 5, with the back face of the abrasive sheet 26 bearing against the annular portion 42 of the disk and the crests of the ribs 24.
In the use of the device, as the abrasive sheet is applied to the working surface, the sheet accomplishes the desired butfing, grinding or surfacing operation in the conventional manner, and accomplishes this work as rapidly as the work is accomplished by the use of prior known backing disks which provide greater surface area or contact between the abrasive disk and themselves. In other words, despite the fact that the portions of the sheet 26 which register with the segmental offsets 40 lack direct backing from the disk, the abrasive sheet serves satisfactorily the grinding and buffing function intended for it, and accomplishes that function as rapidly as it can now be accomplished by the use of other types of backing disks.
As the backing disk and abrasive sheet mounted thereon are rotated by the power driven shaft during the application thereof to the working surface, air is free to fiow in the segmental passages between the sheet 26 and the segmental disk portions 40 and for the full depth of said segmental portions by reason of the provision of the central openings 44. In other words, air flows between the peripheral edge of the disk and the openings 44. The recessed or scalloped configuration of the edge portions 22 of the disk serve to enhance or facilitate air flow into the passages between the sheet 26 and the offset disk portions 40 because the radially projecting portions at the ribs of the scalloped edges define air scoops at the periphery of the disk. This air flow serves to carry away the heat generated by the buffing or grinding or other surfacing operation incident to the contact of the abrasive with the work pieces. The heat is carried away effectively because a large portion of the abrasive sheet is directly exposed to the flow of air therepast. Likewise the heat which passes through the abrasive sheet from the working surface to the disk at the ribs 24 and annular portion 42 thereof is readily dissipated by this air flow passage. Still a further efliciency of heat dissipation is accomplished by reason of the turbulence of the air at the back surface of the disk incident to rotation of the disk.
I have found that by the use of a disk of this character the elfective life of an abrasive sheet of conventional character is greatly increased, that is, is increased many fold. In other words, whereas abrasive sheets commonly have a very short life when applied to bufiing, grinding and polishing operations when done by power driven tools, their life and full efiectiveness remain or continue as much as sixfold longer than usual when used with a backing sheet of this character. I attribute this increase of effective life to the disk configuration and to undamped vibration which occurs during use incident to contact of the abrasive sheet with the work principally at the rib backed parts of the sheet incident to the application of grinding pressure during use and to the rapid dissipation of heat generated by the abrading operation. In other words, the bonding agent for the abrasive upon the abrasive sheet is protected against loss of efficiency due to high heat generation and therefore retains and bonds or adheres the abrasive particles for much longer periods of time than occur in cases where the heat of the opera- 4 tion is not dissipated suificiently rapidly to avoid deterioration of the bonding properties of the bonding agent.
Another interesting characteristic of abrasive sheets mounted upon my improved backing disk is that they tend to be self-cleaning. It is a common experience of the users of abrasive sheets operated by power to find that the sheets clog rapidly and lose their abrasive properties when working on work pieces having paint surfaces or having soft metal portions upon the working surfaces, such as portions of solder or brass. These materials, such as soft metal or paint seem to choke up the abrasive surface of the sheet and to seat in cavities between abrasive particles upon the sheet, thereby destroying the abrasive efiiciency of the abrasive sheet. This choking action is not experienced when abrasive sheets are applied to my improved backing disk, as in cases where the abrasive sheet is used in bufling and grinding automobile panels to be refinished. This advantage results from the vibration mentioned above and the fact that, when any tendency toward such choking action occurs, it can be corrected by applying the abrasive sheet against a steel surface free of paint, solder and other clogging material and operating the backing disk to rotate the same for a short period of time until the backing disk and the abrasive sheet have vibrated enough to rid the abrasive face of the abrasive sheet of accumulated clogging material. The abrasive sheet so applied against a sheet of steel tends to clean itself rapidly and to restore its abrasive eflicieney when mounted upon my improved disk. Thus it is possible to accomplish a bufling and grinding operation more rapidly than can be done with abrasive sheets mounted upon conventional backing disks, because the operator is not required to stop the work periodically for the purpose of replacing disks which have choked due to collection of paint and soft metal in the abrasive surface thereof.
One additional advantage of the construction is its light weight resulting from its fabrication from thin stock. This is advantageous from the standpoint of reducing the efiort or energy required during use thereof and from the standpoint of reduction of the mass thereof to a minimum for the purpose of maintaining at a minimum the heat storage capacity thereof. The reduction of heat storage capacity facilitates the rapid heat dissipation which has been mentioned above.
The ribs may be formed of different cross-sectional configurations. Thus in the construction seen in FIG. 3, the ribs 24 have substantially flat crest portions providing an area of contact between the same and the disk 26. Such fiat faced ribs are not required, however, and instead the ribs may be of curved cross-setcional shape, as illustrated at 24' in FIG. 4. I have found that the backing disk is substantially equally efiicient in both configurations of the ribs.
Another embodiment of the invention is illustrated in FIGS. 6 and 7 wherein the openings 44 between the ribs 24 of the disk are enlarged, and the area of the offset portions 40 of the disk between the ribs 24 is reduced. This construction provides a large area of opening for access of air to the back of the disk and at the same time maintains the rigidifying and supporting function of the offset portions 40 of the disk.
It is not essential that the device maintain the shape of a disk, and instead the device may assume the shape of a star wheel or a spider, as illustrated in FIG. 8, wherein the metal between the rib or spoke portions 24 is cut away completely. The parts 24 are bent transversely to define marginal flanges projecting angularly from the plane of the disk and of the abrasive sheet which bears thereagainst similarly to the arrangement shown in FIG. 4. In this instance the cross-sectional configuration or curvature of the parts 24, together with the high speed of operation by the power driven tool, are relied upon to maintain the necessary rigidity and support for the abrasive sheet- While the preferred embodiments of the invention have 5 been illustrated and described, it will be understood that changes in the construction may be made within the scope of the appended claims without departing from the spirit of the invention.
1. A backing member for an abrasive sheet, c0mprising a thin member of substantially uniform thickness throughout formed of shape-retaining sheet metal having a central aperture and a plurality of integral elongated oifset ribs extending from the central portion to the edge of said member, said ribs projecting substantially the same distance and in the same direction from one face thereof and being arranged in substantially equi-angular and equispaced relation to contact the back face of a substantially flat abrasive sheet at spaced narrow elongated portions and thereby expose the intervening portions of the back face of said sheet to air, said member having apertures therein between said ribs, the edges of said member between said ribs having concave curved edge portions.
2. A rotatable power-driven backing disk for an abrasive sheet, comprising a thin metal plate of substantially 6 I uniform thickness having a plurality of elongated ofiset rib portions extending from the edge to the central portion of said member and adapted to engage and support spaced narrow elongated portions of an abrasive sheet, the portions of said member intervening between said ribs being offset from the plane of said sheet to provide air passages behind said sheet, and an aperture formed in each offset portion spaced from the periphery of said member, said ribs being of substantially uniform crosssectional shape throughout their length and said offset portions being of tapered shape from their outer to the inner ends and having concave curved edge portions between said ribs.
References Cited in the file of this patent UNITED STATES PATENTS 2,331,861 Smith Oct. 12, 1943 2,410,812 Michel Nov. 12, 1946 2,527,762 Pratt Oct. 31, 1950 2,556,434 Mitchell June 12, 1951 2,819,568 Kasick Ian. 14, 1958