Rotary abrasive device

May 12, 1964

3,132,452

A. BLOCK

ROTARY ABRASIVE DEVICE

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3,132,452

A. BLOCK

ROTARY ABRASIVE DEVICE

May 12, 1964

Filed Feb. 23, 1962

Sheets-Sheet 2

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United States Patent Office „ 3,132452

Patented May 12, 19S4

3,132,452

ROTARY ABRASIVE DEVICE

Aleck Block, Los Angeles, Calif., assignor io Merit Products, Inc., Los Angeles, Calif., a corporation of California 5

Filed Feb. 23, 1962, Ser. No. 174,961

Claims. (Cl. 51—193.7)

This invention relates to improvements in a rotary abrasive device of the general type exemplified by the io disclosure of the Bonkowski Patent No. 2,439,962.

Such a device has a rotary housing adapted for mounting on a drive shaft and has eight circumferentially spaced longitudinal slots through which corresponding abrasive ribbons extend, which ribbons for example, may 15 be of the general character of sandpaper. Adjacent the eight slots are corresponding brushes extending radially from the housing to back up the exposed ends of the ribbons, the brushes being rearward of the corresponding ribbons with respect to the direction of rotation of the 20 housing.

The abrasive ribbons are wound on a reel sleeve with the inner ends of the ribbons anchored to the periphery of the reel sleeve and the rotary position of the reel sleeve is controlled by an axial control core that telescopes into 25 the reel sleeve into operative engagement therewith. The control core, in turn, is anchored relative to the housing at selected rotary positions by index means comprising a concentric series of latch recesses in the housing engageable by projecting means on the inner end of the control 30 core.

An outstanding advantage of the described construction is that the reel sleeve with the eight abrasive ribbons attached thereto is a replaceable unit that may be readily discarded when the ribbons are used up. A requirement for 35 this feature is that the disposable abrasive unit be of simple inexpensive construction for economy in carrying out abrasive operations. To meet this requirement, the reel sleeve commonly comprises a simple cylindrical cardboard sleeve and the inner ends of the abrasive ribbons are sim- ⁴⁰ply stapled to the cardboard sleeve. For adjustment of the rotary position of the cylindrical reel sleeve by the control core, the reel sleeve is commonly provided with circumferentially spaced slots in its outer end which are engaged by corresponding radial lugs of the control core.

In practice, it has been found that the described arrangement has two shortcomings which prevent full realization of the potential economy. Both of these shortcomings exist because of the pull exerted by centrifugal force on the projected ends of the abrasive ribbons and because of the added tensioning effects of the frictional contact of the abrasive ribbons with the work pieces that are processed.

The first shortcoming is the concentration of stress on the cardboard reel sleeve in the regions where the radial ⁵⁵lugs of the control core engage the end slots of the reel sleeve. The tension stresses in the eight ribbons are additives to accumulate a high magnitude reaction torque on the reel sleeve which is concentrated at the end slots of the sleeve. The reaction torque is at maximum, when θθ the abrasive unit is newly installed because the fully wound reel sleeve places the tangential tension forces at maximum radial distance from the cardboard reel sleeve to create maximum moment arms. If structural failure at the end slots does occur, then, it is likely to occur early in the potential service life of the abrasive assembly.

The second shortcoming is the tendency of the abrasive ribbons to pull free. There is no serious tendency for the inner ends of the abrasive ribbons to separate from the ?θ reel sleeve early in the life of the disposable unit when the reel sleeve is embraced by several layers of the abrasive ribbons. In the first place, the multiple layers tend to tighten to clamp the inner ends of the abrasive ribbon effectively against the reel sleeve. In the second place, the tension in the outer working end of each ribbon is separated from the anchored inner end by multiple turns of the ribbon. As successive increments of the abrasive ribbons are worn and discarded, however, the control core is repeatedly rotated to advance the ribbons, the tightening effect of the multiple turns of the ribbons decreases to decrease the clamping pressure against the inner anchored end of the ribbons. At the same time the tension in the outer end of each ribbon is moved closer to the anchored end. As a result, the shortened ribbons tend to pull free from the staples with consequent economical loss.

The present invention eliminates both of these shortcomings without increasing the cost of the disposable abrasive unit, the result being accomplished by simply changing the shape of the reel sleeve and the cooperating control core. The new reel sleeve is octagonal in cross section and the control core is of corresponding octagonal configuration.

The first shortcoming in concentration of stresses at the end slots of the reel sleeve is avoided because such end slots are eliminated and substantially the whole peripheral area of the control core is in positive engagement with substantially the whole of the interior area of the reel sleeve. The unit stresses involved are so negligible as to remove any possibility of failure of the operative connection between the reel sleeve and the control core.

The second shortcoming in the tendency of the abrasive ribbons to pull free is mitigated because the octagonal configuration of the reel sleeve presents eight longitudinal edges to the encompassing abrasive ribbons. A cylindrical reel sleeve can bend an abrasive ribbon on a radius no greater than the radius of the sleeve but the peripheral longitudinal edges of an octagonal sleeve can be relatively sharp to bend a contiguous abrasive ribbon on an exceedingly small radius. Consequently, frictional resistance to separation of the abrasive ribbons from their anchorages to the reel sleeve is effectively increased to keep the individual ribbons firmly anchored until each ribbon is used to the maximum.

The features and advantages of the invention may be understood from the following detailed description and the accompanying drawings.

In the drawings, which are to be regarded as merely illustrative:

FIG. 1 is a perspective exploded view of the presently preferred embodiment of the invention;

FIG. 2 is a side elevation with portions broken away to reveal concealed structure; and

FIG. 3 is a plan view.

The principal parts of the presently preferred embodiment of the rotary abrasive device illustrated by the drawings include: a rotary drum or housing generally designated 10 having a cylindrical wall 12 and closed at one end by an end wall 14; a reel sleeve 15 positioned axially inside the drum 10; a plurality of eight abrasive ribbons 16 made of emery paper, sandpaper or the like having their inner ends anchored to the reel sleeve by suitable means such as staples 18, the abrasive ribbons being wound on the reel sleeve with their outer ends extending through spaced longitudinal slots 20 in the cylindrical wall 12 of the drum; a corresponding plurality of brushes 22 carried by the drum 10 and extending radially outwardly therefrom to back up the exposed outer ends of the abrasive ribbons 16; a control core 24 that telescopes into the reel sleeve 15 in operative engagement therewith to control the rotary position of the reel sleeve; a disk 25 with a knurled peripheral edge, which disk is united with the control core 24 and which closes the open end of the

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drum 10; a spindle 26 which is mounted axially inside the drum 10 and which is provided with a screw thread 28 on its outer end; and a knurled nut 30 which, engages the screw thread 28 at the outer end of the spindle 26.

The drum or rotary housing 10 is formed with a hub 32 to permit the drum to be mounted on the end of a drive shaft (not shown) and to be secured thereon by a pair of set screws 34 in a corresponding pair of threaded bores 35 in the hub. The cylindrical wall 12 of the drum 10 is formed with longitudinal channels 36 which open radially outwardly adjacent each of the drum slots 20 to mount the brushes 22. Each of the channels 36 has a narrow longitudinal entrance in the form of a slot 38 in the cylindrical drum wall 12. Each of the brushes 22 comprises a bundle of bristles bonded to a base member 40 which base member is dimensioned to slide into a longitudinal channel 36 endwise thereof with the bristles of the brush extending outward through the corresponding slot 38 of the cylindrical drum wall 12. Since the base member 40 is wider than the slot 38, the brushes are effectively interlocked with the drum to prevent separation of the brushes from the drum by centrifugal force. In this particular embodiment of the invention spring metal clips 42 are forced into the channels 36 to exert lateral pressure on the base members 4® to immobilize the base members in the channels.

The reel sleeve 15 is of octagonal cross sectional configuration and may be made of molded cardboard or the like. The octagonal configuration forms eight longitudinal edges 45 on the periphery of the reel sleeve, the eight edges defining eight longitudinal peripheral faces 46. The inner ends of the eight abrasive ribbons 16 are attached to the eight longitudinal faces 46 respectively.

The control core 24 is of similar octagonal configuration to fit snugly but slidably into the reel sleeve to control the rotary position of the reel sleeve. Preferably the leading end of the control core is chamfered as indicated at 44 to facilitate entry of the control core into the octagonal reel sleeve.

Suitable cooperative index means is provided on the drum 10 and the control core 24 to permit the control core to be immobilized relative to the drum at selected rotary positions of the control core. For this purpose the inner surface of the end wall 14 of the drum 10 is formed with a circular series of projections 48 which form a corresponding circular series of radial index recesses 50. The leading end of the control core 24 is formed with four equally spaced radial ribs 52 for releasable engagement with the radial index recesses 5®. As may be seen in FIG. 1, there are twelve of the radial index recesses 50 for engagement by the radial ribs 52, the index recesses being spaced 30° apart.

The reel sleeve 15 with the eight abrasive ribbons 16 attached thereto and wound thereon is an inexpensive disposable unit which is immediately replaced when worn. It is a simple matter to install such a unit by first removing the knurled nut 30 and the disk 25 along with the control core 24. The worn out disposable abrasive unit is removed and is replaced by the new unit. In replacing the new unit the eight abrasive ribbons 16 are disposed as shown in FIG. 2 with the outer ends of the ribbons extending through the slots 20 in the cylindrical drum wall 12. It is to be noted that the outer ends of the eight ribbons extend approximate to or slightly beyond the outer ends of the eight brushes 22, the back faces, i.e. the non-abrasive faces of the ribbons extending adjacent the brushes.

With the new abrasive unit installed in the drum 10, the control core 24 is inserted onto the axial spindle 26 and into the octagonal reel sleeve 15. The indexing ribs 52 of the control member are maneuvered into engagement with the indexing recesses 50¹ to releasably latch the control core 24 relative to the drum 10. At this final position of the control core 24 the disk 25 closes the open end of the drum 10. The knurled nut 30 is then threaded onto the exposed end of the spindle 26 and is tightened to hold the assembly together.

When the operator of the device finds that the exposed ends of eight abrasive ribbons 16 are worn out he stops the rotation of the drum 10 long enough to feed new increments of the eight abrasive ribbons to the eight brushes 22. For this purpose the operator first loosens the knurled nut 30 sufficiently to permit the control core to be withdrawn axially by a slight amount sufficient for the indexing ribs 52 of the control core to disengage from the indexing recesses 50. The operator then grasps the disk 25 by its knurled edge to rotate the reel sleeve counterclockwise as viewed in FIG. 2, the rotation being sufficient to release desired increments of the eight abrasive ribbons 16. The operator then pulls the new increments of the ribbons through the drum slots 20 and tears away the worn ends of the ribbons.

It is apparent that the described construction avoids the shortcomings of prior art devices in the manner heretofore described. The eight relatively sharp peripheral longitudinal edges 45 of the reel sleeve 15 increases the effectiveness of the frictional engagement of the reel sleeve with the ribbons. It is also apparent that since substantially the whole peripheral surface of the control core 24 is in postive engagement with the surrounding octagonal reel sleeve 15, the operative engagement of the control core with the reel sleeve is highly efficient without destructive concentration of stress.

My description in specific detail of the selected embodiment of the invention will suggest various changes, substitutions and other departures from my disclosure within the spirit and scope of the appended claims.