Crutch-tip.

Application filed April 3, 1909. Serial No. 487,795.

To all whom it may concern:

Be it known that I, Philip W. Pratt, of Boston, in the county of Suffolk and State of Massachusetts, have invented certain new 5 and useful Improvements in Crutch-Tips, of which the following is a specification.

The present invention relates to socket tips of rubber adapted to be slipped upon the ends of crutches to provide a' cushion 10 therefor and diminish the liability of slipping.

It consists in a wear plate or washer of metal which is so shaped as to transmit the pressure of the crutch, due to the weight of 15 the user, to the circumference of the tread surface of the tip so that the wear will be distributed over the tread surface more generally than has heretofore been the case, instead of being localized at the center of 20 the tread. Heretofore, where crutch tips without metal plates have been applied directly to the ends of crutches or where a metal plate, flat on its under surface, has been inserted to diminish wear, the pressure 25 of the crutch has been more or less concentrated upon the center of the tread of the tip_ with the result that a hole has been quickly worn through while the outside or 30 °f the tread has been hardly worn

It is therefore the object of my invention to provide a washer or wear plate of such construction and arrangement that the pressure may be transmitted directly to the 35 outer edges of the bearing surface under all conditions of use and regardless of the direction in which the crutch staff may extend with respect to the ground or floor.

In the accompanying drawings, Figure 40 1 represents a sectional view of a socket crutch tip having a wear plate or washer embodying the features of my invention inserted therein. Fig. 2 represents a similar view of a somewhat different type of socket ⁴⁵ tip in which the bottom of the socket is plain and has inserted a felt washer. Fig. 3 represents a.perspective view of the metal plate. Fig. 4 represents a fragmentary view of the end of a crutch with my improved 50 tip applied thereto.

The same letters of reference indicate the same parts in all the figures.

As shown in the drawing, the plate or washer a is set into the socket of a crutch ⁵⁵ tip δ resting upon the bottom of the latter. This plate is formed on its under side with a central cavity c surrounded by a depressed annular bearing zone d which bears against the bottom of the socket in the tip. The edges e of the plate are turned up slightly eo so as to avoid liability of cutting into the rubber of which the tip is made.

As shown in Fig. 1, the crutch tip & has formed on the bottom of the internal socket upstanding concentric integral ribs f 65 of rubber which are adapted to yield more than a solid body of rubber would do, so as to give a cushioning effect. In Fig. 2 the bottom of the socket is plain and the cushioning effect is given by a washer g of 70 felt of similar yielding material which, is inserted under the metal washer or plate a.

Preferably the metal plate has on its upper surface a convexity or crown h ivhich is located at the center and receives directly 75 the pressure of the end of the. crutch staff. . The preferred manner of making the washer is to cut the circular disks from comparatively thin sheet metal and subject the disks to pressure between suitable dies 80 shaped so as to press up the center in edges and to press down the intermediate annular zone. This, of course, is not the only way in which the washers could be formed but is preferable on account of being the quick- 85 est and cheapest.

On account of the fact that the washer bears upon the bottom of the crutch tip only : on an annular surface substantially above the periphery of the tread surface, while 80 the central part is raised above the bottom of the tip, the pressure transmitted when any weight is applied to the crutch, acts principally upon the periphery of the tread. This is due to the fact that the con- 95 cavity allows the central part of the tip bottom to rise and to press slightly upon the ground while the heavy pressure is borne by the edges of the tread. The concavity also allows a stretching or flowing of the 100 rubber toward the center whereby greater resilience and a greater cushioning effect in the tip is given. These effects are intensified by the fact that the upper edge of the plate is convex above the concavity so that 105 the crutch staff bears only on the center of the plate. . Thereby, whatever the inclination of the crutch may be when the tip strikes the ground, the pressure will be transmitted to the edges of the tread. I 110 desire it to be understood, however, that the concavity in the under surface of the plate ©60,700 is mainly instrumental in producing this effect, and that the plate which is flat on its upper surface but having the cavity underneath. would also produce similar results. The concavity allows the bottom of the tip to shape itself to the form of the plate and thereby vield centrally, equalizing the wear over the entire tread surface. The convexity on the upper surface of the plate allows a certain amount of oscillation of the tip bottom in any direction so as to give an approximately even bearing on the ground when the crutch staff is inclined and thereby increase the wear and diminish the tendency to slip. It also allows the tip to be more easily turned when the wear becomes greater on one side than on the others.

From the above description it will be seen that the essential feature is that the plate h,' whatever its method of manufacture, provides for normally maintaining or forming a space at the center of that portion of the tip which receives the pressure of the crutch staff. By “ normally ” I mean that under some pressures the bottom of the crutch tip may perhaps be pressed up so as to close said space. But when not subjected to heavy pressure there is always a space at the center of the tip so that said tip may yield centrally as hereinbefore mentioned.

In order to retain the upper rim of the socket against the sides of the crutch staff, I provide a spring holder consisting of a ring i and resilient fingers j. The ring i surrounds the crutch above the top of the tip and incloses the upper edge thereof, while the fingers j bear upon the outer surface of the tip about mid-way between its upper end and the tread surface. These fingers are yielding so as to permit of the pivotal action above described of the crutch staff on the plate Λ, but at the same time, they prevent the edge of the tip separating from the crutch, and thus give greater firmness. The inwardly-turned flange k also prevents matter working into the socket of the tip between the walls thereof and the crutch.

The turned-up edges e of the plate a act as a guard to prevent the edges of the crutch staff nearing and cutting into the rubber at the side of the tip. ... .

The body portion of the crutch tip is composed of vulcanized rubber having a suitable degree of elasticity, and the tread face is formed, as here shown, by inserting a plug m> partially into the base of the body portion, said plug being formed from a strip of textile fabric, such as canvas, suitably treated on its sides with rubber cement and wound spirally to form a disk, the sides of which are formed by the edges of the convolutions of the strip, this form of plug being similar to that shown in the Foster Patent No. 695,298, granted March 11, 1902. One side of the plug is embedded in the rubber body before the latter is vulcanized, the convolutions of the plug being secured 70 to each other, and the plug as a whole secured to the body of the tip by vulcanization. The plug here shown differs from that shown m the Foster patent in that its tread face is corrugated and provided with 75 numerous projections and recesses, as shown in Figs. 1 and 2, by subjecting the plug to pressure of a suitable corrugating die before the vulcanizing Operation. The die forms the depressions and proj ections while the plug 8 0 is in a soft condition, these being made per_rmanent by the vulcanization of the plug. A plug of textile fabric formed as shown in the Foster patent, presents a surface which is less liable to slip, than a rubber 85 surface. I have found that by corrugating the base of the plug as described, its liability to slip is still further decreased. By the employment of a strip of textile fabric such as canvas, some of the threads or strands 90 must be presented endwise at the bottom face of the plug. And when the plug is subjected to the pressure of a die which will produce the depressions and projections mentioned, such threads or strands are more 95 or less condensed lengthwise according to their positions relatively to the apexes of the projections; that is, those threads whose ends are at the bottoms of the recesses are more shortened and condensed than those 100 whose ends are at the apexes of the projections, while those whose ends are at the inclined sides of the projections are in an intermediate condition of condensity. The sides of the projections of course face or 105 incline in different directions and consequently present threads which are more or less condensed and.so that their ends are at such angles to the surfaces of the inclines as to afford the best opposition to slipping on 110 the surface on which the plug bears. This is especially useful when the tip is new because a freshly molded tip and plug, is more likely to slip than when worn.