US960700A - Crutch-tip. - Google Patents

Description

P. W. PRATT.

GRUTGH TIP.

APPLIOATION FILED APR. 3. 1909.

rammed June 7,1910.

M ATTYE.

w m W P W Du u M P v To all whom it may concern:

UNITED STATES 1 PATENT orrron.

PHILIP W. PRATT, 0F BOSTON, MASSACHUSETTS.

CBUTCH-TIP.

Specification of Letters Patent.

Patented June 7, I910.

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

Be it known that I, PHILIP W. PRA'I'I, of

Boston, in the county of Suffolk and State of Massachusetts, have invented certain new and useful Improvements in Crutch-Tips, of which the following is a specification.

The present invention relates to sockettips of rubber adapted to he slipped upon the ends of crutches toprovide a: cushion therefor and diminish the liability of slip.-

ping.

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 the user, to the circumference of the tread s\ 1rface 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 the tread. Heretofore, where crutch tips without metal plates have been applied di rectly to the ends of crutches or where a metal plate, fiat on its under surface, has been inserted to diminish wear, the pressure of the crutch has been more or less concen-' trated upon the center of the tread of the tip with the result that a hole has been quickly worn through while the outside or periphery of the tread has been hardly worn at a construction and arrangement that the pressure may be transmitted directly to the 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 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 tip in which the bottom of the socket is a central cavity 0 surrounded by a depressed annular bearing zone (Z which bears against the bottom of the socket in the tip. The edges 6 of the plate are turned up slightly so as to avoid liability of cutting into therubber ofwhich the tip is made.

As shown in Fig.1, the crutch tip 6 has formed on the bottom of the internal socket upstanding concentric integral ribs f 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 of felt or similar yielding material whic ,is'

inserted under the metal washer orv plate a.

Preferably the metal plate has on its upper surface a convexity or crown h which is I located at the centerand receives directlfly the pressure of the" end of the, crutch sta 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 suitabie dies shaped so as to press up the center in ed es and to press down the intermediate annu ar 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:

est and cheapest. It 1s therefore the 0b ect of my lnvention to provide a washer or wear-plate of such On account of the fact that the washer the periphery of the tread surface, while 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 concavity 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 rubber toward the center whereby reater resilience and a greater cushioning e ect 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 the crutch staff bears only on the center of ;bears upon the bottom of the crutch tip only. 1 on an annular surface substantially above let 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 desire it to be understood, however, that the concavity in theunder surface of the plate the side of the tip,

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 be comes greater on one side than on the others.

From the above description it will be seen that the essential feature is that the plate It, whatever its method of manufacture, provides for normally maintaining or formmg 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. 1 But when not sub jected 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 a and resilient fingers j. The ring 71 surrounds the crutch above the top of the tip and incloses the upper edge, thereof, while the fingers bear u on the outer surface of the tip a out mi -way between its upper end and the tread surface. These fingersare yielding so as to permit of the pivotal action above describedof the crutch stafl' on the plate h, but at the same time, they prevent the ed eof the tip separating from the crutch, and thus give greater firmness. The inwardly-turned flange It: also prevents matter workin the tip between the we s thereof and the crutch. 4

The turned-up edges e of the plate a act g ard to revent the edges of the crutch stafi P caring and cutting into the rubber at The body portion of the crutch' tip is composed of vulcanized rubber having a suitable egree of elasticity, and the tread face is formed as here shown, by inserting a plug in 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 to each other, and the that shown 1n into the socket of being similar to that shown in the Foster Patent No. 695,298, -nted March 11, 1902. GM side of the plug is embedded in the rubber body before the latter is vulcanized, the convolutions of the plug being secured p ug as a .whole secured to the bodyof the ti b vulcanization.- The plu here shown difi'ers from the Fosterpatent in that its tread face is corrugated and provided with numerous projections and recesses, as shown in Figs. 1 and 2, b subjecting the plu to pressure of a suitab e corrugatmg die be ore the vulcanizing o era'tion. The die forms the depressions an projections while the plug is in a soft condition, these being made per; manent 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 surface. l 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 stri of textile fabric such as canvas, some of t e threads or strands must be presented endwise at the bottom face of the lug. And when the plug is subjected to t e pressure of a die which will produce the de ressions and rojectlons mentioned, such t reads or stran s are more or less condensed lengthwise according to their positions relatively to the a exes of the projections; thatis, those threa 3 whose ends are at the bottoms of the recesses are more shortened and condensed than those whose ends are at the apexes of the projections, while those Whose ends are at the inclined sides of the pro'ections are in an intermediate condition 0 'condensity. The sides ofthe rojections of course face or incline in di erent directions and consequently resent threads which are more or less con ensed andso that their ends are at such an les to the surfaces of the inclines as to alfor the best 0 position to slipping on the surface on whic the lug bears. This is especially useful when t e tip is new because a freshlymolded' tip and plug is more likel to sli than when worn.

W at if c aim is 1. The-combination with a crutch tip, of a pressuresustaining member having a central concavity in its bottom face to form a normal 0 en space at the center of that portion of the tip which receives the pressure of the crutch stad.

2. In combination with a crutch tip, a plate for sustaining the thrust of the crutch stafi', bearing on the bottom of the tip on a zone near its circumference and separated therefrom in its central portion, whereby a washer ha a depressed annular ortion to bear on t e bottom of the tip so et, and a raised central portion, forming a cavity on its under side to permit yielding of the center ofthe tip, and a convex crown on its upper side to take the thrust of the central staff.

4. A washer for socket crutch tips, having an indented or ofiset center and a turned-up periphery, thereby providing in its under surface acentral cavity surrounded by an annular bea g zone, and on the face a central convex crown.

5. In combination with a crutch, a socket upper sur- "crutch, and a holder consisting of a rin surrounding the edge of the tip, and resilient fingers bearing against the sides of the tip for holding the latter adjacent the surface of the crutch.

In testimony whereof I have aflixed my signature, in presence of two witnesses.

' PHILIP W. PRATT. Witnesses:

ARTHUR H. BROWN, P. W. Pnzzm'rl.

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