Title:
Manufacture of graded shoe lasts
United States Patent 2394780


Abstract:
This invention relates to the grading of shoe lasts and the object is to provide an improved grading method which ensures that the toe spring and heel heights and the relationship between the lines, angles and contours of the original model are faithfully preserved in the graded models. The...



Inventors:
Arnold, Iredale John
Application Number:
US49290843A
Publication Date:
02/12/1946
Filing Date:
06/30/1943
Assignee:
Arnold, Iredale John
Primary Class:
Other Classes:
142/1
International Classes:
B27M3/20
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Description:

This invention relates to the grading of shoe lasts and the object is to provide an improved grading method which ensures that the toe spring and heel heights and the relationship between the lines, angles and contours of the original model are faithfully preserved in the graded models.

The present invention is based on the discovery that the toe spring and heel heights and other essential characteristics of the original lastmodel can be faithfully preserved in the graded models by turning the latter on the grading machine so that, in each graded model, the ball point and all other points along the curved bottom line extending from the point of the toe to the heel breast point will be spaced below a straight line running from said toe point to said breast point exactly the same distance as the corresponding points on the curved bottom line of the original model. The manner in which this is accomplished will now be described with reference to the accompanying drawings, in whichFig. 1 illustrates the "off grade" relationship between a size 4 original master model and a size 8 model which has been graded from the master model in the conventional manner.

Fig. 2 is a view showing the outline and certain dimensional characteristics of a size 4 master model from which all the graded models shown in the remaining figures are assumed to be graded.

Fig. 3 is a composite diagrammatic view showing how a size 8 model graded in accordance with my invention compares with a size 8 model graded from the size 4 master model by the customary grading procedure.

Fig. 4 is a view showing how a size 2 last graded in accordance with my invention compares with a size 2 last graded from the same original master model by the customary grading procedure.

Fig. 1 illustrates the "off grade" relationship existing between a size 4 original model and a "hand broken" size 8 model which has been graded from the original model by the conventional machine grading and "hand breaking" procedure. This view shows that the toe springs and heel heights a and b of the size 8 blank are substantially greater than the toe spring and heel heights a' and b' of the original model. It also shows that the higher heel required by the graded model is incorrectly pitched so that its tread is tipped upwardly at the front edge instead of lying parallel with the ground as in the original model. The size 8 last blank is not graded directly from the original model but is graded from a previously graded size 6 which has been "hand broken" to reduce the toe-spring height. However, since each change of grade in accordance with the conventional grading procedure varies the toe and heel spring heights of the graded model as compared with the pattern model it follows that the toe and heel spring heights of the size 8 which is graded from the size 6 pattern model will be substantially greater than the toe spring and heel heights of the original size 4 master model. The size 8 blank illustrated in Fig. 1 is one that has been graded from a size 6 which has been "hand broken" at the vamp line, only, to correct for excessive toe spring height. In most cases the last manufacturer will also "break" the heel part of the size 6 model to lower the heel height and thus reduce the disparity between the heel height of the original size 4 master model and the sizes which are graded up from the "hand broken" size 6. However, the limitations of the conventional grading methods are such that the heel height of the graded size 8, even when graded from a size 6 which has been "hand broken" at both the vamp and heel parts, will be appreciably greater than the heel height of the original size 4 model. This makes it very difficult for the heel maker to produce heels that will tread properly when fitted to the size 8 and other models which are graded upwardly from the "hand broken" size 6 model. As previously stated "breaking" of the pattern model at both the vamp and heel portions also results in length and contour changes which complicates the work of the pattern maker in fitting patterns to the altered models and other models which are graded upwardly therefrom.

The foregoing difficulties as regards fitting patterns and heels to "hand broken" models and models graded therefrom also apply in the case of "hand broken" models in sizes below size 4. In other words, resort to the "hand breaking" process to increase the toe spring and heel heights of the smaller sizes also produces distorted and "off grade" models which not only require corrective measures on the part of the pattern maker and heel maker but also make it impossible to produce, on the altered models, shoes which faithfully preserve all the essential and desirable characteristics of shoes made on the perfect size 4 original master model.

In the case of the size 4 model shown in Fig. 1 the line c-d represents the vertical distance from the ball point to a diametrically opposite point on a straight line e-f extending from the toe point to the heel breast point. This distance is appreciably less than the corresponding distance, g-h, between the ball point and a diametrically opposite point on the straight line i-j extending from the toe point to the heel breast points of the size 8 model. Other vertical distances measured between diametrically opposite points on the straight line e-f and the underlying curved bottom line of the size 4 model will also be less than the vertical distance between corresponding diametrically opposite points on the straight line i-- and the underlying curved bottom line of the size 8 blank. These dimensional differences between the size 4 and size 6 models are responsible for their variations as regards toe spring and heel height and are eliminated in lasts made in accordance with my invention.

In Fig. 4 a size 2 last, graded from a size 4 original model in accordance with my invention, is shown in comparison with a "hand broken" size 2 last graded from the same original master model by the customary grading procedure. In this view the outline of the last graded in accordance with my invention is identified by numeral 5 while the outline of the conventionally graded last is identified by the numeral 6. When the model 5 shown-in Fig. 4 is compared with the size 4 master model shown in Fig. 2, it will be seen that, in both cases, the vertical distance c"-d" from the ball to a diametrically opposite point on the line e"-f" is exactly the same and this is also true of all other vertical distances between the line e"-f" and the underlying curved bottom line as measured at corresponding points on the two models. It therefore follows that the toe spring and heel heights of model 5 (Fig. 4) are exactly the same as the original size 4 master model (Fig. 2). On the other hand, it will be noted that the vertical distance between points c"-d" of model 6 (Fig. 4) is less than the distance between the corresponding points c"-d" of model 4 (Fig. 2). All other vertical distances measured between points on the line e"-f" and diametrically opposite points on the underlying curved bottom line of model 6 will also be less than the vertical distance measured between corresponding points along the line e"-f" and the underlying curved bottom line of the size 4 master model.

In Fig. 4 the extent to which the curved bottom line running from the toe point e" to the heel breast point f" of model 6 is displaced upwardly with reference to the curved bottom line running from the toe point e" to the heel breast point f of model 5 represents what, for lack of a better term, is hereinafter referred to as the "undergrade" of the conventionally graded size 2 model identified by reference numeral 6. It is this "undergrade" which is responsible for the differences between the toe and heel heights of the conventionally graded size 2 model and the toe and heel heights of the master model (Fig. 2) from which it is graded. The "hand breaking" process ordinarily resorted to to correct this difference between the toe and heel heights of the master model and the size 2 last which is graded therefrom in the conventional manner has the effect of distorting the size 2 last so that it no longer preserves all the desirable and essential characteristics of the master model. In the case of the size 2 model graded in accordance with my invention the "undergrade" characteristic of the conventional graded size 2 model is eliminated so that correct toe spring and heel heights are obtained without resorting to the "hand breaking" process or to any equivalent process which in any way disturbs the correct relationship between the lines and contours of that portion of the graded model which lies above the straight line which is obtained by producing the line e"-f" (Fig. 4) to the heel end of the model.

In Fig. 3 a size 8 last model, graded in accordance with my invention from a size 4 original master model (Fig. 2) is shown in comparison with a "hand broken" size 8 blank graded from the same original model by the customary grading procedure. In this view the size 8 graded in accordance with my invention is indicated at 7 while the conventionally graded blank is indicated at 8. The distance between the points c'-d' of the graded model identified by the numeral 7 is the same as the distance between the corresponding points c-- of the master model shown in Fig. 2 and the same is true of all other vertical distances between the line e--f and the underlying curved bottom line as measured at corresponding points on the two models here referred to, namely model 7 shown in Fig. 3 and the master model shown in Fig. 2. On the other hand, it will be noted that the vertical distance between the points H. G. of blank 8 shown in Fig. 3 is considerably greater than the vertical distance between the corresponding points c-d of the master model shown in Fig. 2.

The extent to which the curved bottom line 3 running from the toe point to the heel breast point of blank 8 projects below the curved line running from the toe point to the heel breast point of model 7 represents what may be termed the "over-grade" of blank 8 which is compensated for in the conventional grading process by the "hand breaking" process and which is entirely eliminated in the size 8 model graded in accordance with my invention.

From the foregoing it will be seen that, according to my invention, all graded models are turned on the last lathe or grading machine so that the distance between any selected point on a straight line extending from the toe point to the heel breast point of the graded model and a diametrically opposite point on the underlying curved bottom surface of said model will be exactly the same as the distance between correspondingly located points of the original model from which the graded model is graded. It will thus be seen that my invention eliminates the "undergrade" and "overgrade" characteristics of the smaller and larger sized models which are graded in accordance with conventional practice and therefore eliminates the main source of trouble experienced in connection with producing true "on-grade" smaller and larger sizes from an original master model. Since my invention eliminates the off-grade characteristics of graded last models, as heretofore produced, it also eliminates the necessity of resorting to the "hand breaking" process or any equivalent process which permit the toe and heel heights of the graded models to be corrected only at the expense of serious distortion at points which cause trouble to the pattern maker.

The grading of lasts in accordance with my invention is accomplished in the following manner: Lasts which are graded upwardly from the original master model are first turned on the last lathe grading machine in the usual manner.

The "overgrade" previously referred to is then removed by a further turning operation in the course of which the partly formed last is oscillated in an arcuate path of suitable length instead of being turned through a complete circle of revolution as occurs during the original turning operation. During the oscillating movement of the last the engaging cutter travels along the curved bottom line extending from the toe point e to the heel breast point f and, in so doing, removes additional material from the bottom portion of the last so that, on completion of this second turning operation, the distance from any point along the line e-f to a diametrically opposite point on the underlying curved bottom surface of the last will be the same as the distance between correspondingly located points of the original master model. This same technique cannot be followed exactly in connection with the machine grading of lasts which are graded down from the original master model. In the latter case it is necessary to first increase the size of the pattern model by attaching a pad to the curved bottom surface of the pattern model which extends from the toe point e to the heel breast point f. The attachment of this pad to the pattern model ensures that, during the initial turning of the smaller size last more material is left on the turned last along the curved bottom line extending from e to I. A suitable proportion of this excess material is then removed by a second stage turning operation in which the last being graded is oscillated through an arc of suitable length instead of being caused to describe a complete circle as occurs during the initial turning operation. By suitably regulating the amount of excess material which is left on the bottom of the smaller size graded models due to the attachment of the pad to the pattern model and then carefully controlling the proportion of this excess material which is removed during the second stage turning operation, it is possible to produce down graded models in which the distance from any selected point on the line e-f to a diametrically opposite point on the underlying curved bottom line will be exactly the same as the distance between correspondingly located points of the master model.

In both of the above mentioned cases the oscillating movement which is imparted to the model being graded during the second stage grading or turning operation is accomplished in the following manner. The belt and pulley drive which is employed for continuously rotating the pattern model and the work during the first stage grading operation is replaced during the second stage grading operation by a rack and pinion drive which oscillates the pattern model and the work through an arc of suitable length, the rack and pinion drive being adjustable to vary the length of said arc in accordance with the width size of the model being graded.

I claim: The method of upgrading lasts from a master model which comprises first turning the work on a last grading lathe to provide a last blank of a size larger than that of the original master model, determining the amount of material to be removed from the bottom of the blank, oscillating the blank and simultaneously with said oscillation removing said predetermined amount of material from the toe point to the heel breast point for the full length and width of the bottom portion only of the resulting blank to reduce the vertical distances between a straight line extending between said points and opposite points on the curved bottom surface underlying said straight line to make said vertical distances the same as in correspondingly located points on the master model.

JOHN ARNOLD IREDALE.