Last design system for mass produced footwear

Abstract

A template for use in making a last on which to form a shoe, the template representing the outline shape of the underside of a foot, including a heel portion 3, a toe portion, a maximum width portion

Description

FIELD OF THE INVENTION This invention relates to the design of lasts for use in mass produced footwear. BACKGROUND OF THE INVENTION When the footwear industry moved from bespoke footwear made by craftsmen to footwear produced in quantities, it became clear that in order to provide a range of customers with the footwear that fitted them the shoes needed to be produced in a range of sizes and three major standardised sets of sizes emerged, so-called English, Continental and American. Details of the systems are found at https: / / en.wikipedia.org / wiki / Shoe size. These systems and others choose a different base measurement from which to work, and follow different dimension increments between successive shoe sizes. Base measurements used include the average length of the foot which fits comfortably in the shoe, the length of the inner cavity of the shoe and the length of the last on which the shoe is manufactured. It is also necessary to provide in any such system when applied to the practical manufacture of shoes, in addition to the overall shoe size (based on the length of the foot), to make the shoes available in a number of different widths or, alternatively expressed, in a number of different girths, girth being the circumferential measurement around the foot in a plane substantially perpendicular to the long axis of the foot itself. The traditional way of making a last is to start with tracing round the foot standing on a sheet of material such as heavy card placed on a flat surface, to produce an outline shape and smoothing that outline around the toe area to provide a smooth curve. Separately an outline of the shape of the foot seen from the side is made, and by assembling two shapes cut from the sheet material along such outlines, and with the shape corresponding to the shape of the foot seen from above lifted at the heel region depending on the heel height desired, the plan and elevation shapes of a last can be taken and applied to a block of carveable material, traditionally wood, to produce a last form once the edges are rounded off. In both cases, the outlines are of an irregular asymmetric shape with a curvature varying continuously around the entire contour. The shape of lasts used in commercial mass manufacture has similar properties, i.e. the intersection of a plane with the body of the last is an outline asymmetric shape of continuously varying curvature. In practice, since many shoes are sold directly to the intending wearer with the assistance of staff in shoe shops, it is necessary, and for customer and vendor alike tiresome, to need to keep in stock a variety of shoe sizes which can be tried on in the shop to see if they feel comfortable. This approach has led to a recognised problem in so far as the customer will either know, or a quick measurement will suffice to determine, the general size of their foot, and even whether their feet are relatively wide or narrow, but that this is an inadequate guide to finding one, from a range of sizes of the particular shoe design which the customer wishes to purchase, which is a comfortable fit. Very often the first attempt at finding a shoe which fits comfortably for a given customer proceeds in a series of steps where first of all the customer tries on a shoe into which a foot can be inserted, but very often that is found to be too tight for comfort and in particular that the customer needs a wider fitting. The difficulty with the standard approach to shoe sizing adopted for all sizing systems is that to have a wider fitting shoe they need to go up a size which makes the shoe longer, and while selecting from a set of shoes made to different standard sizes all to the same design, there is a tendency for the process of finding a shoe which is wide enough to be comfortable to result in a shoe which is too long for the user’s comfort, though the length of the shoe subjectively tends to have a lower influence on comfort than its width. We have now found that an improved approach is to construct the last on which the shoe is manufactured in such a way that the exterior contour of the base of the last, on two opposite sides of the base of the last, is a pair of opposite circular arcs, where the centre of the circle defining those arcs is at a distance from the heel end of the last to the position of the joint girth. This shaping of the outer edges of the last bottom renders a flexibility in the shape of the toe portion of the last to suit different types of shoe, where the distance between the ends of the lateral outer edges of the rear part of the toe portion is equal to the diameter of the circle mentioned in the preceding paragraph. The last design system according to the invention is thus based around the distance between the centre of the heel portion of the last and the centre of the ball of the foot, the point at which the joint girth is measured. The width of the foot at the position of the ball of the foot is known as the tread width. This, combined with the angle of the line between those two centres enables a more logical sizing system to be adopted which adapts not only to the regular variations in dimensions from small to large fittings, but which can also easily be adapted to apply to lasts for “flat” shoes which have a sole of relatively even thickness from front to back through to “high heeled” or “wedge” shoes where the heel of the shoe made on the last is elevated relative to the front portion of the shoe by an appropriate amount. Making lasts in accordance with the present invention enables a set of lasts to be manufactured where the correspondence between the shape of the last and the overall size avoids or minimises the problem noted above that using conventionally shaped standard lasts wider fittings tend to generate proportionally longer shoes where comfort width wise is sacrificed to inadequate matching between the size of the wearer’s foot and the length of the shoe in question. In accordance with the present invention, the last is made using, instead of the asymmetric outline of the foot, a template for the shape of the foot, the outline of which template is derived from two circles, one centred on the heel of the foot and the other on the ball of the foot. The external contour of the template has accordingly a circular shape at the heel end and two opposite circular arcuate portions on opposite sides of the foot in the region of the ball of the foot. The invention is further explained with reference to the accompanying drawings in which: Figure 1 is a diagrammatic outline view of a “size 4” (English standard sizing) foot, showing the greater joint girth and waist girth measurements of that foot; Figure 2 is a diagrammatic outline view of a “size 4” (English standard sizing) foot, showing certain measurements of that foot; Figure 3 is a line drawing showing in full lines the shape of a standard Size 4 last; Figure 4 is a diagram illustrating the construction of a template for the base of a last for a making a size 4 shoe; Figure 5 is a line drawing showing in full lines the shape of a Size 4 last made in accordance with the present invention; Figures 6 to 10 show a sequence of steps to make a last in accordance with the present invention but starting from the shape of a standard one; and In constructing lasts for a series of different sizes of shoes to be manufactured, it is customary in the shoe manufacturing to start with a particular last shape corresponding to a particular size foot and then to construct smaller and larger lasts based on the dimensions of the initially made last. The indication “size 4” on Figure 1 refers to the size of the foot in question and shows four of the six measurements of the foot which are used as a basis for making a standard fit size 4 last. These are: • the distance from the back of the heel to the ball of the foot indicated by the base line, • the toe depth, • joint girth • waist girth • seat width (the width of the underside of the foot at the centre of the heel) • tread width The dimensions shown on Figure 1 are those derived from survey measurements of a large number of women whose shoe fitting size, as determined using the standard SATRA board are “Size 4”. Figure 3 shows a standard size 4 last, diagrammatically in full lines and with dashed lines showing the outline of the lower contour of the last and the lines showing various dimensions can be seen. The waist girth and joint girth figures of 212 mm and 218mm correspond to those measured as just indicated, while the overall length of the last is variable depending on toe shape the seat width of 50 mm and the tread width of 78mm are the standard size 4 dimensions specified by SATRA. In order to make a last in accordance with the present invention, it is necessary to start by constructing a template for the base of the last. Figure 4 shows the series of steps undertaken in order to produce a template having an outer contour corresponding to that of a last in accordance with the present invention. They are as follows: Step 1 - Draw a horizontal base line 1. Y to Y Step 2 - Draw a vertical line 2 extending upwards from base line 1 and of length greater than 250mm. Step 3 - Draw a circle 3 of radius 27mm centred at a point on line 2 which is 27mm from base line 1. Step 4 - Mark a point 4 on line 2 163mm from the centre point of circle 3 and draw a circle 5 centred on point 4 and of diameter 85mm. Step 5 - Draw a straight line 6 touching circles 3 and 5 to the right as shown in Figure 4. Step 6 - Draw lines 7 and 8 parallel to line 6 and passing through the centre of circle 3 (line 7) and tangent to circle 3 (line 8). Step 7 - Draw a line of lesser or greater concavity depending on the height of the intended shoe style which is tangent to circle 5 and circle 3. These are denoted 9 and 10 on Figure 4. Step 8 - Add the desired style of toe shape, extending from the sides of circle 5 either at the level of point 4 or above point 4. On Figure 4 three alternative toe shapes are shown, and these correspond to differing overall lengths of the last in question, because the distance between the tip of the toe profile and the base line 1 depends on the chosen toe shape. This variation is shown by the dashed lines a, b and c indicated at the top of the Figure 4. Lines a, b and c are parallel to the base line 1 and the tip of the toe shape is level with the intersection of line c. Lines 6,7 and 8 are reference lines. Once the entire shape of the template has been completed by suitable smooth outlines, denoted 9 and 10 in Figure 4 respectively corresponding to the inner and outer sides of the main portion of the last and the outline of the toe shape portion, the template can be cut out and used to define the shape of the underside of a last in accordance with the invention. Figures 6 to 10 show how a template may be constructed by using an existing size 4 last. As a preliminary step, a flexible shape is made by temporarily adhering a sheet of material to the underside of an existing size 4 last, trimming the flexible material around the edges so that the base of the last is covered by a non-projecting flexible shape, peeling that shape from the base of the existing last, sticking the shape down onto a flat sheet of card and cutting the card to match the shape of the flexible shape adhered to it. Figure 6 shows a template drawn as explained with reference to Figure 4, but with the addition of a horizontal line 12 at the top, parallel to base line 1, and intersecting centre line 2 at a point distant from base line 1 by the measured length of the existing last. The card shape, denoted 12, is then placed on top of the template diagram, as shown in Figure 7, with the base of the heel and the tip of the toe on the centre line 2. As can clearly be seen in Figure 7, this shows portions of circle 5 extending both sides of the card shape 12. With the tip of the card shape kept stationary, the card shape is now pivoted around a pivot point 13 to the right as shown in Figure 8 until the circle 5 is just covered, and the contour of the card shape to the right of the toe portion then drawn on the template. The card shape 12 is then swung to the left as 5 shown in Figure 9 until the edge of circle 5 remote from the horizontal line based on point 4 is covered, and the contour of the right hand portion of the toe section then drawn onto the template, finishing up with the template as shown in Figure 10 on which appropriate girth lines 10 and 9 are shown respectively on the left and right. This template i.e. the template shown in io Figure 10, can then be used in customary fashion to define the shape of a size 4 last.

Claims

1. A template for use in making a last on which to form a shoe, the template representing the outline shape of the underside of a foot, including a heel portion, a toe portion, a maximum width portion located at the ball of the foot and a waisted intermediate portion between the maximum width portion and the heel portion, wherein a) part of the outer contour of the heel portion is a circular arc of radius one half of the seat width, andb) the outer contour of two opposite lying portions of the maximum width portion of the template are circular arcs of radius one half of the tread width.

2. A last of shape derived from the template according to claim 1 and dimensioned in the vertical plane to match the desired waist girth, joint girth and toe height of the desired shoe style.

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