This section is from the book "The Manufacture Of Boots And Shoes: Being A Modern Treatise Of All The Processes Of Making And Manufacturing Footgear", by F. Y. Golding. Also available from Amazon: The Manufacture Of Boots And Shoes.
The Production of Sole-Shapes is a very important operation in the making of boots and shoes. It requires a knowledge of the construction and proportion of the foot, besides a considerable degree of artistic skill. Sole-shapes may be prepared for two purposes - either to fit or suit lasts already in existence, or to provide shapes to enable lasts to be made to a particular pattern. It is to the latter purpose that the remarks of this chapter will be chiefly devoted. A sole-shape should represent the sole-area of a foot, and should be so constructed that it will allow, as far as possible consistent with "fashion," a free action to the functions of the foot. The difference between a draft or outline of the foot and a sole-area impression should be well understood. A draft is taken by passing an upright pencil round the foot, and the tracing made on the paper gives the contour of the margin of the foot; but it does not convey the actual sole-area or its dimensions. A real sole-area is that which is formed by the portion of the plantar surface that comes into contact or presses upon a flat surface. To obtain the latter, an impression should be taken as well as the draft or plan. Fig. 59 gives an illustration of an impression and a draft of the foot. The line will show the margin of the foot (due allowance being made for the pencil used), and the dotted portion indicates the real sole-area. To ascertain the width of the sole, allowance must be made for extension of the foot when the full weight of the body is borne upon it. A sole-shape that may be correct for one position of the foot, may not suit others. The height of the heel affects considerably the shapes of soles.
Sole Proportions may be either longitudinal or transverse. The former will locate, and should be recorded the same way as lengths are taken, i.e. on the size-stick principle. The transverse proportions are the widths of the various located positions. The principal places of taking measurements are - the width of bottom at the joint, termed tread; the width of heel, called seat; the narrowest part of the shape, the waist; and the toe. The locations of these measurements are proportioned to the length of the sole-shape, and this numerically expressed is not identical to the expression of the location of similar positions in relation to the foot's entire length.
In an average foot, the inside joint is situated two-sevenths of the length (as measured by a size-stick) from the toe end, or, if measured from the heel, five-sevenths of the whole length from the hinder part of the foot. The seat, similarly, is distanced from the heel one-sixth of the foot's length. The waist is mid-way between the tread and seat.
These positions not only afford a place for regulating the widths, but they also indicate other important features; for instance, the tread marks relatively the line of contact of the anterior portion of the foot, which line alters its position as the heel of the foot is raised, thus enabling the fore part to be shortened pro rata as the heel is raised. The seat will mark the correct position of putting on the heel of the boot or shoe so as to give the greatest support to the posterior region of the foot. A line perpendicularly-descending from the seat should pass through the centre of the heel, and will guide the design of a heel, preventing surplus "lifting" being given, thus reducing the weight of the hinder portion of the shoe, while giving its legitimate support.
In applying these positions to a last, the additional length must be noted - say two and a half sizes are allowed over the length of the foot for the last. This will alter the position, in relation to the length of the last, of the inside joint, which would be about one-third of the distance from the toe.
In the diagram No. 60 this difference is graphically shown, where ab indicates the length of the foot measured by the size-stick. The inside joint c is situated two-sevenths of the entire length ab from the toe end a. The seat d is one-sixth of ab from the heel end b. The dotted triangle cOd is supposed to illustrate the transmitted weight of the body. The distance between a and L is the addition made over the foot's length for the last-length.
The line below, Acdb, is the proportion of the sole of the foot longitudinally related, and W is the waist position situated equally distant between C and D. Below this line another one is drawn, Tjsh, that shows the proportions of the last; and it will be noted that the inside joint of the last is located one-third of the last-length from the toe end T.
The width proportions are illustrated in Fig. 61, where T equals the bottom-width, or tread. The line at S is averaged at three-fourths of the tread, but is subject to variation due to the kind of last, sort of work, etc.
The waist W is three-fourths of the seat, but is varied according to the work, such as sewrounds, etc.
The Effect of raising the Heel of the Foot upon the marginal outline of the sole-area can be best studied by taking impressions with various height heels. The principal effects are - the change of position of the line of contact of the anterior portion of the foot, and the alteration of the line of the inside of the great toe. By "line of contact" it is understood to define the position of bearing of the fore-part of the foot, and does not necessarily mean the joint-line of the sole. In Fig. 59, which illustrates a draft and impression taken from a foot, the straight line ab indicates in the margin of the foot the straight inside form, and is one of the characteristics of the "Meyer "-shaped sole ; but here it is not intended to show the sole, but only the upper margin or border of the foot. A foot may have a straight form or shape in this portion, and yet in the sole-area the line connecting the inside joint with the toe may incline inwards from the line ab, Fig. 59. To make this clear, Fig. 62 is given, showing the sole-impression without the draft or plan, where it will be observed the line ce makes an angle with the line ab. This will give an explanation to the fact observed when sole-shapes are designed upon the Meyer principle, that, after wearing, the inside corner of the toe of the boot does not fit the toe as it is supposed to do. It also gives a reason why shoes that are designed with the inside of the fore part tapering slightly away from the line ab, Fig. 62, are comfortable, and do not cause the foot to be misplaced. It must be understood, however, that in the latter fact alluded to, it is supposed that the margin of the last made to the sole-shape recedes from the feather of the last towards the line ab, Fig. 62. The line ed in Fig. 62 illustrates the line of contact for a foot with no heel.
If a block, say half-inch, is placed under the heel of the foot, the line of contact will move forwards, and it is found by experiment that it amounts to an average of 1/18 in. for each 1/2 in. that the foot is raised.
A reference should now be made to the plantar view of the skeleton of the foot, p. 29, where the phalange of the great toe has a dotted line round it.
If the foot is put upon a level surface without any heel, and the great toe be raised, it will be observed that as the toe is elevated it moves towards the middle line of the foot XY in the skeleton. The same effect is observed if the heel is raised when the foot is upon the ground, and it may be reduced to a proportion for the amount raised.
Fig. 63 is given to illustrate this ; the line Ec showing the amount the toe has travelled away from the line AB. For each 1/2 in. the heel of the foot is raised, the distance away from A is 1/9 in.