Friday, October 30, 2009

Shoe Lasts and Metrology

"The close relationship between a man and his shoe maker was based on the shared secret of the client's measurements. The statistics of clients were never disclosed."

Most shoes are made to a last which is a foot model with dimensions and shape similar to the anatomical foot but sufficiently different to not be exact. The last accommodates shoe manufacture and to some extent influences it’s the final fit and shoe durability.




Last
Before mass production, the original shoemaker started the shoe making process by taking a footprint outline of the sole. A block of wood (last block) was whittled or chiselled into a wooden last from the print. In the beginning a last (‘laest’, Old English meaning footprint) was made from wood but now are made in metal or plastic. These are complex structures compiled from many foot measurements. The finished lasts is not the exact size and dimensions of the anatomical foot but instead an abstract representation with specific functions. It is usually deeper in the midfoot region with a sharp 'feather edge' where the upper surface meets the sole. The last is clipped along the topline (around the ankle) and is flared over and extended in the toe region. This provides shape and applies appropriate tension when the shoe distorts to contain the loaded foot. Lasts give a working surface on which flat leather components can be given plastic form. The physical dimensions accommodate the foot during activity and the last contains contemporary fashion and styles such as toe shape. To allow the last to be removed from the shoe they are often hinged around the instep. Modern lasts are totally unlike the foot with the sole of the last, flat in order to assist in manufacture. The last is the single most important element in the shoe making process. The last is made from measurements to ensure proper size and fit of the shoe which includes tread and shoe performance. Standard measurements include girth of ball, waist, and instep for given shoe sizes relative to the type of footwear.

Anthropometry
Studies show over 90% of people have different sized feet and the individual foot has an infinite variation of morphology despite this lasts are made to match as a pair. The concept of a perfect fit is not a reality. This is further complicated by the distribution or proportions of foot mass which differ with individuals resulting in linear measurement such as length and breadth of the foot as inadequate. It is also important shoemakers consider mass and volume if an exact fit can be afforded. To ensure a best fit, measurements are taken at strategic locations and the shoemaker uses both linear as well volume measurement to construct a shoe. The modern last is made in three dimensions although it is not a direct replica of the foot. Instead it is made with production requirements, in mind. The last maker may take up to 35 measurements before the model last can be made. A shoe fitter may concentrate on length, ball width, heel, topline, arch and instep. The shoe is expected to wear well, feel well, keep its shape with wear, retain its style character, tread properly, allow for reasonable foot freedom, maintain both foot and shoe balance, remain structurally intact. These features are not always dependent on the quality of materials or components, or the manufacturing process. The design and multiple dimensions of the last provide the basis for the above.

Measurements
The majority of measurements are volume rather than the traditional length and width associated with shoe fit.





Throat opening
The distance from the vamp point to the back seam tuck.

Length
The length measurement of the foot from the back of the heel to the tip of the longest toe.

Foot Girth
There are four girth and circumference measurements taken on a last. These are the ball; waist, instep and heel (back of heel to instep). Measurement requires careful assessment of the foot, which cannot be accomplished with the same precision as linear measurements. The modern last maker uses precision instruments to determine girth but the old shoemakers used the hand span to this same effect. Aspects of the foot were measured against the shoemaker's hand; the ball of the foot was compared to the girth between the thumb and the middle finger. The instep was measured between the thumb and the little finger. This method was subject to enormous variations depending upon the size of the shoemaker's hand.

Ball girth
This is the girth measurement around the ball of the last to determine the width and volume allowance inside the shoe.

Waist girth
The girth at the waist on the last.

Instep girth
The circumference around the foot at the instep.

Heel girth
The distance around the foot from the rear base of the heel to the top of the instep.

Recede Toe



This is the part of the last, which projects beyond the tip of the toes forming the rounded contour of the front of the shoe. A tapering recede as in sharp toed shoes increases the overall length of the shoe. In a poorly designed last the recede may encroach on the toes increasing tension on the ends of the toes. This may be referred to as tight lasting.

Heel-to-ball
This dictates the position of the hinge of the forefoot (metatarsal phalangeal joints) and the widest part of the shoe (across the metatarsal heads).

Toe Spring
This describes the elevation of the under surface of the sole at the toe to give a slight rocker effect to the shoe. The amount of toe spring (built into the last) depends on the shoe style, sole thickness and heel height. This is built into the last design and compensates for the stiffness of the footwear and provided a stress free take off into propulsion. The more rigid the soling material the greater the toe spring. Many shoes will also display a slight heel spring.

Tread
This describes the width across the sole under the ball of the last and it should correspond to the dimension of the feet. The tread point on the last represents the bottom forepart just behind the ball and in contact with the base plane.

Flare



This describes the curve or contour of the last. The swing is determined by the position of the forepart when the last is bisected longitudinally forwards from the centre of the heel arc. With inflare lasts there is an inward medial swing to the forepart and most modern shoes are made on an inflare last (banana last) because it is thought shoes are more comfortable. An outflare last describes the opposite with the swing lying to the lateral side of the forepart. Sometimes used in bespoke footwear for infants with diagnosed foot development problems. Straights last describe neither an inflare or outflare preference. The long axis of the last when drawn through the bisection of the heel curve describes two equal longitudinal halves. The normal foot has a straight axis and hence straight lasted shoes can be worn on either foot. Prior to the introduction of machinery to make heeled shoes it was common to have shoe made with a straight flare until the turn of the twentieth century.

Saturday, October 24, 2009

The anatomy of the shoe

According to McPhoil (1988) the structure of a shoe can be divided into two parts: an upper and lower (or bottom part). Sections of the upper are made up of the vamp, quarter, toebox, throat, insole board, and topline. The sections of the lower shoe consist of an outsole, shank and heel.


The Upper of the Shoe
The upper of a shoe consists of all parts or sections of the shoe above the sole. These are attached by stitches or more likely moulded to become a single unit then the insole and outsole are attached. The upper of the shoe consists of the vamp (or front of the shoe), the quarters (i.e. the sides and back of the shoe), and the linings.

Uppers are made in a variety of different materials, both natural and synthetic. Leather became the obvious choice because it allowed air to pass through to and from the skin pores (breath) keep feet at a constant temperature. The plastic properties of animal skins mould shoe leather to the foot beneath. The ability for leather to crease over flexor surfaces further facilitates the function of the foot. Ironically synthetics used as uppers display elastic properties, which mean shoe uppers never quite adjusts to the foot shape in the same way as natural leather. Synthetics are cheaper to mass-produce and are now found in most footwear. Synthetic surfaces provide waterproofing and most leather today has synthetic components. An alternative shoe cover is cotton corduroy woven fabric which provide lightweight breathable surfaces.

Vamp



The vamp covers the top (dorsum) of the foot (includes the tongue piece) and superior aspects over the toes. The toe puff is reinforced and serves to give the shoe a shape as well as protect the digits. The vamp is often made of more than one piece creating a decorative pattern. There are various types of vamps suited to different styles of shoes.

Quarters
Quarters are the complete upper part of the shoe behind the vamp line covering the sides and back part of the shoe. The top edge of the sides and back of the quarter describes the topline. In athletic shoes the topline is usually padded and referred to as a collar. The medial and lateral sections join in a seam at the posterior end of the shoe. In Oxford style lacing shoes, the eyelet section is formed by the superior part of the quarter (while the underlying tongue is part of the vamp). In the Gibson style the lacing segment forms part of the vamp. The heel section of the quarter is frequently reinforced with a stiffener to help support the rearfoot. In boots the quarter is referred to as 'top'. In the bal method of construction, the front edges of both quarters are stitched together and covered with the back edge of the vamp (Rossi,2000,p8). In the Blucher bal method the quarter panels are placed on top of the vamp, and the front edges are not sewn together. In comparison with the Bal method, the Blucher bal method permits the fitting of a larger foot girth by broadening the throat of the shoe.

A convalescent shoe (open to toe) is a variation on the Blucher method in which the lacing extends to the front edge of the vamp. In athletic shoes the vamp and quarter panels are often one continuous piece of nylon or leather with additional leather pieces added to reinforce critical areas of the shoe. Reinforcement added to the region of the medial longitudinal arch are termed the saddle if it is added to the outside of the shoe or the arch bandage if it is added to the inside of the shoe.

The counter is a component of the quarter that stabilises the hindfoot in the shoe and retains the shape of the posterior portion of the shoe. Counters are usually made from fibreboard or heat moulded plastic. Foxing (Rossi 2000, p68) is an additional piece of leather that covers the counter externally. Sometimes a counter will extend medially to support the heel and prevent prolonged pronation. In some children's shoes and athletic footwear the stiffener is extended on the medial of the arch to provide an anti-pronatory wedge.

Toe cap
Many shoes incorporate a toecap into the upper of the shoe. Toecaps are either stitched over or completely replace the distal superior aspect of the vamp and can be made into a decorative features referred to as toe tips. The toe box refers to the roofed area over and around the part of the shoe that covers the toes. The function of the toe box is to retain the shape of the forefoot and allow room for the toes. The height and width of the toe box is dictated by shape of the last used to construct the shoe. Certain types of non-athletic and athletic footgear will offer extra depth in the toe box.

Linings
In quality shoes the quarters and vamps are lined to enhance comfort and durability. Linings may consist of various materials i.e. leathers, fabrics, and manmade synthetics. The lining on the insole segment is called 'the sock' and may be full-length, three-quarter or just the heel section. Many linings are made of synthetic material and are usually confined to the quarters and the insock.

Throat
The central part of the vamp just proximal to the toe box. The throat is formed by the seam joining the vamp to the quarter i.e. throatline. The position of the throat line depends on the construction of the shoe, for example a shorter vamp and longer quarters define a lower throat line. This gives a wider lower opening for the foot to enter the shoe. The throat is defined by the connection of the rear edge of the vamp and the front part of the quarter. The location of the throat will vary with the design of the shoe. Because the vamp and quarter panels are often one piece in the athletic shoe, the throat is at the eye stay. This refers to the point where the lacing is attached to the vamp. The throat of the shoe dictates the maximum girth permitted by the shoe.

The Sole of the Shoe
The term sole derives from 'solea' a Latin word meaning soil or ground.

Insole (inner sole)
A layer of material shaped to the bottom of the last and sandwiched between the outsole (and midsole) and the sole of the foot inside the shoe. The insole covers the join between the upper and the sole in most methods of construction and provides attachment for the upper, toe box linings and welting. This provides a platform upon which the foot can operate and separates the upper from the lower. The insole board is necessary in shoes that are constructed using cemented or Goodyear welt techniques because it is the attachment for upper and lower components. The majority of insole boards are made of cellulose and are treated with additives to inhibit bacterial growth. Athletic shoewear will often have a sockliner, a piece of material placed over the top of the insole board (glued in position or removable.

Outsole
This is the outer most sole of the shoe, which is directly exposed to abrasion and wear. Traditionally made from a variety of materials, the outsole is constructed in different thickness and degrees of flexibility. Ideal soling materials must be waterproof, durable and possess a coefficient of friction high enough to prevent slipping. Leather has poor gripping capabilities and synthetic polymers are much preferred. There are also an infinite variety of surface designs. Extra grip properties can be incorporated in the form of a distinctive sole pattern with well-defined ridges. Alternatively they can be moulded with cavities to reduce the weight of the sole. These cavities need to be covered with a rigid insole or can be filled with light foam to produce a more flexible sole. In some cases two or more materials of different densities can be incorporated into the sole to give a hard wearing outer surface and a softer, more flexible midsole for greater comfort. Synthetic soling materials will off the physical property of dampening down impact levels (shock attenuation).

Shank



The shank bridges between the heel breast and the ball tred. The shankpiece (Rossi 2000, p154) or shank spring can be made from wood, metal, fibreglass or plastic and consists of a piece approximately 10cm long and 1.5 cm wide. The shank spring lies within the bridge or waist of the shoe, i.e. between heel and ball corresponding to the medial and lateral arches. The shankpiece reinforces the waist of the shoe and prevents it from collapsing or distorting in wear. The contour of the shank is determined by heel height. Shoes with low heels or wedged soles do not require a shank because the torque between the rear and forefoot does not distort the shoe.

Heel
The heel is the raised component under the rear of the shoe. Heels consist of a variety of shapes, heights, and materials and are made of a series of raised platforms or a hollowed section. The part of the heel next to sole is usually shaped to fit the heel, this is called the heel seat or heel base. The heel breast describes front face of the heel. The ground contact section is called the top piece. Heels raise the rear of the shoe above the ground. A shoe without a heel or midsole wedge may be completely flat. When the heel section sits lower than the forefoot the style is called a 'negative heel' .

Welt
The strip of material which joins the upper to the sole. Most shoes will be bonded by Goodyear-welted construction. Some shoes use an imitation welt stitched around the top flat edge of the sole for decorative purposes, but it is not a functional part of the shoe.

References
McPhoil TG 1988 Footwear Physical Therapy 68:12 1857-1865.
Rossi W A (editor) (2000) The complete footwear dictionary (2ed) Kreiger Publicating Co: Florida.