Cooklin's Garment Technology for Fashion Designers

Chapter 3

Pattern Cutting and Materials Utilisation

This chapter examines the critical influence of the garment pattern on the pivotal activities in a clothing factory. There is no doubt that pattern cutting, whether performed manually or with a CAD system, is the most important technical process in the production of clothing. Apart from effective design interpretation, the pattern cutter has a major responsibility to provide the basis for the most efficient usage of materials.

MATERIALS UTILISATION

Various research projects have established that approximately 85% of the materials purchased for garment production are in the finished garment, with the remainder for one reason or another ending up as waste. This figure is called the materials utilisation percentage and it is a crucial cost factor in the price of a garment. Materials generally comprise about 50% of the cost price of a garment with labour representing approximately 20%. So an improvement of, say, 5% in materials utilisation is worth far more than a 5% reduction in production time. Whilst the pattern cutter cannot personally prevent excess materials usage in the cutting room, there are a number of procedures which can be employed to ensure that the garment pattern makes the minimum possible demands on materials requirements. These procedures are grouped together under the heading of pattern engineering.

Pattern Engineering

The overall objectives of pattern engineering are to improve the utilisation factor of a garment pattern through prudent modifications which do not degrade the design integrity. A line has to be drawn between the enhancement of materials utilisation and the maintenance of the design objectives. If the sweep of a fully flared dress is reduced by four to five centimetres or the depth of a skirt waist band is decreased by two or three millimetres, would these modifications make any material difference to the final appearance and fit of the garment? If pattern modifications are planned, they should be considered with a large measure of common sense.

The central procedures of pattern engineering are pattern accuracy, major modifications and making-up allowances.

Pattern Accuracy

Pattern accuracy is a fundamental subject. It is said, with justification, that apart from cutting mistakes, the accuracy of a pattern cutter can be judged by the amount and size of the cuttings found on the sewing room floor. Production operators are not supposed to be cutters. If they have to remove surpluses from components because of incorrect pattern alignments or erroneous allowances, then only the pattern cutter is responsible. Apart from the wasted materials, the production operators are to some extent prevented from doing the work they are engaged to do, so this situation is a twofold loss for the company. It can be eliminated to a large extent by greater precision on the part of the pattern cutter.

Major Modifications

These modifications could include seam displacements, slight reductions in flare, splitting very large components, separate instead of extended facings, etc. Some examples are shown in Figure 3.1. These, and other similar major modifications, require a pragmatic type of flexibility from the designer and pattern cutter because, design considerations apart, every saving in materials is a potential advantage for the company.

Figure 3.1

It is worth remembering that whilst many of today's consumers are design and quality literate, they are still not clothing technicians, so a small element of “bluff” is permissible.

Making-up Allowances

This covers seam and hem allowances and facing widths. According to an American survey, seam and hem allowances can together account for approximately 5.5% of the material used for the actual garment. So it is up to the pattern cutter to ensure that all these allowances are the practical minimum possible.

Seams

The most important properties of a seam are strength and flexibility and these are determined by a number of technical factors plus the characteristics of the fabric and the width of the seam allowance. Some of the more important technical factors are examined in Chapter 8, whilst a more comprehensive treatment can be found in Tyler (2008).

The width of seam allowances is primarily decided by the characteristics of the fibre to be sewn and the type of seam being sewn. In order to establish an appropriate background for the examination of these two factors, the construction elements of the most commonly used seam will be analysed. This seam, referred to as a superimposed seam, is constructed by sewing two components together along one edge of each piece (Figure 3.2), and the seam is usually pressed open.

Figure 3.2

Over many years, the clothing industry has proved that for regularly constructed fabrics, the optimal seam margin for assembly seams is 1 cm. This width combines three important elements:

1. Transverse strength (Figure 3.3) – In this context, strength refers to the ability of the seam to withstand reasonable pressures at angles to its length without spreading open excessively.

2. Handling The width is sufficient for the presser to open the seam easily by hand when pressing it open.

3. For operator controlled seaming there has to be an adequate margin between the right hand side of the pressure foot and the edge of the seam being sewn. When using a regular presser foot this margin enables the operator to visually control seam width (Figure 3.4).

Figure 3.3

Figure 3.4

Figure 3.5

It is generally accepted that loosely constructed materials require slightly larger seam allowances than those for more tightly woven fabrics. There are no rules governing this additional allowance, but in many cases, 2 or 3 mm would be sufficient. If in doubt, it is worth testing seam strength before making a decision, because wider seam allowances are not necessarily required for every type of loosely constructed fabric if the crimp percentage is high in the yarns or the fibres give the yarns greater frictional properties. The allowances for the main type of standard seams are given here.

Edges

These are enclosed seams which are typically used for the edges of collars, lapels and flaps, etc. For profile or jig-sewing a seam width of 5 mm is used, and for operator controlled edge sewing 6 mm. In both cases, if the sewing machine also has an edge trimming action, an additional 2 mm is necessary.

Knits

Garments made from knits are nearly always assembled by overlock or safety-stitch machines and the basic seam allowance is derived from the bight of the machine to be used. The bight refers to the finished seam width produced by the machine and to this an allowance of 2 or 3 mm has to be added for edge trimming.

Lap Felled Seams

Commonly used for jeans and similarly styled garments, the seam allowance is determined by the needle gauge of the machine to be used. The needle gauge is the measurement between the centres of the two needles and the seam allowance is calculated as follows:

For example, given a needle gauge of 8 mm, the seam allowance would be:

Figure 3.6

Top Stitched Seams

The two elements which determine the sewing allowances for these seams are the width of the top stitching and the thickness of the material. For very light weight materials, the seam margin is the width of the top stitching plus 2 or 3 mm (Figure 3.7). If the edges of the seam are to be overlocked, an addition of 2 or 3 mm is necessary.

Figure 3.7

On heavy materials this method would produce a thick, stiff seam and this can be remedied by using different allowances on the two components which are to be joined and top stitched. For the top component, which is top stitched; the sewing allowance is the width of the top stitch minus 3 mm. The allowance on the under component is the top stitch width plus 3 mm. Figure 3.8 illustrates the application of these allowances and it can be seen that the resultant seam construction would be thinner and more pliable than if the two components had the same seam widths.

Figure 3.8

Other Seam Types

An enormous variety of seam constructions is used in the clothing industry and it is beyond the scope of this book to examine the allowances for all of them. Some of the allowances can be pre-determined by the apparatus employed to construct the seam, whilst others are derived from the width of a material which is to be applied to, or inserted in, a seam. It is always worth checking carefully what exactly is required and, if there is any doubt, experimentation is advisable.

Final Word on Seam Allowances

Modern sizing technology ensures that the majority of consumers can purchase garments which do not require alterations to girths except possibly, skirt and trouser waist bands. Consequently there is no real practical reason to include allowances on the pattern for increasing the girths of body garments. Wider than necessary seam allowances are sometimes used for skirts and dresses, and these seams are supposedly an indication of garment quality as perceived by the consumer. This approach is perfectly acceptable if it is company policy, as long as the company understands that these seams are an additional cost factor.

Hems

This refers to the turn-ups on the lower...