Accuracy and quality control

Accuracy

Tolerance in textiles is the amount of acceptable variation from the specified measurement from which you can cut out pattern pieces, add components or sew seams.

curriculum-key-fact
Tolerance is measured in + or - mm.

Seam allowance is the amount of material between the edge of the fabric and the seam, and it is tested to check it meets the tolerance stated in the manufacturing specification.

Example

A factory may say that a seam allowance of 20 mm is needed, with an acceptable tolerance of +/- 5%.

5% = 20 × 0.05

= 1

The seam can have a tolerance of 1 mm either side of the 20 mm.

20 + 1 = 21 mm maximum

20 - 1 = 19 mm minimum

If this were the case, then the seam allowance could range from 19 mm to 21 mm.

Question

A factory has specified that a seam allowance of 25 mm is needed, with an acceptable tolerance of +/- 8%.

What is the possible range of tolerance?

8% = 25 × 0.08

= 2

The seam can have a tolerance of 2 mm either side of the 25 mm.

25 + 2 = 27 mm maximum

25 - 2 = 23 mm minimum

The seam allowance can range from 23 mm to 27 mm.

Quality control

During the manufacturing process, quality control (QC) checks are carried out - for example, to check whether:

  • seams are sewn straight
  • components are sewn on straight and strong
  • fabric has no faults or misprints
  • stitching is straight and neat
curriculum-key-fact
Quality control (QC) is the system of checks throughout the manufacturing process to make sure each step is completed to a high standard.

Although quality control checks can increase waste, with faulty products being thrown away, if a factory develops a reputation for being reliably high in quality, money is saved in the long term through products being reordered.

In a manufacturing flow chart, quality control checks are placed as decisions in diamonds to show where a step would need repeating if there was a mistake:

A flowchart for quality control processes within textile production. Once the pattern has been cut out, is it accurate? One the side seams have been sewn, is the stitching straight?