VARIATION THROUGH THE AGES

Variation has been with us since the beginning of time, and man has reacted to it in a variety of ways.

Early man dealt with variation in the raw materials he selected for tools and weapons. Modern man continues to be plagued with variation problems form raw materials to finished products.

The complexity of assembled products and the demands of the information age make the problems of variation even more pronunced. No matter what improvements are made, there will always be some level of variation.

Understanding and managing variation in people will be an important issue for the future.
If early man accepted variation as a way of live (during this early time man did not inspect to a design or specification but inspected and worked the crasfted item until it was fit for his use) today we need to control our processes.

The Egyptians were the first to use measurement to help them manage their environment to build temples and the great pyramids.

The early craftsmen were subject to extreme variation in the source and availability of raw materials. Variation in raw materials and their crude tools required skilled craftsmen to minimize variation in the final outcome of the process.

During the Middle Ages craft guilds emerged to ensure that craftmen were adequately trained to do just that. This system included the use of masters, journeymen and apprentices.

It was the job of the master to see that all under his direction were trained in appropriate techniques. The master also purchased raw materials, determined wages, regulated the production process and set quality standards.

In short, the master did his best to minimize the variation in the craft process.

The age of craftman did not require the use of specification because the craftman was in direct communication with the customer. He understood the customer's needs and it was up to him to provide a product that would match them.

The use of gages, fixtures ad other tools to deal with variation can be traced back to the work of the American armories of the 19th century.

The armories during these early years depended on a system of inspection that was very subjective. The inspector would disassemble the lock to ensure that the pieces had good workmanship. The inspector would then reassemble the lock and test for function. If the musket could fire properly, it was stamped and accepted.

The balance of the 19th century would see continued refinement in the system of inspection with gages. By the turn of the century, inspection was the system of choise to weed out unacceptable variation.

During the 1890s the bicycle industry, a precursor to the automotive industry, provided an excellent study of the eraly efforts to cope with process variation and quality control.

As the marketplace demanded more mass-produced products with interchangeable parts, industry increasingly found the need to communicate with specification and tolerances.

Specifications was used to describe the quality characteristics necessary to satisfy customers' needs and to define what was to be delivered.

While industry was suffering form these added costs during the latter part of the 19th century, innovation was under way in the design and manufacture of precision measuring equipment and work had begun on standards.

This innovation paved the way for the use of written specification and tolerances for inspection and acceptance.
The manufactured items would now be measured with precision instruments and the measured results compared to the print.

This change reduced the cost of manufacturing and ushered in the era of inspection to print.

No longer would workmen be concerned about the fit, form or function of a final piece; their job was to make it to print. It would be the job of final inspectors to sort out any products that did not meet specification.

This system of sorting out unwanted variation continues to this day.

In the 19th century, efforts to eliminate variation form the system were sometimes successful due to the semplicity of the products being manufactured. But as complex systems developed, a new theory and method for understanding variation evolved.

Walter A. Shewhart of Bell Telephone Laboratories would contribute the needed theory and methods during the early 20th century.

Shewhart used his experience at the Western Electric plant to establish control limits that had proved useful in practice.

Shewhart's control chart method provided an operational definition of the concept of common and special causes of variation. The control chart is a statistical tool used to distinguish between variation in a process due to common causes and variation due to special causes.

Since 1931, control charts have been introduced in manufacturing, assembly and other types of production processes throughout the world.

When Deming worked with Japanese managers and engineers in the early 1950s, part of his teaching included Shewhart's theory and control chart method. The Shewhart control chart became a basic tool for Japanese manufacturing and production operations.