1 The Bourdon tube is the most important part of the instrument. The tube may be made from solid bar stock by drilling the length to the desired inside diameter and turning the outside diameter on a lathe to achieve the appropriate wall thickness. However, most general purpose gauges utilize preformed tubing purchased from a metals supplier. The gauge builder specifies the desired wall thickness, material, configuration, and diameter. The supplier provides the material in 10- to 12-foot (3- to 3.65-meter) lengths, ready for production.

2 Most manufacturers have closely guarded proprietary rolling methods for rolling the tubing into the "C" shape. The "C" shape of the tube is generally formed in an automatic rolling machine. This machine contains two precision, powered rollers, through which the tubing passes. One roller grasps the tubing end and forms the inside radius, while the other provides outside pressure to maintain uniform contact with the tubing. Each roller contains a groove that fits around the outside of the tubing; these grooves allow the tubing to maintain its circular shape rather than being flattened. In the rolling process, a steel mandrel—a bar that guides the tubing into the rollers and helps it keep its shape—is first inserted though the free end of the tubing and positioned just before the rollers. This lubricated mandrel is of the desired interior shape of the oval. The tubing then passes over the mandrel and between the rollers. One roller contains a clip that grabs the tubing; as the roller turns, it pulls the tubing and bends it into the "C" shape.

3 The same roller that grabs and bends the tubing also contains a saw blade. As the roller continues turning after creating the bend, the saw blade on it cuts the tubing to the proper length. The tubing is then heat treated in ovens.