Trunnion machining is a type of rotary transfer machining whose plane of motion resembles that of a Ferris wheel. In a trunnion machine tool, the trunnion is the horizontal shaft around which the workholding table, in a vertical plane, indexes parts from one machining station to the next.

Now that I’ve defined a trunnion machine, you may be asking yourself why this machine is useful compared with dial-type rotary transfer machines. Good question. Some of the advantages of vertical indexing include chip control: Trunnion machines can rely on gravity to do much of the work of getting chips out of the way of the cut. Also, trunnion configuration permits easy access to three different faces of the part. At a given station, CNC axes can reach a radial face and two axial faces. Another benefit is the amount of floor space that this machine occupies. Because most of the space needed for it is vertical, its footprint is small compared with what a group of standard machine tools would require. Also, a trunnion-type system helps the manufacturer hold tight tolerances by reducing part handling: A single chucking carries the part to every station. If the feature held in the chuck doesn’t have to be machined, then the single chucking is enough to machine the part complete.

In most industries, any shop engaged in high-volume parts production is a good candidate for trunnion machining technology. However, according to “Trunnion Trends,” most shops that find success using this machine tool are adamant about growing their manufacturing niche and are looking for a better way to produce a high parts volume. Rotary transfer is an application-focused production system, which may not be for everyone. For more information about trunnion machines, read “Trunnion Machines in Transition.”