Precision Machinists

Precision machinists are trained to operate most types of machine tools that shape pieces of material—usually metal—to specific dimensions. The work done by machine tools can be classified into one of the following categories: cutting, drilling, boring, turning, milling, planing, and grinding.

After receiving a job assignment, the machinist's first task is to review the blueprints or written specifications for the piece to be made. Next the machinist decides which machining operations should be used, plans their sequence, and calculates how fast to feed the metal into the machine. When this is complete, he or she sets up the machine with the proper shaping tools and marks the metal stock (a process called layout work) to indicate where cuts should be made.

Once the layout work is done, the machinist performs the necessary operations. The metal is carefully positioned on the tool, the controls are set, and the cuts are made. During the shaping operation, the machinist constantly monitors the metal feed and the machine speed. If necessary, the machinist adds coolants and lubricants to the workpiece to prevent overheating.

At times machinists produce many identical machined products using a single machine; at other times, they produce one item by working on a variety of machines. After completing machining operations, they may finish the work by hand using files and scrapers, and then assemble finished parts with hand tools.

Machinists' work requires a high degree of accuracy. Some specifications call for accuracy within .0001 of an inch. To achieve this precision, they must use precise measuring instruments.

In the past, machinists had direct control of their machines. However, the increasing use of numerically controlled machines and, in particular, computer numerically controlled machines, has changed the nature of the work. Machinists may now work alone or with tool programmers to program the machines that make the parts. They may also be responsible for checking computer programs to ensure that the machinery is running properly.

Some machinists, often called production machinists, may produce large quantities of one part. Others produce relatively small batches of parts or even one-of-a-kind items. Finally, maintenance machinists specialize in repairing machinery or making new parts for existing machinery. In repairing a broken part, the maintenance machinist might refer to existing blueprints and perform the same machining operations that were used to create the original part.