Milling machines are tools used by engineers and machine creators to cut metal into a specific shape. A turret milling machine is a vertical mill, meaning the spindle — the area that performs the cuts — is positioned vertically. The turret milling machine is considered a versatile unit, because it can create a wide array of shapes. It has a quill that can be raised or lowered to create different cutting depths. Turret milling machines are only effective if they are kept at a relatively small size, because the quill is difficult to operate with larger units.
Milling machines have two primary forms: vertical and horizontal. The form describes how the spindle, or cutting unit, is positioned on the machine. All turret milling machine units have a vertical spindle that remains stationary during the entire cutting process. Only the table, the area where the metal is placed, moves.
Like a drill press, the turret milling machine has a quill unit that allows the table to move up and down. This allows the machine operator to create shallow or deep cuts in the metal to achieve different depths and create more complex machine parts. Using the quill, and by moving a part under the table called the knee, is the only way operators are able to make vertical cuts in the metal.
With other vertical mills, the table operates on a 90° angle to the spindle and the spindle remains in line with its axis. A turret milling machine uses a table that moves both perpendicular and parallel. This places more stress on the table, and the table must have more moving parts, but this also makes it easier for operators to make cuts. It also requires less pre-cutting work, because the operator will not have to take both the spindle movements and table movements into account.
Depending on the model year and brand, a turret milling machine may be automated or manual. Manual machines force operators to move the table to make accurate cuts. Automatic machines allow the operator to use formulas to tell the machine where to cut.
Turret milling machine units are typically only found in small sizes. They can be made larger, but this places more stress on the operator because the quill and knee are difficult to reach and move. With larger units, the operator would have to stop the milling whenever the milling depth is higher or lower so he or she can reach the parts and change the depth.