There are two basic types of milling machines: horizontal and vertical. In the horizontal machine, the cutting tool and spindle move in a horizontal manner. In the vertical machine, the cutting tool and spindle move up and down. Milling machines can be used to create very complex or simple parts, depending on the end need. One machine is not better than the other; they simply perform a different set of movements. Machined parts can be found in most items in use today, including dryers, toasters and ovens.
Before milling machines, filing of metal or other materials was done by hand to produce the desired part. In the early 1800s, machinists began working on a way to develop a machine that could produce the same result mechanically. Eli Whitney is credited as inventing the first milling machine. Around 1803, James Nasmyth built a milling machine, which instituted a six-way indexing fixture. Indexing refers to the motion of moving the tools to a new position quickly, with exact precision.
A vertical milling machine shapes metal into a predetermined form, from ball bearings, to airplane parts or flywheels. A vertical mill is used typically in a machine shop; however, some people work from their own garage. A vertical mill usually works with a very tight tolerance, meaning there is a very little margin of error. An operator can scrap an expensive piece of work by incorrectly indexing the machine, or by incorrectly loading the part.
A vertical mill vastly decreases the time it takes to produce a part. For example, a hand milled part might take several days to complete, whereas the same part produced on a vertical mill could take just minutes. The milling machine has decreased the labor-intensive work of machinists by allowing the machine to do the work that, at one time, was done by hand.
A vertical milling machine is considered large machinery, and not just for its massive weight, which can vary from 1500 lbs to well over 6000 lbs. Typically, a vertical mill is shipped to a location partially assembled. Assembly is completed onsite. The smaller vertical mills might be only 5.5 feet tall, while a large mill can stand well over 10 feet high, and create a footprint of 20 feet square or larger.
A vertical milling machine's spindle axis is aligned in a vertical manner to the machine's bed. That means that the cutting tool is arranged vertically to shape the metal or other material into the desired form. The vertical mill moves while the part remains stationary. The vertical mill has controlled movements, either mechanically (by hand), or through programming via a computer.
A vertical milling machine can make small parts, such as slots, or large parts, such as torque converters. Cooling fluid is often used to keep the part cool, lubricate the milling tools and the part, and wash away sludge and metal chips. The machined part can be polished in the vertical mill, giving it a chrome-like finish.
A machine operator must pay close attention to his work in order to produce quality parts. He must learn to read blueprints, so he can measure the parts to ensure they meet the required specifications. As with any machinery, it is imperative that the operator is thoroughly and properly trained on the use of the vertical mill. Leaving the guard window open while the machine is operating is potentially life-threatening. Operators should wear safety glasses at all times during the machine's operation.