Advantages of boring mills over other machine tools
Very large parts can be easily machined using the boring mills. Any workpiece that has dimensions beyond the 60” envelope can be machined through boring mills because traditional machining centers are not equipped for large envelopes. Another advantage of the boring mill is the spindle that advances out of the headstock so that the end user is allowed to reach into the small cavities. The live spindle provides the opportunity to keep the tooling short from the cutter point to where it fixes on the spindle so that tool deflection can be minimized.
The types of boring mills
Boring mills are either Horizontal Boring Mills or vertical boring mills. The main difference between the two types of boring mills is the spindle. The spindle is mounted horizontally on the horizontal mill while on the vertical mill, it is mounted vertically. On the horizontal mill, the workpiece is stationary while the cutting tool turns while on the vertical mill, it is the cutting tool that remains stationary while the workpiece turns. The shape of the workpiece will be the factor in considering what type of boring mill will be used. However, the horizontal mill provides for more flexibility when it comes to part size. It allows for a 10 feet tall part on the table whereas in the vertical mill, part size might be limited only to about 3 feet. In spite of the differences both machines are equally popular for machine shops because of the great amount of work it does.
Important guidelines when operating boring mills
The boring mill has a spindle which extends from the anchor to the overhang. It is important to limit the overhang since the longer the spindle extends from the anchor, the greater will be the risk of deflection. Deflection will result into chatter and insert failure. An acceptable overhang is determined through a ratio of the overhang to the diameter of the bar which should be as large as possible. Ratio can be as much as 4 to 1, overhang to diameter but there are instances when the ratio can go as high as 8 to 1 without encountering problems.
The amount of horsepower that the boring mill will need can be determined through the diameter of its bar. For example, a 5-inch spindle will require from 50 to 70 horsepower. As the diameter gets larger, horsepower can be increased.
What type of insert will be used is determined whether the end results are roughing or finishing. In order to generate a sharp, clean and smooth finish, the boring tool must pass through the bore at a higher feed rate.