Milling machines were invented in the early nineteenth century and have since become indispensable in machining workshops. These machines produce parts by metal cutting using a cutting tool: the milling cutter. But for the operations this machine performs to be of high quality, every component must be too; the milling machine bed, the cutting tool, the head, the chuck and the other parts must all meet a set of technical specifications.
Features of milling machines
Milling machines are among the most versatile machines in the workshop. They can carry out many different machining operations, and they also accept a wide range of materials: metals, wood, steel, cast iron and synthetic materials. They can also produce parts with different surfaces: concave, convex, flat, curved, toothed and so on. In addition, parts machined on a milling machine can undergo further processes such as roughing and finishing.
Milling machines can be classified in two ways: by the orientation of the tool and by the number of axes. By cutter orientation, the most common types are horizontal, vertical and universal. The horizontal milling machine uses cylindrical cutters and can perform slotting work. The vertical milling machine allows the worktable to move up and down, which permits a greater depth of cut. This type can be divided into bed-type and turret or knee-type machines. Finally, universal milling machines can be converted to vertical machines with the right attachments; their distinguishing feature is that the ram or slide can move forwards and backwards.
By number of axes, these machines can have three, four or five axes; five-axis machines are the most complex and can carry out much more precise work. Generally, the bed of a conventional milling machine can only move along the X, Y and Z axes.
Parts of a milling machine
Although there are different types of milling machine, as you have seen, they all share common elements. These include:
- Bed: the entire structure of the machine rests on it.
- Body: also called the frame, it sits on the milling machine bed.
- Knee: this part moves vertically along the ways and is attached to the machine.
- Cross slide: supports the table.
- Table: the workpiece is placed on it.
- Overarm: mounted on the frame, with arbor supports that hold the tool holder.
- Tool arbor.
- CPU: the unit that controls the machine's processes (common on CNC milling machines).
- Handwheel: allows movement along the X, Y and Z axes.
- Motor: the part that turns the milling cutter.
- Column.
- Ram.
- Crank handle.
- Spindle: moves the cutting tool vertically into position.
What is the milling machine bed?
The bed is perhaps one of the most overlooked parts of a milling machine. In general terms, the bed is a fixed structural system common to all machine tools and characterised by its rigidity. This is, in fact, one of the most sought-after qualities in a machine tool. All machine tools have a bed because deformations in the structure affect machining precision. On a machine tool, for example, the deformation of the structure must be smaller than the precision required.
A machine such as the milling machine, whatever its type or model, works at high cutting speeds to remove chips, so it needs a solid structure. The main function of the milling machine bed is to facilitate machining: parts can be machined easily with minimal vibration and, of course, without deforming, so that the result is highly precise.
Bed-type milling machines
As we have seen, all machine tools have a bed, and there is also a type of milling machine defined by this part. This is the bed-type milling machine, also known as the fixed-bed milling machine. On this machine, which is vertical, the tool-holding spindle is positioned so that the cutter can rotate about its horizontal axis while remaining perpendicular to the workpiece. On these milling machines the bed can be adjusted to handle the parts easily.
It gets its name because it is precisely the table that moves, and the operations are highly precise. The milling head of the machine moves up and down along the full length of the column; the worktable can also carry heavy loads and the cutter can perform high-precision work.