Machihe tools are made in a great many types and sizes. The variety of machine tools today is almost unlimited.Some are small enough to be mounted on a bench. Others are so large that they require special buildings to house them. Some are rather simple, while others are very complicated in construction and their controls.

Large or small, simple or complicated, machine tools can be categorized into five major classifications, identified as the five basic techniques of shaping metal.

(1) Drilling

Drilling is the operation of producing holes in solid metal. A rotating drill called a twist drill is used. Machine tools for drilling holes are called drilling machines. There are many -types and sizes of drilling machines. These machines can perform other operations besides drilling. The workpiece is held stationary, that is, clamped in position, and as the drill rotates, it is fed into the workpiece.

(2) Turning and Boring

The engine lathe is the most common type of machine tool for turning work. Turning is the operation of cutting or removing metal from a workpiece.A cutting tool is fed into or along the work while the workpiece revolves 

Boring is the operation of enlarging or machining a hole that has been drilled or cast into the metal. Boring in a lathe is done by feeding a single-point cutting tool into the work as it revolves.

(3) Milling

Milling is the operation of removing metal by means of a rotating cutting tool, which has multiple cutting edges and is called a milling cutter

(4) Grinding

Grinding is the operation of cutting or removing metal by means of an abrasive wheel called a grinding wheel. Grinding finishes work very accurately and smoothly. When grinding round work, the workpiece revolves as it is fed against the turning wheel. When grinding flat work, the workpiece is passed back and forth under the turning wheel. The grinding process is often used for the final finishing to close dimensions of a part that has been heat-treated to make it very hard.

(5) Shaping, Planing and Slotting

These operations are done to produce or machine flat, accurate surface using signle-point cutting tools. We should understand the difference between the shaper, the planer and the slotting machine. On a shaper, the cutting tool moves back and forth over the work while the work is fed against the cutting tool 

On a planer, the work moves back and forth under the cutting tool while the cutting tool is fed into or against the workpiece

Slotting is an operation similar to the operation performed on a shaper.

A slotting machine is really a vertical shaper, the cutting tool of which moves up and down. In this case, the work is fed against the cutting tool in a straight line or in a circle, depending upon the type of work being machined. Slotters, or vertical shapers, are used principally to cut certain types of gears.

Broaches may be classed as planing machines. The broach has multiple cutting teeth. lt may be applied internally, for example, to finish a square hole; or it may be applied externally to produce a flat surface or a special shape.