In mechanical engineering, especially in manufacturing, three terms namely Machine, Machine Tool and Cutting Tool are frequently used. Many persons who are relatively new in this area sometime get confused because of their inability to correctly identify boundaries of those three terms. Technical meaning of machine, machine tool and cutting tool and relationship among them are elaborated in following sections.
What is a machine?
In general, a machine is a device containing a number of parts that are assembled together in such a way that it can repeatedly perform one or more specific tasks and consequently reduces the requirement of human effort. Machines may be driven by mechanical, thermal, electrical, hydraulic, pneumatic, or even chemical power. Sometime, human power driven devices (such as bi-cycle, pen, etc.) are also considered as machine as it reduces human effort requirement; however, most people do not recognize such tool as a machine. By the by, definition of machine varies with the arena of its application.
In Mechanical Engineering discipline, Machine is an assembly of mechanisms that are clustered together to perform certain material removal operations by utilizing electrical, mechanical, hydraulic, and/or pneumatic power. The number of mechanisms exists within a machine may vary from just few to few hundreds! Accordingly size of a machine also varies. Some machines, irrespective of their size, are portable, for example, a hand drill (small machine) and a large mining crane both are portable.
What is a machine tool?
The concept of machine tool is strictly restricted within the metal-working (or machining) field. By definition, a Machine Tool is a machine having following characteristics:
- It must be power driven (human operated machines are not machine tools).
- It must be non-portable (portability irrespective of size).
- It must have sufficient value (value in terms of capability and performance, not on the basis of cost).
- It can perform more than one type of machining or metal cutting operations.
- It utilizes a cutting tool (to shear off excess materials from workpiece).
If and only if all of the above four conditions are satisfied then a Machine can be called as a Machine Tool. In fact Machine Tool is the necessary (sometime mandatory) term to designate such machines which qualify all four conditions.
What is cutting tool?
Cutting tool, also called cutter, is a wedge-shaped sharp-edged device that removes excess material by shearing while machining. Cutting tool is mounted on the machine tool using some tool holding arrangements. Each cutting tool may have one or more sharp edges, and accordingly cutting tools are classified into three groups, namely, single-point tool (turning tool, shaping tool, etc.), double-point tool (drill), and multi-point tool (milling tool, broaching tool, etc.). Material removal by machining requires relative motion between cutting tool and workpiece. The required motions are provided by the machine tool and imparted either on cutting tool or on job or on both.
Relationship among machine, machine tool and cutting tool
Machine is any device that can reduce human effort in performing a task. If that machine is power driven and non-portable and can perform one or more material removal task using a cutting tool, then it can be considered as a machine tool. So all machine tools are basically machines but nor vice versa. On the other hand, a cutting tool is a small wedge shaped device that is mounted on the machine tool to remove material from workpiece. So cutting tool actually removes material while machine tool provides necessary motions and holding arrangements.