Conventional machining operation utilizes a wedge shaped cutting tool having one or more sharp cutting edges to facilitate shearing. To achieve material removal, three relative motions between workpiece and cutting tool are indispensably necessary. One of such three relative motions is cutting velocity, other two being feed motion and depth of cut. In few cases, the cutting velocity is imparted by rotating either workpiece or cutter. Such rotation of either workpiece or cutter can be expressed in two different ways, namely cutting speed and cutting velocity.
Cutting speed is basically the rotational speed of either workpiece or cutting tool (based on the operation). It is measured by the unit—revolution per minute (rpm) and usually designated by N. On the other hand, cutting velocity is the tangential velocity of either rotating workpiece or rotating cutting tool. It is measured by the unit—meters per minute (m/min) and designated by Vc.
However, there exist few machining operations where neither workpiece nor cutting tool rotates; instead, they undergo linear motions. For example you may consider shaping or planing operation. For such cases, this linear velocity of workpiece or cutting tool is termed as cutting velocity. Cutting speed becomes invalid here, as there is no rotation. Various similarities and differences between cutting speed and cutting velocity are explained in the following passages.
Similarities between cutting speed and cutting velocity
- Both cutting speed and cutting velocity are interrelated and one is proportional to another.
- One can easily be converted to another, provided diameter of either cutter or workpiece (the rotating one) is known.
Differences between cutting speed and cutting velocity
|Cutting Speed||Cutting Velocity|
|Cutting speed is nothing but the rotational speed of either workpiece or cutting tool.||Cutting velocity is the tangential velocity of either rotating workpiece or rotating cutting tool.|
|It is expressed in revolution per minute (rpm).||It is expressed in meters per minute (m/min).|
|It is a scalar quantity.||It is vector quantity.|
|Cutting speed is associated with only those machining operations where either workpiece or cutting tool rotates.||Cutting velocity is associated with all conventional machining operations irrespective of presence or absence of rotation of workpiece or cutting tool.|
|It is usually not considered as a cutting parameter.||It is considered as one of the cutting parameters for conventional machining.|
|Cutting speed is mainly useful while operating machines including conventional one and CNC based machine tools.||Cutting velocity is useful in various analysis, such as assessment of cutting force, temperature, vibration, machinability, economy of machining, etc.|