Multi-Point Cutting:

 Various practical cutting operations belong to the category of multi-point machining. But, the discussion given below is limited to drilling only.

Drilling

Drilling operation is effected by a number of cutting variables which influence the procedure performance in terms of material removal rate, machined surface quality and power requirements. These variables are such as feed rate, cutting speed, drill size, and width of undeformed chip. Throughout drilling operation, axial thrust and torque are governed by workpiece properties (composition and hardness), cutting fluid efficiency, feed rate, cutting speed, drill diameter, drill geometry (helix angle and point angle, 2 φ),  drilling depth and drill wear.

Drilling of materials having different hardness (BHN) or tensile strength requires different power because the resistance to cutting varies according to the material properties. Power requirements also varies with drill diameter and/or feed rate which vary axial thrust and torque because chip cross-sectional area changes by changing these variables. Use of an appropriate cutting fluid leads to a reduction in the axial thrust (feed force) and the torque as compared to the dry drilling. Whereas drilling at big depths, supply of the cutting fluid to the drill point and chip ejection become complex. At the same time, axial thrust, torque and heat generation are reduced. Enhanced flank wear of the drill increases thrust force and torque both. Initial increase in cutting speed increases thrust force and torques both, but further increase in the cutting speed decreases them.