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Machining formulas and definitions
Machining formulas and definitionsexpand_more
Machining formulas and definitions
Machining formulas and definitionsexpand_more

Drilling formulas and definitions

To know how to calculate drilling speeds and feeds is critical for successful drilling. In this section you find the drilling formulas and definitions needed for your drilling operations, such as cutting speed, feed per revolution and specific cutting force.

Cutting speed, (vc) m/min

𝑣𝑐=𝐷𝑐⋅𝜋⋅𝑛1000

Cutting speed, (vc) ft/min

\[ v_c = \frac{D_c \cdot \pi \cdot n}{12} \]

Spindle speed,(n)rpm

\[ n = \frac{v_c \cdot 1000}{\pi \cdot D_c} \]

Spindle speed,(n)rpm

\[ n = \frac{v_c \cdot 12}{\pi \cdot D_c} \]

Penetration rate, (vf) mm/min

\[ v_f = f_n \cdot n \]

Penetration rate, (vf) inch/min

\[ v_f = f_n \cdot n \]

Feed per revolution, (fn) mm/rev

\[ f_n = \frac{v_f}{n} \]

Feed per revolution, (fn) inch/rev

\[ f_n = \frac{v_f}{n} \]

Metal removal rate, (Q) cm3/min

\[ Q = \frac{D_c \cdot f_n \cdot v_c}{4} \]

Metal removal rate, (Q) inch3/min

\[ Q = D_c \cdot f_n \cdot v_c \cdot 3 \]

Net power, (Pc) kW

\[ P_c = \frac{f_n \cdot v_c \cdot D_c \cdot k_c}{240 \cdot 10^3} \]

Net power, (Pc) HP

\[ P_c = \frac{f_n \cdot v_c \cdot D_c \cdot k_c}{132 \cdot 10^3} \]

Torque, lbf Nm

\[ M_c = \frac{P_c \cdot 30 \cdot 10^3}{\pi \cdot n} \]

Torque, lbf ft

\[ M_c = \frac{P_c \cdot 16501}{\pi \cdot n} \]

Specific cutting force, (kc) N/mm

\[ k_c = k_{c1} \cdot (f_z \cdot \sin \kappa_r)^{m_c} \cdot \left(1 - \frac{\gamma_0}{100}\right) \]

Specific cutting force, (kc) ibf/inch

\[ k_c = k_{c1} \cdot (f_z \cdot \sin \kappa_r)^{m_c} \cdot \left(1 - \frac{\gamma_0}{100}\right) \]

Feed force, (Ff) N

\[ F_f \approx 0.5 \cdot k_c \cdot \frac{D_c}{2} \cdot f_n \cdot \sin \kappa_r \]

Feed force, (Ff) ft/min

\[ F_f \approx 0.5 \cdot k_c \cdot \frac{D_c}{2} \cdot f_n \cdot \sin \kappa_r \]

Machining time, (Tc) min

\[ T_c = \frac{l_m}{v_f} \]

Machining time, (Tc) min

\[ T_c = \frac{l_m}{v_f} \]


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Drilling definitions

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Penetration rate

Productivity in drilling is strongly related to the penetration rate,vf.

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Cutting speed for indexable drills

– one central and one peripheral insert

The cutting speed declines from 100% at the periphery to zero at centre. The central insert operates from cutting speed zero to approximately 50% of vc max, The peripheral insert works from 50% of vc max. up to 100% of vc max.

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Cutting speed for solid carbide drills and exchangeable tip drills

Two edges from the centre to the periphery.

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Back taper

A solid or brazed carbide drill is ground slightly tapered on its outer diameter supply clearance, which prevents the drill from jamming in the hole.

080266.jpg

Hole depth

Hole depth (LU) determines the choice of tool. Maximum hole depth is a function of hole diameter DC and hole depth (LU).

All drilling tools

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Unsure which tool to choose?

View our selection of recommended tools and cutting data chevron_right

Want to learn more about the metal cutting basics?

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How to calculate tool life

Tool life (TL) can be measured using distance, in meters, number of holes, or in minutes.

Tool life calculation - theoretical example:

Dc 20 mm, vc = 200 m/min, n = 3184 rpm, fn = 0.20 mm/r, hole depth = 50 mm
TL (meters): 15 meters ( 15 meters is an example. This number can be anything )
TL (No. of holes): 15 x 1000/50 = 300 holes
TL (min): 15 x 1000/vf = 15 x 1000/(fn x n)
= 15 x 1000 / (0.20 x 3184) = 23 min

The most common tool life criteria in drilling is flank wear. Tool life is dependent on:

  • Cutting data
  • Carbide grade and insert geometry
  • Workpiece material
  • Diameter (a small diameter drill travels a longer distance in a shorter time)
  • Hole depths (many short holes means many entries/exits which decrease tool life).
  • Stability

To estimate tool life and machining time, use CoroPlus Tool Guide and enter the values for your operation.

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