Formula for Drilling
Inch
Cutting speed (vc)
vc (SFM) : Cutting Speed
DC (inch) : Drill Diameter
π (3.14) : Pi
n (min-1) : Rotational Speed of the Main Spindle
*Unit transformation (from "mm" to "m")
(Problem)
What is the cutting speed when main axis spindle speed is 1350min-1
and drill diameter is .500inch ?
(Answer)
Substitute π=3.14, DC=.500inch, n=1350 into the formulae
vc=π×DC×n÷12=3.14×.500×1350÷12=176.6SFM
The cutting speed is 176.6SFM.
Feed of the main spindle (vf)
vf (IPM):Feed Speed of the Main Spindle (Z axis)
fr(IPR):Feed per Revolution
n(min-1) :Rotational Speed of the Main Spindle
(Problem)
What is the spindle feed (vf) when the feed per revolution is .008IPR and main axis spindle speed is 1350min-1 ?
(Answer)
Substitute fr=.008,n=1350 into the formulae
vf=fr×n=.008×1350=10.8IPM
The spindle feed is 10.8IPM.
Drilling time (Tc)
Tc (min) : Drilling Time
n (min-1) : Spindle Speed
ld (inch) : Hole Depth
fr (IPR): Feed per Revolution
i : Number of Holes
(Problem)
What is the drilling time required for drilling a 1.2inch length hole in alloy steel at a cutting speed of 165SFM and a feed .006IPR ?
(Answer)
Spindle Speed n =(165×12)÷ (.59×3.14) = 1068.8min-1
Tc=(1.2×1)÷(1068.8×.006)=.187
=.187×60≒11.2sec.
The answer is 11.2 sec.
Metric
Cutting speed (vc)

*Divide by 1,000 to change to m from mm.
vc (m/min) : Cutting Speed
DC (mm) : Drill Diameter
π (3.14) : Pi
n (min-1) : Main Axis Spindle Speed
(Problem)
What is the cutting speed when main axis spindle speed is 1350min-1
and drill diameter is 12mm ?
(Answer)
Substitute π=3.14, DC=12, n=1350 into the formula
vc=π×DC×n÷1000=3.14×12×1350=50.9m/min
The cutting speed is 50.9m/min.
Feed of the main spindle (vf)
vf(mm/min):Feed Speed of the Main Spindle (Z axis)
fr(mm/rev):Feed per Revolution
n(min-1) :Main Axis Spindle Speed
(Problem)
What is the spindle feed (vf) when the feed per revolution is 0.2mm/rev
and main axis spindle speed is 1350min-1 ?
(Answer)
Substitute fr=0.2,n=1350 into the formula
vf=fr×n=0.2×1350=270mm/min
The spindle feed is 270mm/min.
Drilling time (Tc)
Tc (min) : Drilling Time
n (min-1) : Spindle Speed
ld (mm) : Hole Depth
fr (mm/rev): Feed per Revolution
i : Number of Holes
(Problem)
What is the drilling time required for drilling a 30mm length hole in alloy steel (JIS SCM440) at a cutting speed of 50m/min and a feed 0.15mm/rev ?
(Answer)
n=(50×1000)÷(15×3.14)=1061.57min-1
Tc=(30×1)÷(1061.57×0.15)=0.188
=0.188×60≒11.3sec.