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Tapping Formulas

RPM = (SFM x 3.82) divided by D D = Diameter of Tap in inches
 
SFM = (3.14 x D x RPM) divided by 12 D = Diameter of Tap in inches
 
Inch Taps
Drill Size
= Major Diameter of Tap minus
.01299 x % of Full Thread
# Of Threads / inch
 
Inch Taps
% of Full Thread = Threads/in x
Major Dia. of Tap minus Drill Diameter
.01299
 
Metric Taps
Drill Siz
e = Major Diameter of Tap (mm) minus
% of Thread x Metric Pitch
76.98
 
Metric Taps
% of Full Thread =

76.980
Metric Pitch
x (Basic Major Diameter (mm) minus Drilled Hole (mm))
 
Form Tap Drill Size = Basic Tap OD
minus
.0068 x % of Threads
Threads / Inch
 
Inch Taps
IPM (For Threads)
= RPM divided by TPI (Threads per Inch)
 
Inch Taps
IPR (For Threads)
= 1 divided by TPI
 
Inch Taps
IPM (Inches Per Minute)
= IPR x RPM
 
Inch Taps
IPR (Inches Per Rev.)
= IPM divided by RPM
 
Metric Taps
MM/Min
= RPM x Metric Pitch
 
Inch Taps
In/Min
= RPM divided by # of Threads / in.
 
Distance = Rate x Time
 
Time =
Distance
Rate