The following formulas are used to calculate the cutting conditions, similar to the method used for metric threads. 

・Spindle Speed (n) = (Cutting Speed ×1000) ÷ (Tool Diameter × 3.14) 

・Feed Rate (F) = pitch × Spindle Speed

The tool diameter is based on the "basic dimension" and the pitch is calculated from the "number of per inch (TPI)". 
The basic dimensions are defined by standards and cannot be calculated directly from the nominal size (e.g., 1/4) like Unified threads. 
Please refer to the table of basic dimensions and pitches for tapered pipe threads.

Calculation Example: PT (Rc) 1/4-19 at a cutting speed of 5 m/min 

・Spindle Speed: (5×1000)÷ 13.158 ÷ 3.14 = 121.02 ... ⇒ 120 min^-1 
・Feed Rate: 1.3368 × 120 = 160.4... ⇒ 160mm/min 

Note: The appropriate cutting speed varies depending on the tap type and workpiece material. 
Please check the catalog for details. 

Important: Machining Depth
When using tapered taps, the machining depth is critical. 
Unlike parallel threads, the thread diameter increases the deeper the tap enters. 
The processing depth is determined by the "gauge plane position." 
Please note that even for the same nominal size, the gauge plane position differs between general-purpose and short-thread types. 

Example: Camparison of Gauge Plane Position (lg) for PT (Rc) 1/4-19
When tapping tapered pipe threads, refer to the "Gauge Plane Position (lg) " in the catalog to set the correct machining depth.
・General Purpose TPT: The gauge plane position (lg) is 21mm.
・General Purpose Short Thread S-TPT: The gauge plane position (lg) is 12.5mm.
Please note that the gauge plane position varies significantly depending on the tap type, even for the same nominal thread size.

21mm

12.5ｍｍ

Basic Dimensions and Pitches of Pipe Threads