Roll Form Tap Drill Sizes Calculator was developed to calculate recommended roll form tap drill sizes for Unified threads. Calculations are done according to formulas and charts which are given in the Machinery's Handbook. Desired thread size and % of full thread shall be specified in "Input Parameters" table of the calculator.
Roll tapping is a process which forms a thread in the hole by displacement of the material into the desired size and pitch. Roll tapping eliminates the problem of chip disposal. The threads produced with roll tapping are stronger than cut threads because the grains are continuous and unbroken, and the displaced metal is work hardened.
Roll tapping is a method to be applied to relatively ductile metals such as low-carbon steel, leaded steels, austenitic stainless steels, wrought aluminum, magnesium, copper, and ductile copper alloys.
For roll tapping, cutting tap drill sizes should not be used. Roll tapping
displaces metal from the hole walls to form the threads so cutting tap drill
leaves to much material in the hole.
Note: For more information on roll tap drill sizes for Unified screw threads including selection of taps, method of tapping, tap drill sizes for threads of American National Form and cold form tapping, please refer to pages 2015 – 2037 of
Machinery's Handbook, 29th.
Drill bit: A cutting tool used in drilling machines to drill a hole.
Unified Screw Thread: A thread
form used by the United Kingdom, Canada, and the United States to obtain screw
thread interchangeability among these three nations. It has 60° thread angle and
dimensions are stated in inch units.
UN form screw threads: The UN
thread is intended for general purpose fastening operations.
UNC (Unified National Coarse):
Most commonly used type for general engineering applications. This thread form
is used in materials with low tensile strength which makes threads more
resistance against stripping (internal threads) .UNC give possibility for quick assembly.
UNF (Unified National Fine): External
threads of this Fine Series have greater tensile stress area than comparable sizes of the Coarse series. The Fine series is suitable when the resistance to stripping of both external
and mating internal threads equals or exceeds the tensile load carrying capacity of the
externally threaded member. It is also used where the length of engagement
is short, where a smaller lead angle is desired, where the wall thickness demands a fine
pitch, or where finer adjustment is needed.
UNEF (Unified National Extra Fine):
Used when finer
pitches than UNF are needed (Ex: Short engagement length).
Tap: A mechanical tool used to make a standard thread through a hole. Different type of taps exist such as straight
fluted taps, spiral pointed taps, spiral pointed only taps, spiral fluted taps, fast spiral fluted
taps, thread forming taps, pulley taps, nut taps, and pipe taps.
Tap drill size: The required
diameter of hole before the tapping operation of the hole.
Thread class: A classification system to classify the threads for
interchangeability and manufacturability. Class 1 threads are loosely fitting
thread and used for ease of assembly. Most commonly used class is 2 and this
class is designed for general use. Class 3 is used for closer tolerances.