How to determine the inch thread bottom hole?
Metric threaded bottom hole d=D-P.
D is the major diameter of the thread, P is the pitch
d=D-P is medium carbon and plastic materials, etc.
d=D-(1.1—1.2)P Aluminum alloy, cast iron and other soft materials
When matching, choose the method of small hole and small axis, try it yourself
Metric thread (MM thread)
Tooth depth=0.6495*tooth distance P
(Teeth angle 60 degrees)
Internal tooth diameter=
Nominal diameter-1.0825*P
M20x2.5-6H/7g (right hand)-(single thread)-(metric coarse thread)
(Nominal diameter 20mm) (tooth pitch 2.5mm)
(Internal thread fit level 6H)
(External thread fit level 7g)
Left-Double-end-M20x1.5 (Left-handed)-(Double-end thread)-(Metric fine pitch)
(Nominal diameter 20mm) (tooth pitch 1.5mm)
American thread
(Unified standard thread)
Tooth depth=
0.6495*(25.4/tooth per inch)
(Teeth angle 60 degrees)
3/4-10UNC-2A
(UNC coarse teeth) (UNF fine teeth)
(1A 2A 3A external tooth tolerance matching grade)
(1B 2B 3B internal tooth tolerance matching grade)
UNC American Unified Standard Coarse Thread
3/4 inch outside diameter, 10 teeth per inch
Outer teeth Class 2 tolerance fit
Pipe thread (English PT)
Tooth depth=
0.6403*(25.4/tooth per inch)
(Tooth angle 55 degrees)
PT 3/4-14 (taper pipe thread) taper pipe thread, taper ratio 1/16
For 3/4 inch tube, 14 teeth per inch
Pipe thread
(PS straight thread) (PF fine thread)
Tooth depth=
0.6403*(25.4/tooth per inch)
(Tooth angle 55 degrees)
PS 3/4-14 (Straight pipe thread)
PF1 1/8-16 (Straight pipe thread)
(Fine teeth)
Straight pipe thread
For 3/4 inch tube, 14 teeth per inch
For 1 1/8 inch tube, 16 teeth per inch
Pipe thread (American NPT)
(Teeth angle 60 degrees)
NPT 3/4-14 (taper pipe thread) tapered pipe thread, taper ratio 1/16
For 3/4 inch tube, 14 teeth per inch
Trapezoidal thread
(30 degrees metric)
TM40*6 nominal diameter 40mm pitch 6.0mm
Trapezoidal thread
(29 degrees ACME thread)
TW26*5 outer diameter 26mm, 5 teeth per inch
Square thread
Calculation of car teeth
Consider the conditions Calculation formula
Conversion of metric and imperial threads Number of threads per inch n = 25.4 / pitch P
Tooth pitch P = 25.4 / number of threads per inch n
Rotation speed determined by workpiece material and tool Rotation speed N = (1000 cycle speed V) / (piping rate p * diameter D)
Rotation speed determined by machine structure
The effect of the rapid movement of the tool holder Maximum turning speed of the tooth N = 4000/ P
The influence of the acceleration and deceleration of the rapid movement of the tool holder
Calculation of the lower and retract points
(Calculation of incomplete teeth) Minimum cutting distance L1
L1 = (tooth pitch P) * (spindle speed S) / 500
Maximum retract distance L2
L2 = (tooth pitch P) * (spindle speed S) / 2000
Tooth depth and bottom diameter d Tooth depth h =0.6495 * P
Tooth base diameter d = nominal outer diameter D-2 * h
Example: Car-made external teeth 3/4"-10UNC 20mm long
Conversion between metric and imperial teeth P = 25.4 / (inch thread number n)
P = 25.4 / 10 = 2.54mm
Because of the workpiece material and
Rotation speed determined by tool Outer diameter D = 3/4 inch = 25.4 * (3/4) = 19.05MM
Rotation speed N = (1000 cycle speed V) / (piping rate p * diameter D)
N = 1000V / pD = 1000 * 120 / (3.1416*19.05)
=2005 rpm (revolution/min)
Rotation speed determined by machine structure
The effect of the rapid movement of the tool holder Maximum turning speed of the tooth N = 4000 / P
N = 4000/2.54 = 1575 rpm
Comprehensive work piece material tool and mechanical structure
The determined speed N = 1575 revolutions N = 2005 revolutions
Choose the lower speed of the two, that is, 1575 rpm
The influence of the acceleration and deceleration of the rapid movement of the tool holder
Calculation of the lower and retract points
(Calculation of incomplete teeth) Minimum cutting distance L1
L1 = (tooth pitch P) * (spindle speed S) / 500
L1 = 2.54*1575/500=8.00mm
Minimum distance of retraction L2
L2 = (tooth pitch P) * (spindle speed S) / 2000
L2 = 2.54*1575/2000=2.00mm
Tooth depth and bottom diameter d Tooth depth diameter d = nominal outer diameter D-2*h =19.05-2*1.65 = 15.75mm
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