Determination of diameter and depth of bottom hole before tapping and chamfering of orifice
(1) In the process of tapping, the cutting edge is mainly used to cut metal, but it also has the function of extruding metal, so the metal bulges and flows to the tooth tip. Therefore, before tapping, the drilled hole diameter (i.e. bottom hole) should be greater than the inner diameter of the thread.
The diameter of the bottom hole can be calculated according to the manual or the following empirical formula:
Brittle materials (cast iron, bronze, etc.): drill diameter d0 = D (outer diameter of thread) - 1.1p (pitch)
Plastic material (steel, copper, etc.): drill diameter d0 = D (outer diameter of thread) - P (pitch)
(2) When tapping the thread of blind hole, the depth of the hole should be greater than the length of the thread because the tap can not tap to the end.
The depth of blind hole can be calculated according to the following formula:
Depth of hole = depth of required thread + 0.7d
The diameter of common thread bottom hole can be simply calculated according to the following formula
The size to be tapped is multiplied by 0.85
For example: m3 -- 2.4mm
M4--3.1mm
M5--4.2m
M6--5.1mm
M8--6.8mm
Calculation method of metric thread:
Bottom diameter = major diameter - 1.0825 * pitch
Calculation method of inch screw thread:
Bottom diameter = major diameter - 1.28 * pitch
Brittle material drilling diameter d = D (thread diameter) - 1.1p (pitch)
Drilling diameter of plastic material d = D (outer diameter of thread) - P (pitch)
In addition to the above empirical formula, the tolerance class of thread should also be considered
Outer diameter pitch for common metric thread.
Metric thread (mm thread)
Tooth depth = 0.6495 * pitch P
(tooth angle 60 degrees)
Diameter of internal teeth=
Nominal diameter - 1.0825 * P
M20x2.5-6h / 7g (right hand) - (single thread) - (metric coarse thread)
(nominal diameter 20 mm) (pitch 2.5 mm)
(internal thread fit grade 6h)
(external thread matching grade 7G)
Left double head-m20x1.5 (left hand) - (double head thread) - (metric fine thread)
(nominal diameter 20 mm) (pitch 1.5 mm)
American screw thread
(unified standard thread)
Tooth depth = 0.6495 * (25.4 / teeth per inch)
(tooth angle 60 degrees)
3/4-10UNC-2A
(UNC coarse teeth) (UNF fine teeth)
(1a, 2a, 3A tolerance grade of external teeth)
(1b, 2b, 3b inner tooth tolerance fit grade)
United States standard coarse thread
3 / 4 inch OD, 10 teeth per inch
Class 2 tolerance fit of external teeth
Pipe thread (inch PT)
Tooth depth = 0.6403 * (25.4 / teeth per inch)
(tooth angle 55 degrees)
Pt 3 / 4-14 (taper pipe thread) taper pipe thread, taper ratio 1 / 16
3 / 4 inch, 14 teeth per inch
Pipe thread
(PS straight thread) (PF fine thread)
Tooth depth = 0.6403 * (25.4 / teeth 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
3 / 4 inch, 14 teeth per inch
1 1 / 8 inch, 16 teeth per inch
Pipe thread (US NPT)
(tooth angle 60 degrees)
NPT 3 / 4-14 (tapered pipe thread) tapered pipe thread, taper ratio 1 / 16
3 / 4 inch, 14 teeth per inch
Trapezoidal thread
(30 degrees Metric)
Tm40 * 6 nominal diameter 40mm pitch 6.0mm
Trapezoidal thread
(29 degree acme thread)
Tw26 * 5, outer diameter 26mm, 5 teeth per inch
Square thread
Calculation of turning teeth
Calculation formula of considering conditions
The number of threads per inch of conversion between metric teeth and English teeth n = 25.4/pitch p
Pitch P = 25.4 / threads per inch n
Because the rotational speed determined by the workpiece material and the tool n = (1000 cycle speed V) / (pi * diameter d)
Because the machine structure determines the speed
Influence of rapid movement of cutterbed on maximum rotation speed of turning teeth n = 4000 / P
The influence of acceleration and deceleration on the rapid movement of cutterbed
Calculation of undercut point and undercut point
Minimum cutting distance L1 (calculation of incomplete teeth)
L1 = (pitch P) * (spindle speed s) / 500
Maximum distance of tool retraction L2
L2 = (pitch P) * (spindle speed s) / 2000
Tooth depth and root diameter D tooth depth h = 0.6495 * P
D = nominal diameter D - 2 * h
Example: Turning external teeth 3 / 4 "- 10unc 20mm long
Conversion pitch between metric and English teeth P = 25.4 / (inch thread number n)
P = 25.4 / 10 = 2.54mm
Because the rotational speed determined by the workpiece material and tool, the outer diameter d = 3 / 4 inch = 25.4 * (3 / 4) = 19.05mm
Speed n = (1000 cycle speed V) / (PI p * diameter d)
N = 1000V / pD = 1000 * 120 / (3.1416*19.05)
=2005 RPM (RPM)
Because the machine structure determines the speed
Influence of rapid movement of cutterbed on maximum rotation speed of turning teeth n = 4000 / P
N = 4000/2.54 = 1575 rpm
The rotational speed determined by the combination of workpiece material, cutting tool and mechanical structure is n = 1575 rpm and N = 2005 rpm
The lower one is 1575 rpm
The influence of acceleration and deceleration on the rapid movement of cutterbed
Calculation of undercut point and undercut point
Minimum cutting distance L1 (calculation of incomplete teeth)
L1 = (pitch P) * (spindle speed s) / 500
L1 = 2.54*1575/500=8.00mm
Minimum distance of tool return L2
L2 = (pitch P) * (spindle speed s) / 2000
L2 = 2.54*1575/2000=2.00mm
Tooth depth and root diameter D tooth depth diameter d = nominal outer diameter D-2 * H = 19.05-2 * 1.65 = 15.75mm
