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Technical information for Threading Technical information for Threading Special Features Thread Turning Method External Thread > External Major Diameter A thread on the external Thread The largest diameter of a screw thread Thread Inserts & Tool holder Rotation Feed Direction Helix Method Drawing No. surface of a cylinder screw or cone EX RH Counter clockwise Towards chuck Regular Right Hand External Pitch Diameter EX LH Clockwise From chuck Reversed H Major 0 <- On a straight thread, the diameter of an Right Hand Internal IN RH Counter clockwise Towards chuck Regular H Pitch 0 < imaginary cylinder, the surface of which cuts the IN LH Clockwise From chuck Reversed Q Minor © < thread forms where the width of the thread and Depth of Thread > - EX LH Counter clockwise Towards chuck Regular - groove are equal Left Hand External The distance between the crest and root EX RH Clockwise From chuck Reversed m Minor Diameter IN LH Counter clockwise Towards chuck Regular measured from normal to the axis PitchJ 7 Thread > Angle The smallest diameter of a screw thread Left Hand Internal IN RH Clockwise From chuck Reversed iHelix . Pitch Root f Angle ! Helix Angle Crest The distance between the corresponding points External RH Thread External LH Thread on adjacent thread forms measured parallel to - For a straight thread, where the lead of the thread and the pitch diameter circle circumference form the axis. This distance can be defined in millimeters or by the tpi (threads per inch), which a right angled triangle, the helix angle is the angle opposite of the lead is the reciprocal of the pitch Straight Thread Nominal Diameter A thread formed on a cylinder The diameter of which the diameter limits are Internal Thread derived by the application of deviation Taper Thread A thread on the internal surface of a cylinder or cone allowances and tolerances A thread formed on a cone Left handed thread Right handed thread The Helix Angle ( j ) Internal RH Thread Internal LH Thread Lead( L) Helix angle(i) |X Pitch diamiter ( D ) A thread which, when viewed axially, A thread which, when viewed axially, winds winds in a counter clockwise and For a straight thread, where the lead of the thread and the in a clockwise and receding direction receding direction. All left handed pitch diameter circle circumference form a right angled Threads are always right handed threads are designated LH triangle, the helix angle is the angle opposite of the lead unless they are specified Machining a Multi - start Thread A thread in which the lead is an integral multiple, greater than one, of the pitch. A multi Calculating the Helix Angle Diagram start thread permits a more rapid advance without a coarser (larger) thread form Helix Angle( J3 ) Pitch P* Pitch P* First Start Machined Second Start Machined Third Start Machined (Final , 3 Starts Thread) 0 5j 4s 3] j = 2H [tpi] =m P Feed towards the chuck / 7 2.25 Special _y Toolholders 7 / / 2.5 / D Standard /? helix angle / / / 3 / 3.5 7 7 / / / 4 Pitch \ 1.5i oL Shim H1 7 7 7 7 4.5 5 Pitch Lead Pitch Standard toolholder pocket angle angle 1 i / 7 6 7 7 9 77 1 Insert Profile Style 24 • The helix angle is calculated Pitch diameter [mm] — i= 0E 50 100 150 200 Partial Profile Full Profile Full Profile for Fine Pitches Semi Full by the following formula : Feed towards 24 the tailstock \ PXN \ 11 9 P = tan - 1 JIX D Reversed helix angle \ 7 6 / \\ 5 E -1 \ 4.5 CO \ 4 \ 1.5 ° H1 \ 3 - Helix angle () ° Shim \ 3.5 Standard toolholder angle P - Pitch(mm) pocker angle \ 3 The V partial profile insert cuts without The full profile insert will form a The full profile for Fine Pitches will The Semi profile insert will form a N - No . of starts Special Toolholders \ D - Pitch diameter (mm) 2.5 topping the outer diameter of the complete thread profile including the form a complete thread complete thread including crest Lead = P x N The dimension H 1 (cutting thread. The same insert can be used crest. For every thread pitch and The topping of the outer diameter is radius but without topping the outer for a range of different thread pitches standard, a separate insert is generated by second tooth diameter edge height ) remains ^ = - 2H =- m • The helix angle can also be found constant with every insert / which have a common thread angle required Mainly used for trapezoidal profiles shim combination * For Multi-start threads, use the lead value instead of the pitch from the diagram below