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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 Pitch Diameter Right Hand External EX RH Counter clockwise Towards chuckEX LHClockwiseFrom chuck RegularReversed H Major 0 <- On a straight thread, the diameter of anPitch 0--groove are equal Left Hand External EX LH Counter clockwise Towards chuckEX RHClockwiseFrom chuck RegularReversed m The distance between the crest and rootmeasured from normal to the axisPitchJ 7 Thread Minor Diameter>Angle Left Hand Internal IN LH Counter clockwise Towards chuck RegularIN RHClockwiseFrom chuckReversed iHelix . The smallest diameter of a screw thread Pitch RootThe distance between the corresponding pointsCreston adjacent thread forms measured parallel tofAngle! Helix Angle-For a straight thread, where the lead of the thread External RH Thread External LH Thread the axis. This distance can be defined in and the pitch diameter circle circumference form millimeters or by the tpi (threads per inch), whichis the reciprocal of the pitch a right angled triangle, the helix angle is the angleopposite of the lead Straight Thread Nominal Diameter A thread formed on a cylinder The diameter of which the diameter limits derived by the application of deviation allowances and tolerances are A thread on the Internal Thread internal surface of a cylinder or cone Taper ThreadA 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,winds in a counter clockwise andreceding direction. All left handedthreads are designated LHA thread which, when viewed axially, windsin a clockwise and receding directionThreads are always right handedunless they are specifiedFor a straight thread, where the lead of the thread and thepitch diameter circle circumference form a right angledtriangle, the helix angle is the angle opposite of the lead 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 ) First Start Machined Second Start Machined Third Start Machined (Final, 3 Starts Thread) Pitch P* Pitch P*0PFeed towardsthe chuck5j4s3]j=2H[tpi]=m/7Special Toolholders 7_y///2.252.5 D Standard/?helix angle / / / 3 / 3.5 / 7/ /7 4 PitchPitch Lead Pitch \ 1.5iStandard toolholder SohLim H1 iangle1 77/ 777pocket angle7 4.5567 77 91 Insert Profile Style 24 • The helix angle is calculated Pitch diameter [mm] —i=0E Partial Profile Full Profile Full Profile for Fine Pitches Semi Full by the following formula : Feed towardsthe tailstock 50 100 150 200\ 24 P = tan - 1 PXNJIX D Reversed/helix angle \ \ \\ 119765 E -1CO3 - Helix angle() °P- Pitch(mm)\ 1.5°Standard toolholderH1Shimanglepocker angle\\\\\ 4.543.53 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 atopping the outer diameter of thecomplete thread profile including theform a complete threadcomplete thread including crestthread. The same insert can be usedcrest. For every thread pitch andThe topping of the outer diameter isradius but without topping the outerfor a range of different thread pitchesstandard, a separate insert isgenerated by second toothdiameterwhich have a common thread anglerequiredMainly used for trapezoidal profilesN- No. of startsD-Pitch diameter(mm)Special Toolholders\2.5Lead = P x NThe dimension H1 (cuttingedge height) remains^• The helix angle can also be foundconstant with every insert /=-2H=- mfrom the diagram belowshim combination* For Multi-start threads, use the lead value instead of the pitch