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LATHE OPERATIONS

LATHE OPERATIONS. The various operations that can be performed on a lathe are: Turning. Step turning. Taper turning. Thread cutting. Facing. Knurling Chamfering. Parting off . Plain turning operation. Work piece held by chuck. Plain Turning:

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LATHE OPERATIONS

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  1. LATHE OPERATIONS The various operations that can be performed on a lathe are: • Turning. • Step turning. • Taper turning. • Thread cutting. • Facing. • Knurling • Chamfering. • Parting off Dept. of Mech & Mfg. Engg.

  2. Dept. of Mech & Mfg. Engg.

  3. Plain turning operation. Work piece held by chuck Plain Turning: • The process of metal removal from the cylindrical jobs is called straight or plain turning. • Cross slide and the carriage are used to perform turning operations. • Plain turning operation is performed in two steps. • Rough turning (Roughing) • Finish turning (Finishing) Dept. of Mech & Mfg. Engg.

  4. Turning It is a process of removing excess material from the work piece to generate cone-shaped or cylindrical surface. Types: Straight turning Shoulder turning

  5. Shoulder turning (Step turning) Job having different diameters, so it forms the step from one diameter to other.

  6. Facing Tool is fed in a direction perpendicular to the lathe axis Lateral/transverse surface of job is machined. Length of tool travel = half the dia. of job Depth of cut is along the axis of job

  7. Parting off • Also know as cutting off operation, Useful in cutting away the required length from the bar stock. • Tool used is parting off tool (HSS) • Job is held in chuck & rotated at relatively high speed • Tool is fed in a direction normal to axis of rotation of job. • High feed rate is given • Abundant supply of coolant should be used

  8. Knurling • Process of embossing a diamond/ straight shaped pattern onto job. • Types: Straight , diamond & diagonal. • Indentations (knurl) provided on many outside surfaces of measuring instruments, tool etc for better grip • Special tool (knurling tool) is used for operation. • Tool consists of straight shank fitted with 1 or 2 knurling wheels (hardened steel & contains teeth on its outer surface) at its front. • Job is held in chuck and tool is fed across axis of job pressing against its surface. • In operation, tool should not be withdrawn till its complete. • 2-3 passes are required & speed should be low.

  9. Chamfering Process of beveling the extreme sharp end of job. Provided - to make the edge blunt - to enable free movement of nut on threaded job - to remove burrs

  10. Thread cutting It is operation of producing helical grooves of specific shapes on cylindrical surface. Job is held between centers/chuck/face plate & tool is held in tool post. To produce threads of pitch, P mm, the tool must travel a distance equal to P and also job must make one complete rotation. There must be definite rotary & linear motion between job & tool. This is achieved by locking/engaging the carriage with lead screw through a split half nut mechanism and gear ratio between head stock spindle and lead screw. Motion is transmitted from spindle to lead screw.

  11. Taper Turning Taper: Defined as a uniform increase or decrease in diameter of a piece of work measured along its length. Taper Turning: To produce a conical surface by gradual reduction in diameter from a cylindrical work-piece. Methods: A broad nose form tool Setting over a tail stock centre Swiveling the compound rest Taper Turning attachment Combining longitudinal & cross feed

  12. Taper Elements Total Taper = D – d Taper = (D – d)/L Taper Angle (α) [Half taper angle] Amount of taper (Conicity -K): Ratio of difference in diameter of taper to its length, K = D- d / L From, triangle – ABP or AEF, [AF = ½ of total taper & EF = L] (taper gradient) tan α = AF/EF = D-d/2L

  13. A broad nose form tool • Method is suitable only for very short tapers (max. 20mm length) • Form or broad-nose tool is used [cutting edge is ground to contain half taper angle] • During operation, lot of vibrations are caused as full cutting edge is involved in cutting

  14. Swiveling the Compound Tool Rest : Dept. of Mech & Mfg. Engg.

  15. In this method the job is rotated coaxial with lathe axis, • Compound rest is swiveled to the required taper angle and locked in position. • The carriage is also locked at that position. • To assist in swiveling at particular angle, the base of the compound rest is graduated in degrees. • For taper turning , the compound tool rest is moved linearly at an angle so that the cutting tool produces the tapered surface on the workpiece. • Limited to short tapered lengths. Dept. of Mech & Mfg. Engg.

  16. Taper angle: Angle at which the compound rest to be rotated is calculated as below. tan α = α= half taper angle D= larger diameter of the taper d =smaller diameter of the taper in mm. L= length of the taper Taper or conicity (k) = Dept. of Mech & Mfg. Engg.

  17. Taper turning by Tailstock set over method Dept. of Mech & Mfg. Engg.

  18. Setting over a tail stock centre • Principle of this method: To shift the axis of rotation of the work piece at an angle to lathe axis & feeding tool parallel to lathe axis • Method is suitable only for smaller taper angle on longer jobs • Angle at which axis of rotation of work piece is equal to half taper angle • This is obtained by sliding body of tail stock towards or away from operator by a set over screw • Amount of set over is limited and centers are not equally stressed • Required amount of set over can be calculated as follows:

  19. . Amount of off-set = Where D= larger diameter, d= smaller diameter L= length of work, l= length of taper. Dept. of Mech & Mfg. Engg.

  20. specification of a lathe. Dept. of Mech & Mfg. Engg.

  21. Specificationof a lathe • Distance between centers: • Maximumdistance that can be obtained between the lathe centers • Represents the maximum length of the work piece that can be held between centers. • Overall length of the bed: • Maximum length of the bed starting from the head stock end to tailstock end. • Swing diameter over the bed: • Largest diameter of the work piece that can be rotated without touching the bed. • Swing diameter over a gap in the bed: • Maximum diameter and the width of a work piece that can be mounted between the centers. Dept. of Mech & Mfg. Engg.

  22. Lathe classification • Bench Lathe • Speed Lathe • Engine Lathe • Tool room lathe • Capstan and Turret Lathe • CNC Lathe (automatic lathe) Dept. of Mech & Mfg. Engg.

  23. Dept. of Mech & Mfg. Engg.

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