HNDE-COLOMBO 15 2nd year 2nd semester Subject – Production Lecturer – Mrs.A.H.F. Sattar Name Register Number M.T.N. Aher A.R.R.M. Muhamed COL/ME/2021/F/17 COL/ME/2021/F/26 "In this presentation, we will explore various lathe operations used in metalworking. We will cover screw cutting, thread classification, taper turning, drive transmission, grinding lathe tools, spring making, thread whirling, eccentric turning, and precision finishing processes. By the end of this presentation, you will have a comprehensive understanding of these essential lathe techniques." What is Screw Cutting? • • • • • • Workpiece Preparation: Choose a suitable cylindrical workpiece and mount it securely on the lathe. Tool Selection: Select the appropriate cutting tool for the desired thread profile. Tool Setup: Position the cutting tool at the correct angle and height relative to the workpiece. Thread Specification: Determine the thread pitch, depth, and profile required for the screw. Engage the Lathe: Start the lathe and bring the cutting tool into contact with the workpiece. Feed and Rotation: Gradually feed the cutting tool into the workpiece while rotating it to create the thread. Monitoring: Monitor the cutting process to ensure accuracy and adjust as needed. Completion: Continue cutting until the desired thread length is achieved. Finishing: Inspect the thread for accuracy and surface finish, and make any necessary adjustments. Finalize: Once satisfied, disengage the lathe and remove the finished screw from the machine. What is Screw Cutting? (VIDEO) Screw thread classsification Thread Form: Threads can be classified based on their shape, such as V-thread, square thread, Acme thread, and buttress thread. Thread Pitch: Threads are classified according to their pitch, which is the distance between adjacent thread crests. This includes coarse, fine, and extra-fine pitches. Thread Diameter: Threads are classified based on their major diameter, which is the largest diameter of the threaded portion. Standard sizes are typically categorized into nominal diameters. Thread Direction: Threads can be classified as right-handed (clockwise) or left-handed (counterclockwise) based on their rotational direction. Thread Fit: Threads can be classified based on the fit between mating threads, such as loose fit, clearance fit, close fit, or interference fit. Thread Series: Threads can belong to different series, such as Unified Thread Standard (UTS), Metric Thread Standard, and British Standard Whitworth (BSW), each with its own set of standardized thread forms and dimensions. Application: Threads can be classified based on their intended application, such as machine screws, bolts, nuts, pipe threads, and thread inserts. By categorizing screw threads according to these classifications, engineers and manufacturers can ensure consistency, interchangeability, and compatibility in threaded assemblies across different industries and applications. Screw thread classsification Taper Turning • • • Compound slide method Tilts the compound slide at a specific angle to create the taper. Tailstock offset method Offsets the tailstock to create the taper along the workpiece length. • Taper Turning-(VIDEO) Drive Transmission • The center lathe's drive system transmits power from the motor to the workpiece. • Key components: 1.Headstock: Houses the electric motor, spindle, and gears that rotate the workpiece. 2.Drive belt: Connects the motor to the headstock pulley. 3.Spindle: Holds and rotates the workpiece. 4.Carriage: The movable platform that holds the cutting tool. 5.Tailstock: Provides support for the opposite end of the workpiece. Diagram of Center Lathe Grinding of Lathe Tools • • 1. Aluminum oxide wheels: For general-purpose tool grinding on various materials. 2. Cubic boron nitride (CBN) wheels: For high-hardness materials like tool steel. 3. Diamond wheels: For very hard and abrasive materials. • • Selecting the Grinding Wheel: Choose a grinding wheel with the appropriate abrasive material, grit size, and hardness for the material being machined and the type of tool being ground. Preparing the Tool: Ensure the lathe tool is clean and free from any debris or previous coatings. Check for any damage or wear that may affect the grinding process. Grinding Angles: Determine the correct angles for the tool's cutting edge, clearance angle, and rake angle based on the specific tool and machining requirements. Grinding Process: Carefully position the lathe tool against the grinding wheel, ensuring proper alignment and contact. Apply consistent pressure and move the tool across the grinding wheel to shape and sharpen the cutting edges. Finishing Pass: Once the cutting edges are properly shaped and sharpened, perform a final finishing pass to remove any burrs or irregularities and achieve a smooth surface finish. Making Springs Using a Lathe • Springs can be formed on a lathe using specialized attachments or techniques. • Methods for spring making on a lathe: 1. Mandrel winding: A mandrel with the desired spring diameter is used to form the coils. 2.Live center coiling: The workpiece is rotated using a live center while the wire is fed to create the spring. 3.Thread cutting with a formed tool: A specially shaped tool cuts the spring profile directly onto the wire. Making Springs Using a Lathe-(VIDEO) Thread Whirling on the Lathe • Thread whirling is a high-speed machining process used on lathes to create threads on cylindrical workpieces. It's a faster and more efficient alternative to traditional single-point threading, particularly for mass production. • Uses a whirling tool with multiple threading inserts that rotate at high speed. • Benefits of Thread Whirling: Speed: Significantly faster than single-point threading due to the use of multiple cutting edges working simultaneously. Finish: Creates smoother and more consistent thread profiles due to the high rotation speed and multiple light cuts. Accuracy: Offers excellent dimensional accuracy and repeatability due to the precise control of the whirling head and feed mechanism. Reduced Work Hardening: The rapid chip removal and light cutting forces minimize work hardening of the material, improving thread quality. Mass Production: Ideal for high-volume production of threaded components because of its speed and consistency. Thread Whirling on the Lathe (VIDEO) Eccentric Turning • Eccentric turning is used to create parts with an off-center profile or an irregular crosssection. • Achieved by offsetting the workpiece center relative to the lathe center. • There are two main ways to achieve eccentric turning on a lathe: Eccentric Chuck: This method involves using a special chuck that allows you to adjust the center of the workpiece relative to the lathe spindle axis. Offset Tailstock: In this approach, you keep the workpiece centered in the chuck but offset the tailstock. This creates an eccentricity along the length of the workpiece. • Applications: Creating crankshafts with offset journals Machining camshafts with varying lobe profiles Producing decorative parts with non-circular cross-sections. Eccentric Turning- (VIDEO) Precision Finishing Processes After initial machining operations on a lathe, various techniques can be employed to achieve a highquality surface finish on the workpiece. Here's a breakdown of some common precision finishing processes used on a lathe: 1. Honing: Uses a honing stone, a long, slender abrasive stick, to improve the dimensional accuracy and surface finish of a workpiece. The stone is passed back and forth along the rotating workpiece, creating a smooth and precise surface. Applications: Ideal for parts requiring tight tolerances and a low surface roughness, such as hydraulic components, pistons, and bearing journals. 2. Lapping: Employs a fine abrasive compound applied to a lap, a flat tool made of cast iron or other material. The workpiece is pressed against the rotating lap, removing microscopic material irregularities to create an ultra-smooth surface finish. Applications: Used for critical components requiring extremely high surface quality, such as optical components, gauge blocks, and sealing surfaces. 3. Polishing: Removes surface imperfections and creates a reflective finish using polishing compounds and buffing wheels. Polishing focuses more on aesthetics and improving wear resistance by reducing friction. Applications: Suitable for parts requiring a bright or decorative finish, such as musical instruments, jewelry, and molds. • Choosing the Right Process: The selection of the appropriate finishing process depends on the desired outcome: Dimensional Accuracy: Honing is best for achieving precise dimensions and geometric tolerances. Surface Smoothness: Lapping creates the smoothest possible finish for critical applications. Surface Finish and Aesthetics: Polishing prioritizes a bright, reflective finish and improved wear resistance. Safety Precautions When Operating a Lathe • • Thank You!
