Lathe Machine Parts

• Metals are cut to shape using different machine tools in machine shops.
• A lathe cuts and shapes metal by revolving work against a cutting tool.
• Work is clamped in a chuck on the lathe spindle, or between centers.
• The cutting tool is secured in a tool post on a movable carriage.
• The cutting tool can be fed lengthwise or crosswise onto the work.
• When turning, the chuck rotates counter-clockwise when viewed from the tail stock end.

Principal Parts of a Lathe

• A center lathe has main parts that are designed to hold work pieces.

Bed

• The bed is a strong, rigid and essential part of the lathe.
• It carries all machine parts, resists cutting forces, and guides the carriage and tail stock.
• Beds are typically made of cast iron.

Head Stock

• Contains gears or a cone pulley for speed/feed adjustments.
• It contains the main spindle, which holds and rotates the work.

Tail Stock

• The tail stock supports the right-hand end of long work pieces.
• It can be clamped at any bed position.
• The tail stock spindle possesses an internal Morse taper that accepts the dead center.
• Drills, reamers, and taps can be fitted into the spindle for operations.

Carriage / Saddle

• The carriage or saddle controls the cutting tool's movement.
• It includes longitudinal and cross slides plus a compound slide and apron.
• The cross slide allows movement across the bed, perpendicular to the spindle's axis.
• This movement is used for facing and adjusting depth during turning.
• The apron is bolted to the saddle and incorporates controls for the longitudinal and cross slides.

Compound Rest

• The compound rest supports the tool post and can be swiveled on the cross slide to turn short tapers at different angles.

Tool Post

• The tool post secures the tool holder or the cutting tool, adjustable to any working position.

Lead Screw

• A long, threaded shaft positioned in front of the carriage running from head to tail stock.
• Driven from the spindle, it controls the tool's movement for automatic feed or thread cutting.

Centers

• Lathes have two types of centers; dead and live.
• The dead center sits in the tail stock spindle while the live center is in the head-stock spindle.
• When turning between centers, the dead center remains fixed while the live center rotates with the work.

Three Jaw Chuck

• The three jaw chuck is a self-centering work-holding device with three jaws that open and close with respect to the spindle center
• Three jaw chucks are used for holding regular objects like round bars and hexagonal rods.

Face Plate

• Used for turning operations, especially for holding work pieces that cannot be held in chucks.
• Different accessories are used with face plates.

Lathe Dogs and Driving Plate

• Used to drive work pieces held between centers.
• The jaws receive and clamp the work piece, with the dog tail carried by a pin in the driving plate.

Measuring Instruments

• Calipers are used to measure dimensions using steel rules.
• Vernier calipers measure accurately both outside and inside dimensions.

Micrometers

• Micrometers are used for measuring components for greater accuracy

Cutting Parameters

• Cutting speed is the speed at which material is removed, in meters per minute.
• Cutting speed relies on workpiece material, feed, depth of cut, operation type, Spindle speed (RPM) = cutting speed x 1000 / (πD) Where D is the work piece diameter in mm.
• Feed is the distance the tool traverses along the bed per work revolution, based on cut depth and desired surface finish.
• Depth of cut determines movement from the workpiece surface perpendicular to the lathe axis, depending on the operation.

Tool Materials

• Hand cutting tools are made from carbon or tool steel.
• Single point lathe cutting tools are made from high speed steel (HSS), containing 18% tungsten, 4% chromium, and 1% vanadium.
• For better heat resistance, 5-10% cobalt is added to HSS.
• Carbide-tipped tools are typically used in production shops.

Tool Geometry

• A single point cutting tool used on a lathe is a simple wedge.

Lathe Operations

Turning

• Turning produces cylindrical shapes by removing material with a traversing tool from the surface of a rotating work piece. For internal turning internal surfaces are machined in a boring operation, which enlarges a drilled hole.
• For long work, it should be faced, center drilled and supported at one end before being supported by the tail-stock.

Boring

• Boring enlarges a hole, usually done because the correct drill size is not available.

Facing

• Facing creates a flat end surface perpendicular to the axis of rotation.
• The work piece is held in a chuck, rotated, and faced by feeding a cutting tool toward the end of the work piece and perpendicular to the axis of the lathe.

Taper Turning

• A Taper is defined as the uniform change in the diameter of a work piece, measured along its length expressed as the ratio of the difference in diameters to the length.
• Short steep tapers can be made on a lathe by swiveling the compound rest, where the cutting tool is fed with the compound slide feed handle while the work piece rotates in a chuck, face plate, or between centers.

Drilling

• Drilling axially aligns holes in cylindrical parts using a twist drill.
• The work piece rotates in a chuck/face plate, and the drill bit fitted into the tail stock spindle through a chuck.
• The tail stock moves and clamps near the work; while the job rotates, the drill bit feeds into the work using the tail stock hand wheel.

Knurling

• A pattern is embossed on a work piece using a knurling tool.
• The tool presses rollers against the work to create a gripping surface for hand operation.

Chamfering

• Chamfering bevels the extreme end of a work piece for look, to enable nuts to pass freely on threaded parts or to remove damage.

Threading

• Threading cuts helical grooves on a work piece, either internal or external.
• A thread cutting tool is traversed at a specific rate, proportional to the work's revolution speed.

Safety Precautions

• Wear eye protection to prevent hot, sharp metal chips from causing damage.
• Wear short sleeve shirts to avoid loose sleeves catching on rotating parts.
• Wear work shows to protect your feet at the shop floor.
• Remove jewelry and tie back long hair to prevent entanglement.
• Always double check that work is clamped securely before starting the lathe at a low sped.
• After use, remove the chuck key from the chuck immediately.
• Avoid contact of fingers or hands with rotation axes and cutting tools.
• Avoid reaching over spinning chuck to prevent accidents if clothes or materials catch.
• Never use files with a bare tang.

Facing and plain turning

• The aim is to obtain a required diameter of a cylindrical work piece with the given length including tools and equipment such as a lathe, mild steel bar, cutting tool, box/tool post key, chuck key, and calipers.
• Facing finishes the work piece ends to make them flat, smooth, and of required length.
• Rough turning removes stock when surface finish is not critical, using deep cuts with coarse feed.
• During rough machining, there is minimal oversize dimension.

Procedure

• Secure the work piece in the lathe's 3-jaw chuck with a chuck key.
• Secure the right-hand cutting tool with a box key.
• After switching on the machine, swivel the tool post and adjust the cutting point for facing; feed the tool and move the tool post and provide movement by rotating the cross slide's hand wheel
• Once facing is done, swivel the tool post, making the cutting point parallel to the work piece's axis.
• Provide the depth by moving the cross slide and turning the tool post and side hand wheel, rotating to a longitudinal movement for length.
• Inspect the achieved dimensions using either a steel rule, an outside caliper, or a vernier caliper.

Precautions

• Always hold work pieces firmly and avoid over-feeding the tool in rough turning.
• Reduce tool overhang to prevent chatter and rough surfaces.
• Ensure the performance of facing operations runs from center to edge of the part being worked on.