Lathe Operations and Functions

Lathe Machine

• A lathe is a machine used in metalworking to shape and size metal pieces.
• It operates by rotating the workpiece and using a fixed cutting tool.
• The cutting tool removes material from the workpiece, forming it to the desired shape.
• The lathe is often called the "mother/father of the entire tool family."

Inventor of Centre Lathe

• Henry Maudsley was born on a farm near Gigghleswick, North Yorkshire.
• He studied at University College London and excelled, winning ten gold medals.
• He graduated with an M.D. degree in 1857.

Function of Lathe

• The function of a lathe is to remove excess material in the form of chips.
• This is achieved by rotating the workpiece against a stationary cutting tool.

Industrial Revolution Demanded

• The industrial revolution led to a demand for:
  • Increased production
  • Higher precision
  • Changes in manufacturing processes
  • Development of high-speed lathes
  • Development of special purpose lathes

Main Parts of Centre Lathe

• Bed: A base supporting all major components
• Headstock: Holds the workpiece and supplies power
• Tailstock: Supports the other end of the workpiece
• Carriage: Slides along the ways and includes the cross slide, tool post, and apron

Lathe Components (Detailed)

• Bed: Supports all major components
• Carriage: Slides along ways; includes cross slide, tool post, apron.
• Headstock: Holds work piece jaws, provides power and various drive speeds
• Tailstock: Supports other end of the workpiece
• Feed rod & Lead screw: Rod is powered by gears from headstock

Working Principle of Lathe

• The workpiece is held between two centers or a chuck/faceplate.
• The cutting tool is fed against the revolving workpiece.
• Tool movement can be parallel to the workpiece axis for cylindrical surfaces, or inclined for tapers.

Lathe Operations

• Turning: Removes material from the outside diameter to create a finished surface.
• Facing: Produces a flat surface at the end of the workpiece or for making face grooves.
• Boring: Enlarges a hole or cylindrical cavity or creates circular internal grooves.
• Drilling: Creates a hole in the workpiece.
• Reaming: Finishes a previously drilled hole.
• Threading: Produces external or internal threads on the workpiece.
• Knurling: Creates a textured surface for decorative or functional purposes.
• Grooving: Creates a groove in the workpiece.
• Parting: Cuts the workpiece into two pieces.
• Chamfering: Bevels sharp machined edges.

Specifications of Lathe

• Height of centers
• Bed type (straight, semi-gap, or gap)
• Center distance
• Swing over bed
• Swing over cross slide
• Swing in gap
• Gap in front of face plate
• Spindle speeds range
• Spindle nose
• Spindle bore
• Taper nose
• Metric thread pitches
• Lead screw pitch
• Longitudinal feeds
• Cross feeds
• Cross slide travel
• Top slide travel
• Tool section
• Tailstock sleeve travel
• Taper in sleeve bore
• Motor horsepower and RPM
• Shipping dimensions (length x width x height x weight)

Types of Lathes

• Engine lathe/center lathe: Most common, widely used in workshops, variable spindle speed.
• Bench lathe: Smaller, mounted on a workbench; used for small precision jobs.
• Speed lathe: High-speed headstock spindle; used in wood turning, metal spinning, and related operations.
• Tool room lathe: Similar to engine lathes but designed for accuracy; used in manufacturing precision components like tools, dies, and jigs.
• Special-purpose lathes:
  • Gap lathes
  • Instrument lathes
  • Facing lathes
  • Flow turning lathes
  • Heavy-duty lathes
• Automatic lathe: Workpiece is automatically fed and removed without operator intervention; requires minimal attention post-setup.
• Turret lathe: Tailstock replaced by a turret slide; can hold multiple tools simultaneously.
• Capstan lathe: Similar to a turret lathe, but the turret moves on an auxiliary slide; used for fast production of small parts.

Operating Conditions

• Cutting speed
• Depth of cut
• Machined surface
• Chip
• Feed

Work Holding Devices

• Three-jaw universal chucks: Holds round and hexagonal work quickly and accurately
• Four-jaw independent chucks: For holding round, square, hexagonal, and irregularly-shaped parts; jaws adjustable independently.
• Collet chucks: Used for holding small workpieces, high accuracy.
• Face plates: Hold parts with irregular shapes.
• Lathe centers: Provide bearing surfaces for workpieces between centers; typically steel with carbide tips and adjusted for lubrication.
• Mandrels: Used with fixed centers to hold work pieces and support during finishing of cylindrical parts.

Headstock Spindles

• Universal and independent chuck fitted to three types of headstock spindles
  • Threaded spindle nose: Screws on, clockwise direction
  • Tapered spindle nose: Held by lock nut.
  • Cam-lock spindle nose: Held by tightening cam locks using T-wrench.

Collet Chuck

• Most accurate chuck
• Used for high-precision work
• Spring collets hold round, square, or hexagon-shaped workpieces
• Each collet has a limited range of allowable size

Types of Lathe Dogs

• Standard bent-tail lathe dog; most common, used for round workpieces.
• Straight-tail lathe dog; used for precision turning
• Safety clamp lathe dog; used to hold various work types.
• Clamp lathe dog; wider ranges and used for all shapes.

Tool Holders

• Left-hand offset toolholder
• Right-hand offset toolholder
• Straight toolholder: General-purpose use

Semi-Automatic Lathes

• Designed for short, continuous runs; human involvement for certain operations
• Capstan and turret lathes can become semi-automatic with added attachments.
• Vide range of jobs can be accommodated; higher production rates.

Turret Lathe

• Performs multiple cutting operations on the same workpiece
• Several cutting tools are mounted in a hexagonal turret.
• Tools can be quickly changed.
• Ram and saddle types with separate bases (on saddle) or more heavily constructed saddle turret machines are used for large workpieces.

Capstan Lathe

• Similar to a turret lathe
• Turret moves on an auxiliary slide
• Used for high-volume production of small parts.

Automatic Lathes

• Parts are fed and removed, automatically.
• May have single or multiple spindles
• Uses servo motor
• Limited variety and sizes.
• Manual machine controls are replaced.
• Minimum man power utilized; meant for mass production; eliminating skilled labour

Automatic Lathe Features

• Minimum man power utilized.
• Meant for mass production.
• Manual machine controls replaced by varied mechanism.
• Mechanisms for prescribed frequency of parts fed, loaded, and unloaded.
• May have single or multiple spindles.
• Tool set up may be permanent.
• May have horizontal or vertical spindles.
• More accuracy can be obtained.

Advantages of Automatic Lathes

• Greater production.
• More economical floor space.
• Improved accuracy.
• Reduced floor maintenance and inventory.
• More consistent accurate work than turret lathes.
• More constant flow of production.
• Reduced scrap loss from the reduction in operator errors.
• Operator free to work on other machines or inspect completed units.

Classification of Automatic Lathes

• Magazine loaded automatics: Machines used for producing components from separate blanks; also known as automatic checking machines.
• Automatic Bar Machines: Used to manufacture quality fasteners, such as bushings, shafts, rings, rollers, handles, etc., from bar/pipe stock.
• Based on number of work spindles: single spindle automatics vs. multiple spindle automatics.
• Based on purpose & arrangement: General & single purpose machines; horizontal vs. vertical

Type of Single Spindle Automatics

• Automatic cutting-off machine: Spindle, headstock, rear and front cross slides, and stock stop.

Tool layout and camdesign

• Pre-determined plan for machining operations.
  • Selecting best available machines
  • Determining sequence of operations
  • Choosing standard tooling (designing special tooling if needed)
  • Deciding cutting process parameters
  • Checking tool movement with respect to the work piece
  • Arranging operations for minimal cycle time
  • Calculating processing time & number of revolutions
  • Calculating cam periphery spacing
  • Drawing tool layout and cam details while verifying clearances

Machining Calculations: Turning

• Spindle Speed (N)
• Feed Rate (f)
• Depth of Cut (d)
• Machining Time (Tm)
• Material Removal Rate (MRR)

This quiz explores essential concepts related to lathe operations, including methods for holding workpieces, functions of various lathe components, and differences between turning and facing. Test your understanding of key terms and principles that are fundamental to metalworking with lathes.