Turning
Typical Parts Made with These Processes
Machine Components
Engine Blocks and Heads
Parts with Complex Shapes
Parts with Close Tolerances
Externally and Internally Threaded Parts
Products and Parts Made By These
Processes
Alternative Processes
Precision Casting
Powder Metallurgy
Powder Injection
Molding
Abrasive Machining
Thread Rolling
The Turning Process
Using Engine Lathes
Operate on all Types of Materials
Use of single-point tools
Skilled Labor
Low Production Rate
Tool Geometry
Rake Angle
Side Rake Angle
Cutting-Edge Angle
Relief Angle
Nose Radius
Typical Lathe and Its Various Components
Lathe Components
Bed: Usually made of cast iron. Provides a heavy rigid frame on which all the main components are mounted.
• Ways: Inner and outer guide railsn that are
precision machined parallel to assure accuracy of movement.
• Headstock: mounted in a fixed position on the
inner ways, usually at the left end. Using a chuck, it rotates the work.
• Gearbox: inside the headstock, providing multiple speeds with a geometric ratio by moving levers.
• Spindle: Hole through the headstock to which bar stock can be fed.
• Chuck: 3-jaw (self centering) or 4-jaw (independent) to clamp part being machined.
• Tailstock: Fits on the inner ways of the bed and can slide towards any position the headstock to fit the length of the work piece. An optional taper turning attachment would be mounted to it.
• Tailstock Quill: Has a Morse taper to hold a lathe center, drill bit or other tool.
• Carriage: Moves on the outer ways. Used for mounting and moving most the cutting tools.
• Cross Slide: Mounted on the traverse slide of the carriage, and uses a handwheel to feed tools into the workpiece.
• Tool Post: To mount tool holders in which the cutting bits are clamped.
• Compound Rest: Mounted to the cross slide, it pivots around the tool post.
• Apron: Attached to the front of the carriage, it has
the mechanism and controls for moving the carriage and cross slide.
• Feed Rod: Has a keyway, with two reversing pinion gears, either of which can be meshed with the
mating bevel gear to forward or reverse the carriage using a clutch.
• Lead Screw: For cutting threads.
• Split Nut: When closed around the lead screw, the carriage is driven along by direct drive without using a clutch.
• Quick Change Gearbox: Controls the movement of the carriage using levers.
• Steady Rest: Clamped to the lathe ways, it uses
adjustable fingers to contact the workpiece and align it. Can be used in place of tailstock to support long or unstable parts being machined.
• Follow Rest: Bolted to the lathe carriage, it uses adjustable fingers to bear against the workpiece opposite the cutting tool to prevent deflection.
Lathe Accessories
Carriage and Cross Slide Stops
Devices for Turning Parts with Various Tapers
Milling, Sawing, Gear-Cutting, and Grinding Attachments
Various Attachments for Boring, Drilling, and
Thread Cutting
More Tool Geometry
Lathe Operations
Form Tools
Boring
Drilling
Parting
Grooving
Thread Cutting
Knurling
Cutting Operations Performed on a Lathe
Above Left: Example of Boring Above Right: Example of Drilling Below Left: Example of Thread Cutting Below Right: Example of Grooving
Types of Lathes
Bench Lathes
Special Purpose Lathes
Tracer Lathes
Automatic Lathes
Automatic Bar Machines
Turret Lathes
Computer-Controlled Lathes
Turret Lathe
Computer-Controlled Lathe
Things to Remember About Machining Parts on Lathes
Takes considerable amount of time
High Production Costs
Wastes Material
Not as Economical as Forming or Shaping
Boring and Boring Machines
What is Boring
Performed to enlarge a hole made previously.
Used for circular internal profiles in hollow
workpieces
Boring Machines
Small pieces – lathe
Large pieces – boring mill
Horizontal vs Vertical
Boring mills
Perform various
operations: TURNING, FACING, GROOVING, CHAMFERING
Horizontal Boring Mill
Vertical Boring Mill
Large pieces can be machined on a vertical mill
Jig Boring Machines
Vertical machines
High precision bearings
Used to make jigs and fixtures
Being replaced by CNC boring machines
Considerations
Through holes, rather than blind holes, should be specified.
Smaller length-bore diameter ratios
Interrupted internal surfaces should be
avoided.
Milling and Milling Machines
Milling
The Process of cutting away material by feeding a
workpiece past a rotating multiple tooth cutter.
Types of Milling
Peripheral Milling
Peripheral Milling is when the cutter is longer than the width of the cut.
a.k.a.- Slab Milling
The axis of the cutter is usually parallel to the work piece surface.
Face Milling
the cutter is mounted on a spindle having an axis of rotation perpendicular to the
workpiece surface.
Leaves feed marks on the machined surface.
End Milling
The cutter generally rotates on an axis vertical to the workpiece.
It can be tilted to machine tapered surfaces.
Cutting teeth are located on both the end face of the cutter and the periphery of the cutter body.
Can produce a variety of surfaces at any
depth.
Conventional Milling
a.k.a- Up Milling
The Direction of cutter rotation opposes the
feed motion.
Climb Milling
a.k.a.- Down Milling
The direction of cutter rotation is the same as
the feed motion.
Other Types of Milling
Straddle Milling
Form Milling
Slotting and Slitting
Uses circular cutters
Tool holders
Arbor Cutters
Mounted on an arbor
Used in peripheral, face, straddle and form milling.
Shank-Type Milling
Cutter and shank are one peice
Design and Operating Guidelines
Basic cutters should be used as much as possible.
Avoid expensive special cutters.
•Chamfers should be specified instead of radii.
•Chamfer-A furrow or groove, as in a column.
•Avoid internal cavities and pockets with sharp corners.
•Due to the difficulty of doing them.
Troubleshooting
Tool Breakage Tool material lacks toughness, improper angles.
Excessive Tool Wear improper tool material, improper tool fluids.
Rough Surface Finish Feed per tooth too high, tool chipped or worn.
Chatter Marks Insufficient stiffness of system, external vibrations.
Breakout Lead angle too low, feed and depth of cut too high.
Milling Machines
First Milling Machine
Built in 1820 by Eli Whitney
Column-and-Knee type
Most common milling machines.
Basic Components
Work Table
Saddle
Knee
Overarm
Head
Bed Type
Work table is mounted is mounted directly on the bed.
Not versatile
High Stiffness
Used for high production work
Other Milling Machines
Planer-Type
Several heads and cutters able to mill different surfaces
•Rotary-Table
•One or more heads for face milling.
•Computer Numerical Control
•Able to mill, drill, bore and tap with repetitive accuracy
•Profile Milling Machines
•5 axes of movement.
Planning and Shaping
Planning
Large workpieces 25m X 15m
Work piece is mounted on a table and travels back and forth along a straight path.
Cutting speeds can get up to 120 m/min with 150 hp
Shaping
Tool does the moving
Small less than 1m X 2m
Gear milling
Uses a rotating form cutter
Gear blanks are
indexed after each cut
Is a low production process
Gear teeth are
produced individually
