The Metalworking Lathe

Unit 58Metalwork Technology and

Practice

Lathe Operation Principle

• Lathes operate on the principle of a cutting tool removing metal as it is being fed into a revolving work piece. (Fig 58-2 pg. 451)

Kinds of Lathes• Manually Operated Lathe: Used to make single parts

and small quantities of multiple parts or for repair of worn parts.

• Screw Machines and Turret Lathes: Used for production runs of a few hundred parts.

• Numerically Controlled and CNC: Used for short but rapid production runs. These are replacing the Manual Lathes.

• Automatic Lathes: Used for production runs of thousands identical parts

• Vertical Turret Lathes: Used to machine parts of a large diameter.

Sizing Lathes• Lathes come in various sizes• Lathes are sized by the swing and bed length.• Swing: Is the largest diameter work piece that

can be turned on the machine.– The swing is measured by the distance from the

center point of the chuck to the bottom of the bed. Multiply this measurement times two to reach the largest diameter stock that can be turned.

– The bed is measured from front to the back of the machine.

– (See Fig. 58-9 pg 453)

Lathe Examples

• 7” x 12” Lathe• 13” x 40” Lathe

Lathe Main Parts• Bed: The main frame upon which the machine

is built.• Headstock: Always on the left hand side of the

bed. This contains the drive mechanisms of the lathe (motor). This part will accept different chucks.

• Tailstock: Always clamped to the right side on the lathe bed. This part moves on the bed. This part will accept live centers, dead centers, drill chucks, tapered shank drills, and reamers.

• Both headstock and tailstock contain spindles.

1

2

3

56

7 9

8 10

12

1415

13

11

4

Headstock Drive System• Belt Driven: This is the most common upon

older lathes. A V-belt will drive all the moving parts off the electric motor.

• Gear Driven: A series of gears operate the moving parts

• V-belt and Manual-shift systems require the operator to change speeds by changing the belts to different pulleys.

• Lever-shift systems and variable speed drive systems allow the operator to change speeds by the movement of a lever.

Emergency Foot Stop

Feed Change Levers

Speed Change Levers

Main Power Switch

Chuck

Tool Post Compound Rest Knob

Bed ways Tailstock

Power Feed Clutch

Cross SlideCarriage Hand Wheel

Friction Clutch

Tailstock Handle

Headstock

Carriage Feed

• Longitudinal Feed: When the tool is fed along the work, parallel with the bed.– Turning– Boring

• Cross Feed: When the tool is fed across the end of the work piece.– Facing

• (See Fig. 58-17 pg. 456)

Carriage Control• (See Fig. 58-20 pg. 457)• Apron Handwheel: Used for manual

longitudinal movement.• Cross-feed Knob: Used to move the

cross slide in and out manually.• Compound Rest: Holds the toolholder and

cutting tool that is mounted on the cross- slide which is fed manually with the compound-rest knob.

Emergency Foot Stop

Feed Change Levers

Speed Change Levers

Main Power Switch

Chuck

Tool Post Compound Rest Knob

Bed ways Tailstock

Power Feed Clutch

Cross SlideCarriage Hand Wheel

Friction Clutch

Tailstock Handle

Headstock

Lathe Safety

Safety Precautions

• Always wear safety glasses• Do not wear loose clothing or long sleeves

– Short sleeves are recommended• Never wear a ring or watch

– Rings and watches can get caught in revolving work or lathe parts

– If metal objects would fall on the hand this would cause the ring to bend or break. Removing a bent ring is painful!!!

Safety Precautions• Know your lathe parts

– Not knowing what certain levers do and how they operate could can be dangerous

– Know where your emergency shut down switches are located at

• Do not operate a lathe without the designed safety features

• Stop the lathe then shut off the power when checking measurements and removing stock from chuck or spindle

Safety Precautions• Do not attempt to measure revolving parts• If the machine is equipped, use the emergency

foot stop to stop the lathe. Never try to stop the lathe by hand!!!

• Never use a rag or paper towel to clean the parts while they are revolving in the lathe

• Make sure that all parts are secured tightly in the lathe before starting. Parts could fly out if they are not.

Safety Precautions• The chuck key is always part of your hand while

installing parts into the chuck. Never remove your hand from the chuck key until all parts are secured properly and the chuck key has been placed in its designated location.

• If the lathe is started with the chuck key in place the following could happen– The chuck key could fly out and injure someone or hit the lights– The chuck key could become jammed against the lathe bed,

damaging the wrench, lathe bed, chuck, and lathe spindle

Safety Precautions• Keep the floor free from grease, oil, metal cutting

tools, and work pieces• No horseplay• Remove the metal chips / shavings from the

lathe with a chip brush. Never use a cloth or your hands.

• Move the carriage out of the way or down the bed while polishing, filing, cleaning, and when making adjustments to the work.

Methods of Holding Workpieces in a Lathe

Unit 59Metalwork Technology and

Practice

Spindle Noses• Headstock Spindle: Where all work piece

holding devices are attached to and driven by.• Three types of spindle noses:

– Threaded Spindle Nose: Accommodates chucks and face plates.

– Cam-Lock Spindle Nose: Notched rods attached to the back of the chuck are aligned with holes on the spindle face.

– Long Taper Key-Drive Spindles: The chuck is placed so that the key on the spindle nose lines up with the keyway in the chuck.

– See Fig. 59-1, 59-2, and 59-3)

Lathe Chucks• Five Kinds of Lathe Chucks:

– Four Jaw– Three Jaw– Collet – Spindle– Step

• (See Fig 59-4, 59-5, 59-6, 59-7, 59-8, and 59-9 on pgs. 461, 462, and 463)

• To install and remove a chuck follow the instructions laid out in section 59-3 on pgs 462 and 463

LATHE CUTTING TOOLS, TOOLHOLDERS, CUTING

SPEEDS, AND FEED SELECTION

UNIT 60Metalwork

Technology and Practice

Tool Bits

• Defined: Cutting tools for lathes• Types of Tool Bits

– Left Hand Turning Tool– Left Hand Facing Tool– Right Hand Turning Tool– Right Hand Facing Tool

– Round Nose– Round Nose Turning Tool– Threading Tool– Boring Tool– Cut-Off Tool– Inside Turning Tool

Lathe Tool Composition

• High Speed Steel• Cast Alloys• Cemented Carbide• Ceramics• Cubic Boron Nitride• Diamond Lathe Cutting Tool Bits

Cutting Tool Terms• Cutting Edge: The part that does the cutting

– Side Cutting Edge– End Cutting Edge

• Face: Top Tool Surface• Flank: Side of the tool below the side cutting edge• Nose: Point of the tool• Nose Angle: Angle formed by the side cutting edge and

the end cutting edge• Nose Radius: The dimension of the arc that forms a

round nose• Shank: Body of the tool

Cutting Tool Terms (cont.)• Side Cutting Edge: The angle formed by

the side cutting edge• End Cutting Edge: The angle formed by

the end cutting edge• Side Relief: The angle between the tool

flank and the original side of the tool• End Relief: The angle between the end of

the tool and a line drawn 90 degrees to the base of the toolholder

Cutting Tool Terms (cont.)

• Left hand cutting tool: Has cutting edge on the right

• Right hand cutting tool: Has cutting edge on the left

ToolHolders

• The NCWHS lab uses a multiple tool post, tool holder system.

• The tool bit is inserted into a block where four tool bits can be utilized

Lathe Tool Post Systems