Centre lathe

Setting the tool height

• The cutting tool on the lathe must be set to the exact centre of the work-piece

• We use the centre of the tailstock to guide us to the correct height

Lathe parts

• Tailstock Can be moved along

slideways Can be clamped in any location Inside tapered to hold drill chuck

Lathe parts

• Carriage Moves along bed

between tailstock and headstock

Saddle – across the lathe

Apron – hangs down in front

Lathe parts

• Cross Slide Fitted on the Saddle Moves cutting tool at

right angles to lathe bed

Lathe parts

• Top Slide (Compound slide)

Fitted to top of Cross slide Carries toolpost and cutting

tool Can rotate to any angle Is used to turn tapers

Lathe parts

• Feed shaft Used to move the

Carriage automatically

• Lead screw Used when screw

cutting on the lathe

Lathe parts

• Toolpost Fitted on top slide and

carries the cutting tool or the cutting tool holder

Can adjust the height on some types

Can carry 4 different tool holders

Lathe parts

• Tool holders Used for holding

cutting tool bits Available in Right

hand, left hand and straight

Tool Holders

Cutting Tool Materials• Carbon Steels • High Speed Steel (HSS)• Stellite • Carbides• Diamond

Carbon Steels• Carbon steels start to soften at a

temperature of about 180oC. This limitation means that such tools are rarely used for metal cutting operations. widely used for woodworking and they can be used in a router to machine aluminum sheet up to about 3mm thick.

High Speed Steel (HSS)

• HSS tools are so named because they were developed to cut at higher speeds. They are tough and suitable for interrupted cutting and are used to manufacture tools of complex shape such as drills, reamers, taps, dies and gear cutters. Tools may also be coated to improve wear resistance.

Stellite

• A non-ferrous alloy of chromium and cobalt, so hard that it cannot be forged or machined except by grinding, it is usually used in the form of a tipped tool.

Carbides

• Also known as cemented carbides or sintered carbides .Have high hardness over a wide range of temperatures and high thermal conductivity. Can be shaped only by special grinding wheels and is always used in the form of a tipped tool.

Diamond• The hardest known substance is diamond. It

is most suited for light uninterrupted finishing cuts at almost any speed and is mainly used for very high speed machining of aluminum - silicon alloys, composites and other non - metallic materials.

Tool Forms

• Solid ToolsMade throughout in one material. Normally

HSS or carbon

Butt-Brazed

• Tools made by brazing or welding a piece of HSS to a high tensile steel shank.

Tipped Tool

• Have a tip of cemented carbide, etc, brazed to a blank of high tensile steel.

Tool Bit and Holder

• Tool bits are held in holders at an angle of about 15°

• Cutting Tools Can be High Speed

Steel held in tool holders

Can be also Ceramic (Tungsten carbide) bits held directly in toolpost

Cutting Tool Angle

• Clearance angle Ensures only the

cutting edge of the tool touches the work

Too much clearance causes chatter

Cutting tool angle• Rake Angle Allows the chip being cut

to flow out Changing the rake

changes the power used in cutting and the heat generated

Large rake = soft ductile materials

Small rake = hard brittle materials

Lathe operations

Facing off

Parallel Turning

Parallel Turning

Parallel Turning• The tool moved parallel to

the work and cylindrical shapes are formed

• Also known as sliding

Parallel Turning

• The student can Parallel turn the work on the lathe manually or use the automatic traverse option

Facing off

• The tool is moved at right angles to the work using the cross slide

• Flat surfaces are produced

Knurling

• A knurling tool is used to press a pattern onto a round section.

• The pattern is normally used as a grip for a handle.

• This provide a grip for the round parte.g. Screwdriver

Knurling

Parting off• If the student wants to cut

off the part they have turned, they can use the hacksaw and a vice or use the parting off tool on the lathe.

Boring

Boring Tools

Screw-cutting on the lathe• Lathes are also used to

cut threads in round bars

• These threads take up different profiles e.g iso (60°) ACME etc.

• These threads can be seen on bench vices, lathes etc.

CNC Lathes

• In Industry it is not efficient or profitable to make everyday products by hand.

• On a CNC machine it is possible to make hundreds of the same item in a day.

• First a design is drawn using design software, then it is processed by the computer and made using the CNC machine.

• In industry, CNC machines can be extremely large.

LATHE OPERATIONS  

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Producing a Cylindrical Surface

Taper Turning

Producing a Flat Surface

Drilling on a Lathe

Parting Off / Under Cutting

Radius Turning Attachment

Tool shape

• The shape of the tool and the angles of its ground faces will depends on:

The operation to be performedThe material which has to be machinedThe power & rigidity of the latheThe amount of material to be removedThe quality of finish desired.

Cutting tools

• We can put different shapes on the High speed tool bits to cut different shapes on the workpiece

Home work• Sketch and explain the following1. Solid tools2. Butt brazed 3. Tipped toolsSketch and explain the following tool shape• Fine finishing• Round nose rougher• Round nose• Internal screw cutting tool• Parting off tool• Knife tool• Form tool