attachments and accessories

Lathe – Accessories & Attachments

Accessories:

• devices employed for holding and supporting the work and the tool on lathe are called its accessories.

Attachments:

• are used on a center lathe to increase production and efficiency and widen its scope of use for such works also which are normally carried out on this machine.

Lathe – Accessories & Attachments

AccessoriesCenters

Face Plates & Angle Plates

Dogs or Carriers

Chucks

Mandrels

Rests

AttachmentsBar Stops

Thread Chasing Dials

Taper turning

Milling

Grinding

Gear Cutting

Hydro-copying

Accessories - Centers

A – Ordinary Center E – Tipped (brazed) Center

B – Ball Center F – Insert type Center

D – Half CenterH – Use of half center1 – Half center2 – Facing tool

G - Pipe Center

C – Frictionless Center1 – Insert type center2 – Nut3 – Roller bearing4 – Thrust bearing5 - Housing

Accessories –Driving plates and Dogs

Figure: Eccentric TurningFigure: Driving Plate

Fig. Straight dog

Accessories - Chucks

Figure: Four Jaw Chuck

1- concentric circle,; 2 – chuck body;3 – Jaw screw; 4 – jaw; 5 – gripping surface; 6 – recess for back plate.


Figure: Three Jaw Chuck


Figure: Magnetic Chuck

1-work; 2-magnetic material; 3-keepers;4-face plates, 5-magnet

Figure: Hydraulic Chuck

1-cylinder; 2-air passage; 3-head stock spindle; 4-piston; 5-valves;; 6-piston rod; 7-link; 8-jaw; 9-guide; 10-sliding unit

Accessories - Collets

Figure: Collet Chuck

1-Bearing; 2-Spindle; 3-Nut; 4-Key; 5-Chuck; 6-Collet

Accessories –Face Plate and Angle Plate

Figure: Face Plate

Figure: Angle Plate

1-face plate; 2-balance weight; 3-elbow pipe; 4-clamping nut; 5-angle plate; 6-clamping nut

Accessories - Mandrels

Plain Mandrel

Step Mandrel Threaded Mandrel

Collar Mandrel

Accessories - Mandrels

Cone Mandrel

1-solid cone; 2-sliding cone; 3-nut

Gang Mandrel

1-fixed collar; 2-hollow workpieces; 3-movable collar; 4-nut

Expansion Mandrel1-sleeve; 2-tapered pin

Accessories – Steady Rest

Accessories – Follower Rest

Figure: Follower rest

Thread Cutting - Terminology

Fig. Elements of external and internal threads

Thread Cutting - Terminology

Fig. Single Start Fig. Double Start

Fig. Triple Start

Thread Cutting

Figure: General set-up of lathe for screw cutting

Thread Cutting - Change Gear Ratio

Thread Cutting – Gear Trains

Simple gear train Compound gear train

Cutting R.H. and L.H. Threads• Right Hand threads:

– Threads slope up to the right when screw is held vertically.

– The spindle and the lead screw will rotate in the same direction.

• Left Hand threads:– Threads slope up to the left when

screw is held vertically.– The spindle and the lead screw will

rotate in opposite direction.• This change of direction of rotation on

lathe is effected by tumbler gear or by using proper number of idlers.

Figure: R.H. Threads

Figure: L.H. Threads

Left Hand thread - ApplicationsWhere the rotation of a shaft would cause a conventional right-handed nut to loosen rather than to tighten due to fretting induced precession, e.g. on a left-hand bicycle pedal.In combination with right-handed threads in turnbuckles.

In some gas supply connections to prevent dangerous misconnections, for example in gas welding the flammable gas supply uses left-handed threads.

In Gold ornaments, e.g. ear studs.

Cutting metric thread on English standard lead screws or Vice Versa

• To cut metric threads on lathes having British standard lead screw:

• To cut British standard threads are to be cut on a lathe having lead screw of metric pitch:

Examples:• Calculate change gears for cutting R.H. threads of 2 mm pitch

on a lathe having lead screw of 6 mm pitch.

Soln.:

Simple train with one idler



Like this, we can have number of solutions and every solutionwill give the desired result.

Examples:• Calculate change gears for cutting L.H. threads of 1.5 mm

pitch on a lathe having lead screw of 6 mm pitch.

Soln.:

Simple train with two idlers

Simple train with two idlers

Examples:• Calculate change gears for cutting R.H.B.S.W. “V” threads of

12 TPI on a lathe having lead screw of 8 TPI.

Soln.:



Examples:• Calculate change gears for cutting threads of 1 mm pitch on a

lathe having lead screw of 8 mm pitch.

Soln.:

Such a ratio with 160 teeth in size is not available in the set. The maximum size is 120 only. Hence, a compound train has to be used.

Compound Gear Train with one idler:

Gear A = 20; Gear B = 80;and

Gear C = 30; Gear D = 60

Examples:• Calculate change gears to cut L.H. threads of 25 TPI on a lathe

having lead screw of 6 TPI.

Soln.:

If, however, these gears are not available, a compound train will be used. The calculation will be as follows:

Compound Gear Train with one idler:



Examples:• Calculate change gears to cut R.H. single start threads of 0.25”

pitch on a lathe having lead screw of 8 mm lead.

Soln.:

Compound Gear Train with no idler or two idlers:



Setting of Tools for Threading

Fig. Setting threading tool for internal threading

Fig. Setting threading tool for external threading

Feeding the Tool in Threading

Fig.a Straight ThreadFig.b Inclined feed

Fig.c Inclined feed using a form tool

Providing undercut

Attachments – Thread Chasing Dial

Figure: Thread Chasing Dial

Taper Turning

1001

=−

=L

dDTaper = 1 in 100

Half taper angle = =αtanL

dD

−

2 LdD

2−

=

Tail stock set-over method

Let,H = set-over required, mmD = larger diameter, mmd = smaller diameter, mmL = total length of work, mml = length of taper, mm

αsinLH =

αα tansin =α is very small and hence,

But,ldD

2tan −

=αldDLH

2−

=∴

Taper turning by swiveling the Compound rest

Fig. Turning taper by swiveling the compound rest

Taper turning attachment

Fig. Use of taper turning attachment

Taper turning byForm or Broad nose tool

Fig. Turning short taper by a form (broad nose) tool

Machining Time Calculations in Turning

• Cutting speed:

Where d = diameter of the work in mm;n = speed of the work in rpm.

• Feed: mm / rev. or mm / min.f (mm / min) = f (mm / rev) X n (rev / min)

• Machining time:

Where tm= machining time in min.; l = length of the job, mmf = feed in mm/rev.; n = speed in rpm.

attachments and accessories

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