Download - 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.
Accessories - Chucks
Figure: Three Jaw Chuck
Accessories - Chucks
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
Simple train with one idler
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.:
Simple train with one idler
Simple train with one idler
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:
Gear A = 40; Gear B = 100;and
Gear C = 45; Gear D = 75
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:
Gear A = 127; Gear B = 80;and
Gear C = 50; Gear D = 100
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.