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FEED MECHANISM IN LATHE

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• Movement of the tool relative to w/p is termed as feed• Three types of feed in latheo Longitudinalo Crosso Angular• Feed mechanism has different units through which motion is

transmitted from head stock spindle to the carriage End of bed gearing Feed gear box Feed rod & lead screw Apron mechanism

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END OF BED GEARING• This gearing serves the purpose of transmitting the drive to the lead

screw and feed shaft either direct or through gear box• Different mechanisms are Tumbler gear mechanism Bevel gear feed reversing mechanism

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Tumbler gear mechanism• Tumbler gears are used to give the desired direction of motion to

the lathe carriage• Tumbler gearing consists of two pinions mounted on a bracket• The bracket is pivoted about the 1st stud shaft• The design provides three position of the bracket:- forward,

neutral and reverse

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• With the forward position, only one gear is in contact between the lathe spindle and the main gear train, and the lathe is moved towards the head stock

• With the reverse, the drive is through two gears • Second gear is introduced only to reverse the direction of rotation

and the carriage is moved away from the head stock• If the tumbler gears are brought into the neutral position, the

spindle is disengaged from the lead screw or feed shaft gear box

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Bevel gear feed reversing mechanism• Incorporated below the head stock or in apron• It is clutch operated• The motion is communicated from the spindle gear to the gear

on the stud shaft through intermediate gear• Bevel gear is attached to the gear on the stud shaft and both of

them can freely rotate on shaft as shown in figure• All bevel gears have equal no: of teeth• Bevel gear on the extreme right end can also rotate freely in its

shaft• A clutch is keyed to the shaft by a feather key and may shifted

right or left by the lever• So three positions can be achieved by the clutch

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• Clutch may engage with gear(8) or with gear (10) or it may remain in neutral position.

• When the clutch engages with bevel gear (8), gear (3) and the lead screw, rotates in the same direction as gear (2)

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FEED GEAR BOX• Also called quick change gear box• Fitted directly below the head stock assembly • power from the lathe spindle is transmitted to quick change gear box

through gears• This gear box contains a number of different sizes of gears which

provides a means to o change the rate of feed and o the ratio between revolution of the head stock spindle and the

movement of the carriage • Different arrangements are Sliding gear & sliding clutch mechanism Gear cone & tumbler gear mechanism Sliding key mechanism Combination of any two or more of the above

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Sliding gear & sliding clutch mechanism• The cone pulley is not keyed to the spindle and revolves freely on it• The gear (D) is called bull gear which is keyed to the spindle• In order to transmit motion from the step cone pulley to the

spindle to obtain direct speed a lock pin is introduced into the hole provided on the face of the cone pulley

• This lock pin engages the bull gear (D) with cone pulley • The number of different speeds obtained by the lathe spindle

depends on the no: of steps on the cone pulley

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Gear cone & tumbler gear mechanism• A number of different sized gears are keyed to the driving shaft in

the form of a cone• A sliding gear which is keyed to the driven shaft meshes wit idler

gear • Idler gear is held in a bracket• Bracket is pivoted on the driven shaft• To change the gears the handle is pulled downwards to slide the

whole assembly of gears and to the proper position and the idler is the n engaged with the cone

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Sliding key mechanism• It consists of a cone of gears which is mounted on a hollow shaft• By a sliding key any of the gears can be engaged with the shaft • The cone of gears is permanently in mesh with the driven shaft

gears transmit motion from the keyed gear to the driven shaft

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DRIVE OF FEED ROD & LEAD SCREW• The motion is transmitted from the spindle gear through the

tumbler gears and change gears to the shaft• On to the shaft twelve gears are arranged• Twelve different speeds may be obtained by the shaft (7) and sliding

gear • With the use of sliding key and four additional gears 48 speeds may

be obtained

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APRON MECHANISM• Transforms the rotary motion of the feed rod and lead screw into

feed motion of the carriage• A sliding gear mounted on the feed rod drives the worm gear

through other gears

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• To get an automatic longitudinal motion a knob on the apron is turned • This causes the cone clutch mounted on the worm gear shaft to be engaged • The motion is transmitted from the worm gear through the cone clutch and

driving gears to the pinion• Pinion is mounted on the driving gear shaft• Pinion meshes with rack and the carriage automatic longitudinal feed motion

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• To obtain automatic cross feed, knob (19) is turned• This causes second pair of cone clutch to be engaged (18)• When the worm gear rotates, motion is transmitted to the cross

feed screw (4) through the cone clutches (9) and (18)

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• To disengage the feed, a lever (20) is operated• The mechanism also ensures the when the half nut is engaged with

the lead screw the worm drops down disconnecting the feed motion