The feed gearbox or quick-change gearbox is fitted directly below the head stock assembly. Power from the lathe spindle is transmitted through gears to the quick-change gearbox. This gear box contains a number of different sizes of gear which provides a means to change the rate of the feed, and the ratio between the revolutions of the head stock spindle and the movement of the carriage for thread cutting by altering the speed of motion of feed rod or lead screw.
The arrangement which are employed in feed gear boxes to obtain multiple speeds and different rates of feed are:
1.Sliding gear mechanism
2.Sliding clutch mechanism
3.Gear cone and tumbler gear mechanism
4.Sliding key mechanism
5.Combination of any two or more of the above
Feed rod
The feed rod is a long shaft that has the key way extending from the feed box across and in front of the bed. The power is transmitted from the lathe spindle to the apron gears through a feed rod via large number of gears. The feed rod is used to move the carriage or cross-slide for turning, boring, facing and all other operations except thread cutting.
Lead screw
The lead screw is a long threaded shaft used as a master screw, and is brought into operation only when threads have to be cut. In all other times the lead screw is disengaged from the gear box and remains stationary, but this ma be used to provide motion for turning, boring, etc. in lathes that are not equipped with a feed rod.
Apron Mechanism
The apron mechanism is used for transforming rotary motion of the feed rod and the lead screw into feed motion of the carriage. The mechanism also ensures that when the half nut is engaged with the lead screw the worm drops down disconnecting the feed motion. This arrangement is called foolproof arrangement and saves the machine from any damage.
fr. NTTF ( NETTUR TECHNICAL TRAINING FOUNDATION)
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