The movement of the tool relative to the work is termed as “feed”. A lathe tool may have three types of feed-longitudinal, cross, and angular. When the tool moves parallel to the lathe axis, the movement is termed as longitudinal feed and is effected by the movement of carriage. When the tool moves at right angles to the lathe axis with the help of the cross slide the movement is termed as cross feed, while the movement of the tool by compound slide when it is swiveled at an angle to the lathe axis is termed as angular feed. Cross and longitudinal feed is both hand and power operated, but angular feed is only hand operated.
The feed mechanism has different units through which motion is transmitted from the head stock spindle to the carriage. Following are the units:
1.End of bed gearing
2.Feed gearbox
3.Feed rod and lead screw
4.Apron mechanism
End of bed bearing
The gearing serves the purpose of transmitting the drive to the lead screw and feed shaft, either direct or through a gearbox. In modern lathes, tumbler gear mechanism or bevel gear feed reversing mechanism is incorporated to reverse the direction of feed.
Tumbler gear mechanism
Tumbler gear mechanism is used to give the desired direction of movement to the lathe carriage, via lead screw or the feed shaft. The tumbler gearing comprise of two pinions mounted on a bracket. The bracket is pivoted about the 1st stud shaft. The design provides three positions of bracket: forward, neutral, and reverse. With the forward position, only one gear train, and the lathe carriage is moved towards the headstock. With the introduced only to reverse the direction of rotation, and the carriage is neutral position, the spindle is disengaged from the lead screw is disengaged from the lead screw or feed shaft gearbox.
Bevel gear feed reversing mechanism
The tumbler gear mechanism being a non-rigid construction cannot be used in a modern heavy-duty lathe. The clutch-operated bevel gear feed reversing mechanism incorporated below the headstock or in apron provides sufficient rigidity in construction.
fr. NTTF ( NETTUR TECHNICAL TRAINING FOUNDATION)
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