LATHE OPERATIONS - OD1645 - LESSON 1/TASK 1
(1) General. Straight turning may he performed upon a workpiece supported
in a chuck, but the majority of workpieces turned on an engine lathe are
turned between centers. Turning is the removal of metal from the external
surface of cylindrical workpieces using various types of cutter toolbits.
(2) Mounting Workpieces For Straight Turning.
good condition and carefully aligned if the turning operation is to be
If necessary, regrind the centers and check their alignment.
When turning the workpieces, considerable heat will be generated causing the
workpiece to expand. Centers that are too tight may cause binding of the
workpiece due to this expansion.
The tailstock center or the deadcenter
must be well lubricated to prevent the workpiece from overheating.
center hole and the tailstock center should be lubricated before the cutting
operation with a mixture of white lead and motor oil. During the turning
operation, feel the deadcenter frequently to determine whether lubrication
or adjustment is necessary.
(3) Proper Cutter Bits For Straight Turning.
Straight turning is
accomplished with the left-hand turning cutter bit, the right-hand turning
cutter bit, or the roundnose turning cutter bit.
Wherever possible, the
right-hand turning cutter bit or a roundnose bit ground for right-to-left
turning is used and the hit is fed toward the headstock. If circumstances
demand that the bit feed from left to right, such as in turning up to a
shoulder, the left-hand cutter bit is used.
The roundnose turning cutter
bit is especially efficient for finishing cuts.
(4) Position of Cutter Bit For Straight Turning. The cutter bit should be
locked in the cutting toolholder and the holder should be fixed to the
toolpost so that the cutting edge of the bit touches the workpiece surface
at about 5 above the horizontal centerline of the piece (figure 26 on page
60) since this position gives the bit a better cutting action. The distance
above the center is governed by the diameter of the workpiece and the front
clearance angle of the cutter bit. As a general rule, the point of contact
of the cutting edge is raised 3/64 inch above the center for each