LATHE OPERATIONS - OD1645 - LESSON 1/TASK 1
this bit is ground flat and has clearance ground on both sides so that it
will cut on both sides. For American (National) Standard screw threads, the
bit is ground with a flat at the nose to cut the flat root of the thread.
The width of the flat at the nose is determined by the pitch of the screw
thread that is to be cut.
(9) Special Types Of Lathe Cutting Tools. Besides the common cutter bits,
special lathe operations and heavy production work require special types of
cutting tools (figure 13 on the following page). Some of the more common
special tools will be described in subparagraphs (a) through (e) below.
(a) Tipped Cutter Bits. Tungsten carbide, tantalum carbide, and oxide
or ceramic tipped cutter bits are commonly used in production work where
high speeds and heavy cuts are necessary, and where exceptional hard and
tough materials are encountered.
The tipped cutter bit generally has a
shank size larger than the common cutter bit and is mounted in an openside
cutting toolholder, a turret tool block, or directly in the toolpost of the
lathe.
Tipped cutter bits come in shapes for use in left-hand and right-
hand turning, general purpose work and cutting threads.
(b) The Threading Tool With Toolholder. The threading tool (figure 13)
with the toolholder is used where considerable thread cutting is to be
accomplished. It is used in a specially designed toolholder which in turn
mounts to the lathe toolpost. The threading tool has a formed cutter which
needs to be ground on the top surface only for sharpening, the thread form
being accurately shaped over a large arc of the tool.
As the surface is
worn away by grinding, the cutter can be rotated to the correct cutting
position and secured there by the setscrew.
(c) Knurling Tool.
The knurling tool (figure 13) consists of two
cylindrical wheels, called knurls, which rotate in a specially designed
toolholder. The knurls contain teeth which are rolled against the surface
of the workpiece to form depressed patterns on the workpiece. The knurling
tool accepts different pairs of knurls, each pair having a different pitch.
The diamond pattern is
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