CUTTING TOOLS AND TOOL HOLDERS
Because cutting-tool materials are expensive, it is desirable to use as small amounts as possible. It is
necessary that the cutting tool should be supported in a strong, rigid manner to minimize deflection and
possible vibration. Lathe tools are supported in various types of heavy forged tool holders. The tool bit
should be clamped in the tool post with minimum overhang. If there is much overhang, tool chatter and
poor surface finish may result. Most lathe work is done with high-speed steel, carbide, or ceramic tools.
Where large tool bits are required, the heavy type of forged tool holder is used. It provides adequate
method of clamping and supporting the tool than is provided by an ordinary tool post. The tools used in
such cases have a heavy shank of Tool Steel or hot-rolled bar stock in which a carbide tip is brazed.
Most all of the lathe operations are done with simple, single point cutting tools. On right-hand and
left-hand turning and facing tools, the cutting takes place on the side of the tool so that the side rake
angle is important so deep cuts can be made. On the round-nose turning tools, cutoff tools, finishing
tools, and some threading tools, cutting takes place on or near the end of the tool, so that the back rake
is of importance, and is fed with light depths of cut.
TOOL HOLDERS
In most lathe work, the nose of the tool should be set exactly at the same height as the axis of rotation of
the work. Any setting below the axis causes the work to tend to climb up on the tool, and in most
operations you will need to set your tool a few thousandths of an inch above the axis, except for cutoff,
threading, and some facing operations.
Where there are more than I operation on a lathe are performed repeatedly in sequence, the time
required for changing and setting tools may make up as much as 50 per cent of the total time.
Quick-change tool holders are being used to reduce the time of tool changing.
The individual tools, preset in their holders, can be interchanged in the special tool post in a few
seconds. With some systems, a second tool may be set in the tool post while a cut is being made with
the first tool, and then be brought into proper position by rotating the post.