LATHE OPERATIONS - OD1645 - LESSON 1/TASK 1
(f) Boring Bar Cutting Toolholder.
A lathe boring bar cutting
toolholder comes in several commercial types (figure 10 on the following
page). It consists of three parts: the holder, the interchangeable end cap,
and the boring tool bar. The boring tool bar is a rod with one end threaded
to accept an end cap. Three end caps are supplied; each end cap is slotted
at different angles to accept a cutter bit. The standard angles are 30,
45, and 90.
Plain boring toolholders without caps are often made to
accept cutter bits at each end, one having a 90 slot, and the other having
a 45 slot. The holder is made of forged steel. It has a shank similar to
that of the other cutting toolholders.
The holder is secured to the
toolpost by the lathe toolpost screw. The boring bar is adjustable in the
holder and can be locked in any desired position.
Lathe Cutting Tools
A machine tool is no more efficient than its cutting tool.
There is nothing in shop work that should be given more thoughtful
consideration than cutting tools.
Time is always wasted if an improperly
shaped tool is used. The cutting action of the tool depends on its shape
and its adjustment in the holding device.
Lathe cutter bits may be
considered as wedges which are forced into the material to cause
compression, with a resulting rupture or plastic flow of the material. The
rupture or plastic flow is called cutting. To machine metal efficiently and
accurately, it is necessary that the cutter bits have keen, well-supported
cutting edges, and that they be ground for the particular metal being
machined and the type of cut desired.
Cutter bits are made from several
types of steel, the most common of which are described in the following
(1) Carbon Steel. Carbon steel, or tool steel is high in carbon content,
hardens to a high degree of hardness when properly heated and quenched. The
carbon-steel tool will give good results as long as constant care is taken
to avoid overheating or "bluing," since the steel will lose its temper or
hardness at a relatively low heat becoming ineffective as a cutting tool.
For low-speed turning, high carbon steels give satisfactory results and are
more economical than other materials.