LATHE OPERATIONS - OD1645 - LESSON 1/TASK 1
d.
Cutting Oils.
(1) General. The chief purpose of cutting oil is to cool the cutter bit
and the workpiece. The name "coolant" is often given to the oil. A cutter
bit will last longer and will be capable of withstanding greater speeds
without overheating when a cutting oil is used. A cutting oil also helps
lubricate the cutter bits, improves the finish of the workpiece, guards
against rusting, and washes away chips from the cutting area.
(2) Use. In production operations, the practice is to flood the workpiece
and the cutter bit with cutting oil in order to obtain the full benefit of
its use. For effective cooling, it is important that the oil be directed at
the exact point of the cutter bit contact. A large stream at low velocity
is preferred to a small stream at high velocity. In small shops where pump
equipment is not available, cutting oils are used only for finishing and
delicate operations.
It is general practice in this case to apply the
cutting oil only when actually required.
(3) Types of Cutting Oils.
Cutting oils most commonly used and their
general applications are described in (a) through (g) below. Cutting oils
for specific lathe operations are listed in Table 3 on page 56.
(a) Lard Oil. Pure lard oil is one of the oldest and best cutting oils.
It is especially good for thread cutting, tapping, deep hole drilling, and
reaming. Lard oil has a high degree of adhesion or oiliness, a relatively
high specific heat, and its fluidity changes slightly with the temperature.
It is an excellent rust preventive and produces a smooth finish on the
workpiece. Because lard oil is expensive, it is seldom used in a pure state
but is combined with other ingredients to form good cutting oil mixtures.
(b) Mineral Oil.
Mineral oils are petroleum based oils that range in
viscosity from kerosene to light paraffin oils. Mineral oil is very stable
and does not develop disagreeable odors like lard oil; however, it lacks
some of the good qualities of lard oil such as adhesion, oiliness, and high
specific heat. Because it is relatively inexpensive, it is mixed with lard
oil or other chemicals to provide cutting oils with desirable
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