Use a sufficient amount of grease, oil or other
imagination as to the various tooling and setup
available lubricant on the jaws of the center rest and
follower rest to prevent "seizing" and scoring the
workpiece. Check the jaws frequently to see that they
PLANNING THE JOB
do not become hot. The jaws may expand slightly if
they get hot and push the work out of alignment
It is important for you to study the blueprint of the
(when the follower rest is used) or bind (when the
part to be manufactured before you begin machining.
center rest is used). If you are using a center rest or
Check over the dimensions and note the points or
follower rest that is equipped with ball bearings, no
surfaces from which they are laid out. Plan the steps
lubrication is necessary.
of your work in advance to determine the best way to
proceed. Check the overall dimensions and be sure
the stock you intend to use is large enough for the job.
ENGINE LATHE OPERATIONS
For example, small design features, such as collars on
pump shafts or valve stems, will require that you use
Up to this point, you have studied the preliminary
stock of much larger diameter than that required for
steps leading up to performing machine work on the
the main features of the workpiece.
lathe. You have learned how to mount the work and
the tool, and which tools are used for various
CUTTING SPEEDS AND FEEDS
purposes. The next step is to learn how to use the
lathe. We will now cover some of the basic
Cutting speed is the rate at which the surface of
operations that you will accomplish on the engine
the work passes the point of the cutting tool. It is
lathe.
expressed in feet per minute (fpm).
Remember that accuracy is the prime requisite of
To find the cutting speed, multiply the diameter of
a good machine job; so before you start, be sure that
the work (DIA) in inches times 3.1416 times the
the centers are true and properly aligned, that the
number of revolutions per minute (rpm) and divide
work is mounted properly, and that the cutting tools
by 12.
are correctly ground and sharpened.
As we cover the various operations that you will
CS = DIA 3.1416 rpm
perform on a lathe, remember the tooling used in your
12
shop may be different from what is pictured in this
manual. You may use different toolholders or cutting
The result is the peripheral or cutting speed in
tools, but the operations are basically the same.
fpm. For example, a 2-inch diameter part turning at
Always remember that you are only limited by your
100 rpm will produce a cutting speed of
2 3.1416 100
= 52.36 fpm
12
If you have selected a recommended cutting
speed from a chart for a specific type of metal, you
will need to figure what rpm is required to obtain the
recommended cutting speed. Use the following
formula:
CS 12
rpm =
DIA 3.1416
Recommended cutting speeds in fpm for turning
carbon and alloy steels using either high-speed steel
or carbide tool bits can be found in the cutting speeds
section of the current edition of the Machinery's
Figure 6-59.--Follower rest supporting screw while thread is
Handbook.
being cut.
6-33