Facing center drilling

Facing & Center Drilling
MACH 118: Lathe & Mill I

Thaddeus Stevens College of Technology
Machine Tool Technology


FACING AND CENTER DRILLING

Introduction
 Facing and center drilling the workpiece are often the first steps taken in a turning
project to produce a stepped shaft or a sleeve from solid material.

◦ Much lathe work is done in a chuck, requiring considerable facing and some center drilling.


OBJECTIVES
After completing this unit, you should be able to…

 Correctly set up a workpiece and face the ends.
 Correctly center drill the ends of a workpiece.
 Determine the proper feeds and speeds for a workpiece.
 Explain how to set up to make facing cuts to a
given depth and how to measure them.


FACING AND CENTER DRILLING

Setting Up For Facing
 Facing is done to obtain a flat surface on the end of cylindrical workpieces or on the
face of parts clamped in a chuck or face plate.

◦

Work is most often held in a three- or four-jaw chuck.


FACING AND CENTER DRILLING

Setting Up For Facing
 Round stock can be set
up using a dial indicator.

Fig. I-152
Setting up round stock in an
independent chuck with a dial indicator.


FACING AND CENTER DRILLING

Setting Up For Facing
 Square or rectangular stock
can be set up either with a
dial indicator or by using a
tool-holder turned backward.

Fig. I-153
Rectangular stock being set up by using a toolholder turned backward. The micrometer dial is used to center the
workpiece.

FACING AND CENTER DRILLING

Setting Up For Facing
Workpieces
can be chucked:
Normally.
Internally.
Externally.
Fig. I-156 Internal chucking position.

Fig. I-155
Normal chucking position.

Fig. I-157 External chucking position.


FACING AND CENTER DRILLING

Facing
 Facing from the center out produces a better finish, but it is difficult to cut on a
solid face in the center.

Fig. I-158 Facing from the center to the outside of the workpiece.


FACING AND CENTER DRILLING

Facing
 Heavier cuts may be taken when facing from the outside, and it is easier to work
to the scribed lines on the circumference of the work.

Fig. I-159 Facing from the outside toward the center of
the workpiece.


FACING AND CENTER DRILLING

Facing
 Machining should not be done on workpieces extending more than three x dia. from
the chuck face.


FACING AND CENTER DRILLING

Facing
 The tool point should be set to dead center.

Fig. I-160
Setting the tool to the center of the
workpiece using the tailstock center.


FACING AND CENTER DRILLING

Facing
 The tool point should be set to dead center.


FACING AND CENTER DRILLING

Facing
 The carriage may be locked
when taking facing cuts.

Fig. I-161 Carriage must be locked before taking a
facing cut.


FACING AND CENTER DRILLING

Facing
 Facing to length may be accomplished by trying a cut and measuring with a hook rule
or by facing to
a previously made layout line.

◦

A more precise
method is to use
graduations on the
micrometer collar
of the compound.

Fig. I-162 Facing to length
using a hook rule for measuring.


FACING AND CENTER DRILLING

Facing

 The compound slide is set parallel to the ways.

◦ The carriage is locked in place & a trial cut taken
with the micrometer collar set on zero index.

Fig. I-163 The compound set at 90 degrees
for facing operations.

Fig. I-164 Close-up of the compound set at 90 degrees.


FACING AND CENTER DRILLING

Facing
 The workpiece is measured with a micrometer & the desired length is subtracted
from the measurement.

◦

The remainder should be removed by facing.

 A short trial cut (about 1/8”) should again be taken on the finish cut and adjustment
made if necessary.

◦

Cuts can vary considerably, depending on machine size, horsepower, tooling, and setup.


FACING AND CENTER DRILLING

Facing
 Quite often the compound is kept at 30 degrees
for threading purposes.

◦

At this angle the tool feeds into the face of the work
.001 in. for every .002 in. that the slide is moved.

Fig. I-165

Fig. I-166

The compound set at 30 degrees.

Close-up of the compound set at 30 degrees.


FACING AND CENTER DRILLING

Facing
 Both right-hand and left-hand facing tools are used for facing work held on
mandrels.

◦ Care should be taken when machining pressure is
toward the small end of a tapered mandrel.

◦ Excessive pressure may loosen the workpiece on the mandrel.

Fig. I-171 Work held between centers
on a mandrel can be faced on both
sides with right- & left-hand facing tools.


FACING AND CENTER DRILLING

Speeds
 Speeds (rpm) for lathe turning are determined in essentially the same as
speeds for drilling tools.

◦ Work diameter is used instead of drill diameter.
 In facing operations, outside diameter of the work-piece has greater surface
speed than its center.

◦ The rpm should vary as the tool is moved in or out.
◦ Two or three speed changes may be required to get a uniform surface finish,
depending on the size of the work.


FACING AND CENTER DRILLING

Center Drills And Drilling
 When work is held and turned between centers, a center hole is required on
each end of the work.

◦ It must have a 60-degree angle to conform to the center and have a smaller drilled
hole to clear the center’s point.

 Facing the workpiece is almost always necessary before center drilling.

◦ An uneven surface can push sideways on the fragile center drill point and break it.


FACING AND CENTER DRILLING

Center Drills And Drilling
 Center drills are usually held in a drill chuck in the tailstock.

◦

Workpieces are most often supported & turned
in a lathe chuck for center drilling.

Fig. I-172
Center drilling a workpiece held in a chuck.


FACING AND CENTER DRILLING

Center Drills And Drilling
 Long workpieces are generally faced by chucking one end and supporting the other in
a steady rest.

◦

The greater the work
diameter & the heavier
the cut, the larger the
center hole should be.

Fig. I-173 Center drilling long
material supported in a steady rest.


FACING AND CENTER DRILLING

Center Drills And Drilling
 Drilling too deeply causes the center to contact only the
sharp outer edge of the hole, a poor bearing surface.

◦ It soon becomes loose & out of round, causing chatter and
roughness.

◦ Center drills often are broken from feeding the drill too fast with
the lathe speed too slow or with the tailstock
off center.

Fig. I-174 Correct and incorrect depth for center drilling.


Questions?