stock for reaming. The allowance for reaming
depends on the hole size.
When reaming, use a cutting speed about
two-thirds the speed you would use for a similar
size drill with the material being machined. Use a
slow, steady feed with an adequate supply of
cutting fluid. Remove the reamer from the hole
before stopping the machine.
Do not apply power if a hand reamer is
used, Figure 28-6. Use regular hand reaming
techniques. However, feed the reamer into the
hole with the tailstock handwheel.
28.2 BORING
Boring, Figure 28-7, is an internal machining
operation where a single-point cutting tool is
used to enlarge a hole. Boring is done to enlarge
a hole to exact size when a drill or reamer of the
proper size is not available. Its main purpose,
however, is to produce a hole that is concentric
with the outside diameter of the work.
The size of the hole to be bored determines the
type and size of boring bar to be used, Figure 28-8.
Always employ the largest bar possible as this gives
maximum support to the tool. The bar should
extend from the holder only far enough to permit
the tool to cut to the proper depth, Figure 28-9.
Set the tool on center, or slightly below, with
the boring bar parallel with tool travel. Check for
adequate clearance when the tool is at maximum
depth in the hole. Make your cuts in the same
manner as you would for external cutting.
28.3 KNURLING
Knurling, Figure 28-10, is a machining process
used to form horizontal or diamond-shaped serra-
tions on the circumference of the work. Knurling is
used to provide a gripping surface, change the
appearance of the work, or increase the work’s
diameter. It is done with a knurling tool mounted in
the lathe tool post, Figure 28-11. The knurled pattern
is raised by rolling the knurls against the metal. This
displaces the metal into the required pattern.
Straight and diamond pattern knurls can be produced
in coarse, medium, and fine pitch, Figure 28-12.
28.3.1 Knurling Procedure
If a knurling tool setup is not made properly,
the knurls will not track and quickly dull. The
following procedure is recommended:
1. Mark off the section to be knurled.
2. Adjust the lathe to a slow back gear speed
and a fairly rapid feed.
3. Place the knurling tool in the tool post and
bring it up to the work. Both wheels must
bear evenly with their faces parallel with the
work surface.
4. Start the lathe and slowly force the knurls
into the work surface until a pattern begins
to develop, Figure 28-13. Tool travel should
be toward the headstock. Engage the auto-
matic feed and let the tool travel across the
work. Flood the work with cutting fluid.
5. When the knurling tool reaches the proper
position, reverse spindle rotation and move
back across the work to the starting point.
Apply additional pressure to force the knurls
deeper into the work.
6. Repeat the operation until a full knurl is formed.
Chapter 28 Other Lathe Operations 451
Figure 28-6.
Do not use power when using a hand reamer on
the lathe.
Figure 28-7.
Boring or machining an internal opening on the
lathe. (Clausing Industrial, Inc.)