Square, round, and "V" grooves and the tools that are
The grooving tool is a type of forming tool. It is
ground without side rake or back rake and is set to the
work at center height with a minimum of overhang.
The side and end relief angles are generally somewhat
Figure 6-66.--Three common types of grooves.
less than for turning tools. When you machine a
groove, reduce the spindle speed to prevent the
chatter that often develops at high speeds because of
If the job requires that the hole be reamed, it is
the greater amount of tool contact with the work.
good practice to first take a cleanup cut through the
hole with a boring tool. This will true up the hole for
DRILLING AND REAMING
the reaming operation. Be sure to leave about 1/64
inch for reaming. The machine reamer has a taper
Drilling operations performed in a lathe differ
shank and is held in and fed by the tailstock. To avoid
very little from drilling operations performed in a
overheating the reamer, set the work speed at about
drilling machine. For best results, start the drilling
half that used for the drilling operation. During the
operation by drilling a center hole in the work, using a
reaming operation, keep the reamer well lubricated.
combination center drill and countersink. The
This will keep the reamer cool and also flush the chips
combination countersink-center drill is held in a drill
from the flutes. Do not feed the reamer too fast; it
chuck that is mounted in the tailstock spindle. After
may tear the surface of the hole and ruin the work.
you have center drilled the work, replace the drill
chuck with a taper shank drill. (NOTE: BEFORE
you insert any tool into the tailstock spindle, inspect
the shank of the tool for burrs. If the shank is burred,
Boring is the machining of holes or any interior
remove the burrs with a handstone.) Feed the drill
cylindrical surface. The piece to be bored must have
into the work by using the tailstock handwheel. Use a
a drilled or core hole, and the hole must be large
coolant/lubricant whenever possible and maintain
enough to insert the tool. The boring process merely
sufficient pressure on the drill to prevent chatter, but
enlarges the hole to the desired size or shape. The
not enough to overheat the drill.
advantage of boring is that you get a perfectly true
If the hole is quite long, back the drill out
occasionally to clear the flutes of metal chips. Large
Work to be bored may be held in a chuck, bolted
diameter holes may require you to drill a pilot hole
to the faceplate, or bolted to the carriage. Long pieces
first. This is done with a drill that is smaller than the
must be supported at the free end of a center rest.
finished diameter of the hole. After you have drilled
the pilot hole to the proper depth, enlarge the hole
When the boring tool is fed into the hole in work
with the finish drill. If you plan to drill the hole
being rotated on a chuck or faceplate, the process is
completely through the work, slow down the feed as
called single point boring. It is the same as turning
the drill nears the hole exit. This will produce a
except that the cutting chip is taken from the inside.
smoother exit hole by causing the drill to take a finer
The cutting edge of the boring tool resembles that of a
cut as it exits the hole.
turning tool. Boring tools may be the solid forged
type or the inserted cutter bit type.
If the twist drill is not ground correctly, the drilled
hole will be either excessively oversized or out of
When the work to be bored is clamped to the top
round. Check the drill for the correct angle,
of the carriage, a boring bar is held between centers
clearance, cutting edge lengths and straightness
and driven by a dog. The work is fed to the tool by the
before setting it up for drilling. It is almost
automatic longitudinal feed of the carriage. Three
impossible to drill a hole exactly the same size as the
drill regardless of the care taken in ensuring an
the countersunk center holes at the ends to fit the lathe
accurately ground drill and the proper selection of
speeds and feeds. For this reason, any job that
requires close tolerances or a good finish on the hole
with a fly cutter held by a headless setscrew. The
should be reamed or bored to the correct size.