Machinery Repairman

Figure 6-64.—Machining to a shoulder.
scribe the exact location of the shoulder on the work.
Next, use a parting tool to machine a groove 1/32 inch
from the scribe line toward the smaller finish diameter
end and 1/32 inch larger than the smaller finish
diameter. Then, take heavy cuts up to the shoulder
made by the parting tool. Finally, take a finish cut
from the small end to the should scribe line. This
procedure eliminates detailed measuring and speeds
up production.
PARTING AND GROOVING
One of the methods of cutting off a piece of stock
while it is held in a lathe is a process called parting.
This process uses a specially shaped tool with a
cutting edge similar to that of a square nose tool. The
parting tool is fed into the rotating work,
perpendicular to its axis, cutting a progressively
deeper groove as the work rotates. When the cutting
edge of the tool gets to the center of the work being
parted, the work drops off as if it were sawed off.
Parting is used to cut off parts that have already been
machined in the lathe or to cut tubing and bar stock to
required lengths.
Parting tools can be the inserted blade type or can
be ground from a standard tool blank. They may also
be brazed on carbide or carbide inserts. Figure 6-65
shows two basic types of parting tools. For the tool to
have maximum strength, the length of the cutting
portion of the blade that extends from the holder
should be only slightly greater than half the diameter
of the work to be parted. The end cutting edge of the
tool must feed directly toward the center of the
workpiece. To ensure this, place a center in the
tailstock and align the parting tool vertically with the
tip of the center. The chuck should hold the work to
6-37
Figure 6-65.—Parting tools.
be parted with the point at which the parting is to
occur as close as possible to the chuck jaws. Always
make the parting cut at a right angle to the centerline
of the work. Feed the tool into the revolving work
with the cross-slide until the tool completely
separates the work.
Cutting speeds for parting are usually slower than
turning speeds. You should use a feed that will keep a
thin chip coming from the work. If chatter occurs,
decrease the speed and increase the feed slightly. If
the tool tends to gouge or dig in, decrease the feed.
Grooves are machined in shafts to provide for tool
runout in threading to a shoulder, to allow clearance
for assembly of parts, to provide lubricating channels,
or to provide a seating surface for seals and O-rings.