Machinery Repairman

narrow slots, part thick stock, saw thin stock, or saw
hard alloy steel. Soft metals, such as copper and
babbitt, or nonmetallic materials, such as bakelite,
fiber, or plastic, require their own style of slitting saw.
Parting with a slitting saw leaves pieces that are
reasonably square and that require you to remove a
minimum of stock to finish the surface. You can cut
off a number of pieces of varying lengths and with
less waste of material than you could saw by hand.
A coarse-tooth slitting saw is best to saw brass
and to cut deep slots. A fine-tooth slitting saw is best
to saw thin metal, and a staggered-tooth slitting saw is
best to make heavy deep cuts in steel. You should use
slower feeds and speeds to saw steels to prevent cutter
breakage. Use conventional milling to saw thick
material. To saw thin material, however, clamp the
stock directly to the table and use down milling.
Then, the slitting saw will tend to force the stock
down on the table. Position the work so the slitting
saw extends through the stock and into a table T-slot.
External Keyseat
It is less complicated to machine an external
keyseat on a milling machine than on a shaper. In
milling, it is no problem to start an external keyseat.
Simply bring the work into contact with a rotating
cutter and start cutting. You should be able to picture
in your mind how you’ll mill a straight external
keyseat with a plain milling cutter or an end mill. If
the specified length of the keyseat exceeds the length
you can obtain by milling to the desired depth, you
can move the work in the direction of the slot to get
the desired length. It should be easier to picture in
your mind how you’ll mill a Woodruff keyseat. The
secret is to select a cutter that has the same diameter
and thickness as the key.
STRAIGHT EXTERNAL KEYSEATS.—
Normally, you’ll use a plain milling cutter to mill a
straight external keyseat. You also can use a
Woodruff cutter or a two-lipped end mill.
Before you can begin milling, align the axis of the
work with the midpoint of the width of the cutter.
Figure 7-69 shows one method of alignment.
Suppose you’re going to cut a keyseat with a plain
milling cutter. First, move the work until the side of
the cutter is tangent to the circumference of the work.
With the cutter turning very slowly and before contact
is made, insert a piece of paper between the work and
the side of the cutter. Continue moving the work
toward the cutter until the paper begins to tear. When
it does, lock the graduated dial at ZERO on the saddle
feed screw. Then, lower the milling machine knee.
Use the saddle feed dial as a guide, and move the
work a distance equal to the radius of the work plus
one-half the width of the cutter. This will center the
cutter over the center line of the keyseat.
Use a similar method to align work with an end
mill. Move the work toward the cutter while you hold
a piece of paper between the rotating cutter and the
work, as shown in figure 7-70. After the paper tears,
lower the work to just below the bottom of the end
Figure 7-69.—Aligning the cutter using a paper strip. Figure 7-70.—Aligning an end mill with the work.
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