Figure 9-11.--Shaping irregular surfaces.
tooth space in the form of a plain rectangular groove,
which external and internal keyways are cut to produce
then finish it with a tool ground to the tooth's finished
the greatest strength. When you cut a keyway in the
contour and size.
gear, set the downfeed micrometer collar to zero at the
To machine a rack, use the following sequence of
point where the cutting tool first touches the edge of the
hole. First, remove the crown, X, from the shaft to
produce a flat whose width is equal to the width of the
1. Clamp the work in the vise or to the table.
key. Then, make a cut in the shaft to depth 2. The
2. Position a squaring tool, which is narrower
distance of Y plus Z is equal to the height of the key that
is to lock the two parts together.
than the required tooth space, so the tool is
centered on the first tooth space to be cut.
SHAPING IRREGULAR SURFACES.--To
machine irregular surfaces, use form ground tools and
3. Set the graduated dial on the crossfeed screw
feed the cutting tool vertically by hand while using
to zero, and use it as a guide to space the teeth.
power feed to move the work horizontally. A gear rack
4. Move the toolslide down until the tool just
is an example of work you might shape by using form
tools. You can use the toolhead feed to shape work such
touches the work, and lock the graduated collar
as concave and convex surfaces. When you machine
on the toolslide feed screw.
irregular surfaces, you have to pay close attention
5. Start the machine and feed the toolslide down
because you control the cutting tool manually. Also,
slightly less than the whole depth of the tooth,
you should lay out the job before you machine it to
provide reference lines. You also should take roughing
using the graduated collar as a guide, and rough
cuts to remove excess material to within 1/16 inch of
out the first tooth space.
the layout lines.
6. Raise the tool to clear the work and move the
You can cut RACK TEETH on a shaper as well as
crossfeed a distance equal to the linear pitch of
on a planer or a milling machine. During the machining
the rack tooth by turning the crossfeed lever.
operation, you may either hold the work in the vise or
Rough out the second tooth space, and repeat
clamp it directly to the worktable. After you mount and
position the work, use a roughing tool to rough out the
this operation until all spaces are roughed out.