Two spacers totaling 0.040"
A pair of two shims will do the job. After finding
a combination that's just right, write the
required thickness on a piece of masking tape
stuck to the tool; then you'll know what shims
to use next time you use that tool. Over time,
as the tool is sharpened, metal is removed
from the top surface of the cutting edge, thus
lowering the height of the tool and reducing the
thickness of shims required.
Quick Change Tool Posts
Due to the time-consuming nature of setting
tool heights using shims, experienced lathe
users generally invest in a Quick Change Tool
Post (QCTP). A QCTP uses a separate holder,
with an adjustable height feature, for each tool.
The proper height for each tool can quickly be
set using a thumbscrew and, once set, ensures
that the tool is at the correct height any time it
is used in the holder. Therefore, tools can be
changed in a matter of a few seconds.
Positioning the Tool
Mount the tool bit in the tool holder so that the
tip extends no more than about ½" from the
edge of the tool holder. The objective is for the
tool to be as rigid as possible and to avoid
overhang that could cause flexing of the tool
holder that can result in chatter. Chatter is a
squealing or screeching sound from the tool
that indicates that vibrations are occurring.
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Chatter will cause uneven variations in the
surface of the workpiece which often are
visible upon inspection. For the same reason
the compound slide should be extended no
more than necessary. The farther back it sits
over the center of the compound, the more
rigid is the setup.
Tool positioned for a facing cut
The tool bit should be approximately centered
under the clamping screws of the tool holder.
For a 2-½" long tool bit, only two clamping
screws are used to hold the bit. The shims
under the tool bit should not extend out much
beyond the edge of the base of the tool holder.
Tool bit height adjusted by shims
For the following exercises, the compound
should be set to an angle of 30 as indicated
by the protractor scale at the reference mark
on the left side of the compound base plate.
This angle is not critical, and with experience
each lathe operator tends to develop their own
preferences regarding the setting of the angle.
angle is convenient because each
division that the compound is advanced on its