For the exercises in the following sections of
this manual we will use a single HSS tool bit
with an easily formed shape that be used both
for facing and turning operations. The tool was
ground on a bench grinder from a 5/16" square
x 2 ½" long tool blank.
Note that the sides of the tool bit near the
cutting tip are undercut to provide clearance.
Without sufficient clearance, or "relief", the
edges of the tool will rub against the workpiece
without proper cutting action.
Setting the Tool Height
For proper cutting action the top edge of the
cutting tool must be aligned with the centerline
of the lathe. If the tip of the tool is higher or
lower than the centerline, it will tend to rub
against or dig into the workpiece rather than
On a facing operation, if the tip of the tool is
too high or too low a small nub of material will
be left at the center of the face: usually a
tapered cone shape if the tool is too high and a
narrow cylinder if the tool is too low. If the tool
tip is too high, resistance usually will be felt in
the cross-slide handle as the tip of the tool
approaches the center of the workpiece. These
effects make a facing operation a convenient
way to check the height of the cutting tool.
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Cutting tool tip
The height of the cutting tool is adjusted by
inserting shims underneath the tool. A set of
automotive feeler gages that can be removed
from their holder makes a convenient set of
shims for this purpose.
Another method for setting the tool height is to
align the tip of the cutting tool with the point of
a dead center mounted in the tailstock. Insert a
dead center into the tailstock ram to act as a
reference for the lathe centerline.
Adjust the toolholder so that the tip of the
cutting tool is near the tip of the dead center,
then select shims of various thickness and
stack them underneath the base of the cutting
tool until the tip of the cutting tool is at the
same height as the tip of the dead center.
Then firmly tighten the hold-down screws to
lock the cutting tool in place.