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Rotational Speed Selection; Facing A Workpiece - OTMT SC4 User Manual And Installation Manual

Bench lathe
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dial moves the tip of the tool 0.0005 (one-half
thousandth) towards the face of the workpiece.
Compound set to 30
Depending on the type of operation being
performed, the tool post usually is rotated to
bring the cutting tip of the tool into the desired
orientation with the workpiece. For example,
for a facing cut, the tool post is angled so that
the left side of the cutting tool is at a slight
angle (say 10 ) to the face of the workpiece.
For a turning cut, the tool may be at the same,
or a similar, orientation; however the cutting
would now be done by moving the tip of the
tool to the left (towards the headstock) along
the length of the workpiece.

Rotational Speed Selection

Different machining operations and materials
require different cutting speeds for optimal
results. In general, harder materials such as
stainless steel are machined at lower speeds
and softer materials such as aluminum at
higher speeds.
The important factor is the speed at which the
edge of the cutting tool passes over the
surface of the workpiece. For larger diameter
work, the tool moves over the work surface
faster than for a smaller diameter workpiece
rotating the same number of RPM. Cutting
speed also depends on the speed at which the
tool is advanced into the work, known as the
feed rate.
Similarly, when drilling holes, larger diameter
drills are used at lower RPM than smaller
diameter drills. A full discussion of the details
of cutting speeds is beyond the scope of this
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manual. Detailed information can be found in
Feeds and Speeds in Wikipedia.
While cutting speeds and feeds are critical in
industrial settings where maximum production
throughput is the goal, for the home shop and
light industrial use they are not nearly as
demanding. For most cutting operations on the
SC4 lathe a speed of between 600 and 1200
RPM will work well, with lower speeds being
used for harder materials and higher speeds
for softer materials.
Rotational speeds above 1500 RPM are used
mainly for polishing and for drilling with very
small drills. Very low speeds are used for
threading, tapping and reaming. In fact, these
operations may be performed by manually
turning the spindle using a hand crank
engaged in the left end of the spindle.

Facing a Workpiece

Facing removes material from the end, or face,
of the workpiece. When working with relatively
small diameter stock, say less than 3" diameter,
facing cuts generally are made by rotating the
cross-feed handle by hand. To face a larger
diameter workpiece the SC4 has a power
cross feed capability.
When making a facing cut, it is important to
use the carriage lock to lock the carriage to the
ways. Otherwise, the cutting force on the face
of the workpiece could cause the carriage to
move away from the end of workpiece while
the cut is being taken. If this happens, the face
will have a slight conical shape rather than
being exactly square to the centerline of the
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