Chapter 8 Power Tools 211
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• Keep the tool in constant motion to reduce digging in and heat buildup.
• The outside perimeter of the attachment spins at a faster rpm than
areas toward the center. The result is that the most effective grinding,
or fastest removal of material, occurs at the edge. Holding the disc
fl at on a surface results in less material removal and a fl atter surface
texture, but it typically leaves swirl marks on the surface.
• Wait for the disc to stop spinning when fi nished with the grinder, and
place the machine on the work table with the disc facing up.
Bench Grinders
Bench grinders are stationary tools mounted to a workbench or table,
Figure 8-45. Pedestal grinders are usually mounted to a stand called a
pedestal that is securely affi xed to the fl oor. Bench grinders are useful for
shaping, cleaning, and polishing small metal parts. They may also be used to
sharpen and recondition tools.
Bench and pedestal grinders are often set up with a coarse abrasive
wheel on one side (for rapid removal of material), and a fi ner abrasive wheel
(for fi nishing) on the other side. They may also be equipped with wire
brushes for cleaning parts, or with soft buffi ng wheels for polishing. In most
applications, the grinding stones are enclosed, with only the actual working
area exposed. Many bench and pedestal grinders have built-in containers
for water that is used to keep parts cool as they are being shaped. This is
particularly important when sharpening tools to maintain the edge-holding
characteristics of tool steel. Allowing tool steel to change color due to heat
generated by the grinding process causes a change in the molecular structure
of the steel and results in a loss of hardness.
The following rules and the power tool safety precautions apply to
working with bench grinders:
• Adjust eye shields for a clear view of the grinding area.
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Figure 8-45. Some stationary grinders are designed to be mounted directly to a workbench.
Other models are mounted on a dedicated pedestal.