Chapter 8 Power Tools 215
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onto the fl at base of the sander. Sheet sanders have a motor that moves the
sanding pad in a circular motion at high speed.
The motion of a random orbital sander is similar, except that the random
orbit mechanism has an offset drive bearing that also moves the pad in an
elliptical pattern. When these two motions are combined, the pad of the
random orbital sander moves in a randomized manner. This reduces the tiny
circular swirl marks that a standard sheet sander tends to leave behind.
To combat the swirls left behind by a sheet sander (particularly when
moving against the grain), the operator must keep the sander moving,
working as much with the grain as possible. Using progressively fi ner grits of
sandpaper with each step of the sanding process will remove the swirls left
by the previous sanding. Final sanding by hand may be required for really
fi ne fi nishes.
Detail Sanders
Some surfaces are too small or are located behind obstructions that
prevent the use of sheet or random orbital sanders. Detail sanders that are
designed for use on wood have a triangular sanding pad that is smaller than
the standard 1/4 sheet sanders, Figure 8-49C. These sanding pads have an
orbital drive system like sheet sanders, and the sandpaper is also attached
using a hook-and-loop system or adhesive. Another type of detail sander,
often used in auto body work, is actually a small disk sander that uses a 2″
diameter or less sanding attachment. When using these tiny disk sanders,
keep the tool moving; allowing it to remain in one position too long can burn
the surface from the concentrated friction.
Stationary Sanders
Stationary sanders work like portable sanders
except the workpiece is brought to the larger, more
powerful machine. Most stationary sanders include
a support table that functions much the same as the
tool rest on the bench grinder, Figure 8-50. It can be
adjusted for producing angles as long as the clearance
between the sanding surface and the table is kept to a
minimum of 1/8″. Care must be taken to hold the work
in a manner in which the action of the sander draws
the work toward the support table and not toward
the operator.
Abrasives
Many different materials are used as abrasives,
including naturally occurring materials such as fl int
and garnet, and other substances such as aluminum
oxide, silicon carbide, ceramic, diamond, and cubic
boron nitride. It is interesting to note that there is no sand in sandpaper. The
synthetic materials used are more consistent in grain size and last longer than
naturally occurring sand.
Andresr/Shutterstock.com
Figure 8-50. This stationary disc sander is equipped
with a table that supports the workpiece while it is
being sanded.