Figure 7-13.--Detail of brush rigging with sandpaper in position.
thoroughly clean the commutator and windings to
AU brush holders should be the same distance from
remove all carbon dust.
the commutator, not more than one-eighth inch, nor less
than one-sixteenth inch. A brush holder must be free of
The use of a brush seater will further improve the
all burrs that might interfere with the free movement of
fit obtained by sanding. A brush seater consists of a
the brush in the holder. Burrs are easily removed with
mildly abrasive material loosely bonded into a stick
a fine tile.
about 5 inches long. To use a brush seater to seat the
brushes, install the brushes in the brush holders and start
the machine. Press a brush securely against the
commutator by using a stick of insulating material or by
increasing the brush spring tension to its maximum
Accurate seating of the brushes must be ensured
value. Touch the brush seater lightly to the commutator,
where their surfaces contact the commutator.
exactly at the heel of the brush (fig. 7-14), so that
Sandpaper and a brush seater are the best tools to
abrasive material worn from the brush seater will be
accomplish a true seat (fig. 7-12).
carried under the brush. You must hold the brush seater
Disconnect all power from the machine. You must
behind each brush, applying the seater for a second or
take every precaution to ensure that the machine will not
two, depending on brush size. Do not hold the seater
be inadvertently started before using sandpaper to seat
steadily against the commutator because it will wear
away too rapidly and produce too much dust. After
Lift the brushes to be fitted and insert (sand side up)
a strip of fine sandpaper (No. 1), about the width of the
commutator, between the brushes and the commutator.
With the sandpaper held tightly against the commutator
surface to conform with the curvature and the brushes
held down by normal spring pressure, pull the sandpaper
in the direction of normal rotation of the machine (fig.
7-13). When returning the sandpaper for another pull,
lift the brushes. Repeat this operation until the seat of
the brush is accurate. Always finish with a finer grade
of sandpaper (No. 0). You need a vacuum cleaner for
Figure 7-14.--Using the brush seater.
removing dust while sanding. After sanding,