Festool RO 125 FEQ Plus Supplemental User's Manual - page 16
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Rotex Series Dual Mode Sanders
Sanding Techniques
Establishing Optimal Sanding Pressure
The amount of downward force applied to the sander will
have a varying impact on how aggressive the sander will
perform, but also on the controllability and finish level too.
More downward force will make the sander operate more
aggressively, but it will also tend to make the sander more
difficult to control and reduce the quality of the finish. The
general rule for any rotational type sander is to keep mini-
mal downward force on the sander and let the sander to the
work on its own.
The primary sign that you are applying too much down
pressure is that the sander will lurch and jitter as it moves
across the sanding surface. When this happens, reduce the
sanding pressure, which even includes lifting the sander a
little bit when necessary.
In random orbit mode, anything that diminishes the “ran-
domness” of the pad rotation increases the occurrence of
visible scratches. Initial intuition may suggest that slowing
down the pad rotation is good, but the opposite is true.
If the pad is not freely spinning, then the motion is not
random, and too much down force is being applied to the
sander.
In Rotex mode, by their nature, the sanders will be more
difficult to control because different parts of the sanding pad
will be operating in a cross-grain direction at different times.
This is what give the sander its rapid material removal rate.
So in Rotex mode, the sander will expectably have more
jitter, especially with coarser grits.
NOTE: The effect of the vacuum created below the
sanding pad from the dust extractor will add some
downward force to the sander. It is important to
reduce the power of the dust extractor so it is not
applying too much down-force on the sander.
Sanding Pattern and Movement
One key to achieving a quality sanded finish is to establish
an effective and smooth sanding pattern for moving the
sander across the workpiece. Different patterns and speeds
of motion will be optimal for different material types and
even different grits of sand paper.
Because the sanding pad is moving in a clockwise dual
motion (both in Rotex and random orbit modes), a general
clockwise sanding pattern produces the least resistance to
movement, and therefore, the smoothest pattern. As much
as possible, make your motions and direction changes in a
general clockwise direction.
For homogenous materials that do not have a discernible
grain direction, such as metals, plastics, solid surface, and
finishes; a circular pattern may be best. These types of pat-
terns do not have a stopping or sharp transition point where
the direction of the sander is abruptly changed.
For materials with an inherent grain structure such as wood
and even some plastics, the sander motion should be kept
generally in-line with the grain as much as reasonably pos-
sible. This leads to a linear back and forth motion, but the
transitions for changing direction should be as smooth as
possible without an abrupt stop/start.
Example, Solid Surface Joint Leveling:
Solid surface material has a non-oriented grain structure. It
is therefore best to sand in a generally circular pattern. For
initial leveling, sanding emphasis should be applied to the
higher of the two surfaces, but not to the complete exclu-
sion of both surfaces. This calls for an oval pattern over-
lapping onto the lower surface, yet focused on the upper
surface.
As the joint becomes more level, the pattern should switch
to perpendicular to the joint in tight overlapping loops.
Example, Wood Panel Joint Leveling:
In a similar fashion, initial leveling should focus on the
higher surface, but not to the exclusion of the lower surface.
Some overlap across the joint is required to avoid the likeli-
hood of creating a slight depression on the high surface just
inside the joint. As leveling progresses, the sanding pattern
should become more balanced across the two pieces.