Festool RO 125 FEQ Plus Supplemental User's Manual - page 8
8
Rotex Series Dual Mode Sanders
Anatomy of Sandpaper
The various parts of sandpaper affect its performance.
These are shown below and explained in the subsequent
sections.
StickFix
Backing
Base
Bond
Top
Bond
Abrasive
Grit
Dispersion
StickFix is a short-nap hook and loop system for retaining
the sandpaper to the Festool sanding pad. The stiff, short-
nap hooks resist heating effects, and therefore last longer.
Backing is the primary substrate for the sandpaper. The
backing type determines the performance and longevity of
the sandpaper. Stiffer backings resist the pressure of the
individual grit particles, and is therefore more aggressive in
sanding. Softer backings conform to the grit particles more,
so the result is shallower scratches from the grit particles.
Paper backing is the most common and economical type,
and comes in different thicknesses designated by a letter-
weight of b, c, d, or e with the higher the letter, the heavier/
stiffer the paper.
Cloth backed disks are the stiffest and intended for extreme
usage conditions where long-life is important. The extra
durability makes them ideal for a metal working environ-
ment, but they may also be used for aggressive sanding in
woodworking.
Foam backed disks provide the softest backing for the shal-
lowest scratches. This permits the disk to better contour to
the surface being sanded and is ideal for polishing.
Abrasive is the material that performs the actual sanding
or abrasion. The two most common types of abrasive mate-
rial are aluminum oxide and silicon carbide, with aluminum
oxide being the more common of the two.
Silicon carbide is a very hard material with very sharp
edges. Because silicone carbide is so hard, it fractures
easily, and this exposes new cutting edges to the sanding
operation. This keeps the sandpaper very sharp for cutting
hard materials, but the grit gets smaller with usage. A side
benefit of this is that a coarse grit sandpaper will become
a finer grit with use, which is typically desired in the sand-
ing process. Silicon carbide is best suited for finish sanding
where reduced sanding pressure reduces how frequently the
grit cleaves.
Aluminum oxide is almost as hard as silicon carbide, but the
crystals are pyramid shaped and do not cleave the edges
during use. The edges aren’t as sharp, but that is what
permits them to last longer. This long life is the reason alu-
minum oxide is one of the most common abrasive materials.
Grit is the size of the abrasive particles. The smaller the grit
number, the larger the grit particle size. Larger grit particles
will cut deeper into the sanded surface, and therefore, more
aggressively. However, the deeper the cut, the deeper the
scratches. This is the reason why sanding is performed with
progressively finer grits; to remove the scratches left behind
from the coarser grits.
Dispersion (Coat) is the spacing between grit particles
that coat the substrate. The term “open coat” for example,
means that at least 70% of the substrate is open or
uncoated. A closed coating means that the substrate is
nearly fully coated, and a semi-open coat falls somewhere
in between the two. The dispersion is most noticeable in the
coarser grits where an open coat results in visible exposure
of the substrate (see image below).
A more open dispersion leaves more room for sanding dust
(called swarf) to clear the sanding grit to avoid buildup and
clogging, but also permits the grit to penetrate deeper into
the sanded workpiece, leaving deeper scratches.
Open Coat
Sandpaper
Base Bond and Top Bond is the material and/or method
for adhering the abrasive to the backing material. The grit
material is impregnated into the bonding agent to slightly
encapsulate the grit material for better adhesion and less
fracturing of the grit.
The thickness of the top
bond is called the level-
ing, as it tends to fill in
the valleys and level the
bond coating. An open
leveled top bond is lighter
and leaves deeper valleys
to permit greater swarf
removal.
A closed leveled top bond
is thicker and fills in the
valleys, but provides
a stronger bond of the
abrasive grit particles.
The prevents the grit from
breaking loose from the
substrate for longer last-
ing, durable abrasive prop-
erties, but may clog faster
when sanding materials
that generate more swarf.
Open
Leveled
Closed
Leveled