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November 2003 - Cutting Edge (part
2) |
FINER POINTS
 Apart
from the manufacturer’s name, grit size (the number of
teeth per square inch) is about the only information consistently
found on the back of sandpaper sheets. There are three commonly
used abrasive grading systems in Canada. The Coated Abrasives
Manufacturer’s Institute (CAMI) regulates the U.S. standard
scale. These products simply have numbers, such as 80, 120 or
320, printed on them. The Federation of European Producers Association
(FEPA), or European scale, uses the letter “P” in
front of the grit size (as in P1000). Some manufacturers offer
the micron grade scale, which has the Greek letter µ (micron
symbol) after the number (as in 320µ) and are best suited
for jobs in which a highly polished surface is desired, such
as working with metal and in sharpening applications. Factors
such as the type of backing material, the weight, the type of
abrasive material and whether the sandpaper is stearated, open
or closed coat, do contribute to the sandpaper’s performance
but may not be indicated on sandpaper sheets.
CLOG STOPPER
 The
spaces between grit particles are like the gullets of a saw
blade: the grit can’t remove wood when the spaces are
full. However, if you use a power sander, you can get extra
life out of your discs and belts. When your sandpaper is loaded,
simply offer a block of crepe rubber, such as the Veritas sanding
block (Lee Valley Tools, $9), to the rotating belt or disc and
apply light, firm pressure. Discs will become considerably cleaner
after a few moments as the block strips out accumulated dust
and fibre.
| ABRASIVE
ACTION |
ALUMINUM OXIDE
(Man-made) |
Properties: Not as sharp as silicon
carbide, but lasts longer. Hard grained. High degree of
friability (i.e., it fragments under heat and pressure,
creating new sharp edges)
Application: A good all-rounder. Works well for power
sanding wood or metal. Finer grits can be used in sharpening
applications and for finishing metals, wood and other
high-tensile- strength materials without excessive fracturing
or shedding |
ALUMINA ZIRKONIA
(Man-made) |
Properties:
An alloy of aluminum oxide and zirconium oxide. Zirconium
is a very dense, friable material, which gives this sandpaper
long life on heavy stock-removal operations. Sharp, hard
and durable. Cuts faster and lasts longer than aluminum
oxide, but not as long as ceramic.
Application: Used mostly on belts and discs for machine
sanding. Works well on stainless steel, titanium and other
hard steels. Can also be used on wood |
CERAMIC
(Man-made) |
Properties: More durable and expensive
than other abrasives. Often bonded with aluminum oxide.
Application: Used primarily on belts and discs for
power sanding. Generally available in lower grits for
shaping and levelling wood |
EMERY
(Natural) |
Properties:
Very soft. Usually comes on flexible cloth backing. (Cloth
backings are the stiffest and produce the coarsest and
fastest cut)
Application: Excellent for sanding and polishing metal.
Good for rust removal, polishing, deburring, and corrosion
and paint removal |
GARNET
(Natural) |
Properties: Garnet is soft and
dulls quickly compared to man-made abrasives, but cuts
smoother than other abrasives
Application: Suitable for sanding bare wood. Excellent
for final sanding before applying a finish |
SILICON CARBIDE
(Man-made) |
Properties: Extremely
hard and sharp, but wears quickly
Application: Suitable for cutting harder materials,
such as paint, fibreglass and plastic. Best for smoothing
joint compound and removing dust nibs between coats of
finish. Extra-fine grits can be used for sanding the final
finish coat |
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