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Q. I’ve been told that the gray wheels that came with my grinder will burn my woodworking tools and that white wheels are better. True?
A. The stock wheels that come with most grinders are designed for the metalworking trade. They’re way too hard for grinding the hardened steel used for chisels and plane irons. It sounds strange, but the harder the steel, the softer the bond in the wheel should be. Here’s why: Hard steel quickly dulls the abrasive particles in a wheel. With a soft bond, the dull abrasive sloughs off quickly,
leaving fresh, sharp abrasive to do the work. A hard bond, on the other
hand, holds tight to the abrasive particles, even after they’re dull.
The dull or “glazed” wheel rubs as much as it cuts, creating friction
and heat that will toast your tools. The best all-around grinding
wheel for woodworking tools is an 80-grit aluminum oxide wheel with a
relatively soft bond designated by the letter H, J or K on the wheel
label (Photo 1). An H bond is the softest and will provide the coolest
grinding. Turners tend to prefer a J grade wheel; its harder bond
resists grooving by gouges and parting tools. Smart buyers read labels.
Look for a series of numbers and letters that usually comes after the
wheel size. It’s best to be color-blind when you are buying a
new wheel (Photo 2). Instead, trust the label to give you the precise
information you need.
Look for three things on a grinding wheel label. First, the letter A,
which stands for aluminum oxide, the abrasive you’ll want. Next is the
grit size; a 60- or 80-grit wheel is best. Finally, a letter right
after the grit size represents the hardness of the bond. Letters from H
to K are considered soft bonds, with H being the softest.
Don’t let color be your guide. Aluminum oxide is made from bauxite, a
naturally white mineral that can be given any color in manufacturing.
The only way to really know what you’re getting is to read the label.
Source:
Lee Valley and Veritas, (800) 871-8158, www.leevalley.com, Grinder
wheels: 6-in. x 3/4-in. 80 grit, #08M18.02, $20, 6-in. x 1-in. 80 grit,
#08M18.01, $23, 8-in. x 1-in. 80 grit, #08M19.01, $30
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