coarse-grain wheels to remove a large amount of
DIAMOND WHEELS
material (except on very hard materials). If you need
a good finish, use a fine grain wheel. If the machine
Diamond grinding wheels are classed by
you are using is worn, you may need to use a harder
themselves. They can be made from natural or
manufactured diamonds, and they are very expensive.
grade wheel to offset the effects of that wear. You
Their cutting speeds range from 4,500 to 6,000
also can use harder grade wheel if you use a coolant
surface feet per minute. Use them with care and only
with it. Refer to your machine's operators manual to
to grind carbide cutting tools. They are marked
select grinding wheels for various operations.
similarly to aluminum-oxide and silicon-carbide
Figure 5-6 shows the type of grinding wheel used
wheels, although there is not a standard system. The
on bench and pedestal grinders. When you replace
usual diamond abrasive wheel identification system
the wheel, be sure the physical dimensions of the new
uses seven stations as follows:
wheel are correct for the grinder. Check the outside
1. Type of abrasive, designated D for natural and
diameter, the thickness, and the spindle hole. If
SD for manufactured.
necessary, use an adapter (bushing) to decrease the
size of the spindle hole so it fits your grinder.
2. Grit size, which can range from 24 to 500. A
100-grain size might be used for rough work,
You should use A3605V (coarse) and A60M5V
and a 220 for finish work. In a Navy machine
(fine or finish) wheels to grind or sharpen single point
shop, you might find a 150-grain wheel and
tool bits such as those for a lathe, planer, or shaper
use it for both rough and finish grinding.
made from high-carbon or high-speed steel. Use an
A46N5V wheel for stellite tools. These wheels have
3. Grade, designated by letters of the alphabet.
aluminum oxide as an abrasive material; use them to
4. Concentration, designated by numbers. The
grind steel and steel alloys only. If you use them on
concentration, or proportion of diamonds to
cast iron, nonferrous metal, or nonmetallic materials,
bond, might be numbered 25, 50, 75, or 100,
you may load or pin the wheel when particles of the
going from low to high.
material are imbedded in the wheel's pores. This
strains the wheel and could cause it to fail and
5. Bond type, designated B for resinoid, M for
possibly injure someone.
metal, and V for vitrified.
6. Bond modification (This station may or may
WHEEL INSTALLATION
not be used).
You must install the wheel of a bench or pedestal
7. Depth of the diamond section. This is the
grinder properly or it will not operate properly and
thickness of the abrasive layer and ranges
may cause accidents. Before you install a wheel,
from 1/32 to 1/4 inch. Cutting speeds range
inspect it for visible defects and "sound" it to learn if
from 4,500 to 6,000 surface feet per minute.
it has invisible cracks.
GRINDING WHEEL SELECTION
To sound a wheel, hold it up by placing a hammer
AND USE
handle or a short piece of cord through the spindle
hole. Use a nonmetallic object such as a screwdriver
You should select a grinding wheel that has the
handle or small wooden mallet to tap the wheel lightly
proper abrasive, grain, grade, and bond for the job.
on its side. Rotate the wheel 1/4 of a turn (90) and
Base your selection on such factors as the physical
repeat the test. A good wheel will give out a clear
properties of the material to be ground, the amount of
ringing sound. If you hear a dull thud, the wheel is
stock to be removed (depth of cut), the wheel speed
cracked and should not be used.
and work speed, and the finish required.
To grind carbon and alloy steel, high-speed steel,
cast alloys and malleable iron, you probably should
use an aluminum oxide wheel. Silicon carbide is the
most suitable for nonferrous metals, nonmetallic
materials, and cemented carbides.
Generally, you'll choose coarser grain wheels to
Figure 5-6.--Grinding wheel for bench and pedestal grinders.
grind softer and more ductile materials. Also use
5-5
