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12
By using different abrasive types and different weights
of grit it is possible to produce a very wide variety of cutting
speeds and surface finishes on a very wide range of
materials -- from metals, to plastics, to wood.
The following information is provided as a general
guide to the types of discs appropriate to many materials.
JET supplies a variety of abrasive disc types. However,
your industrial distributor may be able to provide you with
special abrasive discs for specific production applica-
tions. And of course, your workpiece supplier should be
consulted for recommendations, as well.
Aluminum Oxide
Aluminum oxide is available in cloth backed discs
in a very wide range of grits -- typically from 24 (extremely
aggressive) to 400 (almost a polishing grade.)
Aluminum oxide is suitable for use on virtually all
materials -- ferrous and non-ferrous. The list of materi-
als appropriate for aluminum oxide cutting includes low,
medium and high carbon/alloy steels, brass, aluminum,
bronze, copper and titanium.
Garnet
Garnet is available in a cloth backed disc, typically
in a range of grits from 80 to 220.
Garnet is a material used almost exclusively on
wood. This makes it appropriate to shops such as
pattern shops. It has the beneficial property of grit
fracturing at low pressure levels. This quick renewal of
the cutting surface results in more rapid wear-out of the
disc, of course. But it also allows very low temperature
sanding of wood -- thus permitting rapid sanding without
burns. This is particularly beneficial when doing sanding
on end grains.
Silicon carbide
While discs may be available for 20 inch grinding,
this material is not recommended for use on the Model
J-4421 because a water coolant/lubricant is typically
required for effective use of this material.
Application tip
While the 20 inch grinder can mount the full range
of grits available -- from 24 to 400 -- the most efficient
production and the longest abrasive disc life can be
achieved when the production manager is aware of the
capabilities of the grits offered. If you start with a
workpiece which has been rough cut with an 80 grit
wheel of some type, and you eventually want to achieve a
finish at the 400 grit level -- don't go directly from the 80 to
the 400 disc machine. The 400 grit wheel will eventually
do the job, but it will take an excessive amount of time
and the disc will have a short service life. Plan your
surface finishing to take advantage of the full range of
grits available to the shop.
Recommended abrasives
The above illustration (Figure 11) shows how to set
and use the miter gauge to grind a simple angle on a
workpiece.
To grind a compound angle you can set the miter
gauge to one required angle and set the table tilt to a second
required angle, thus achieving the compound angle desired.
Remember: When grinding complex compound
angles, always test your table and miter set-up on scrap
material before attempting a finish machining task on the
actual piece part you will be grinding.
Push workpiece in
direction of large black
arrow to cut the angle
set on the miter gauge
Workpiece
Miter slot
Figure 11: Use of the miter system
Table
Miter gauge
Disc
Using the miter system
The miter slot in the table allows you to use a miter
gauge to grind angles on workpieces. Use the following
procedure:
1. Put the table in a level position. Use the table tilt
mechanism to adjust it, if necessary.
2. Loosen the lock knob on the miter gauge.
3. Adjust the miter gauge to the angle you want to cut.
4. Lock the lock knob on the miter gauge.
5. Put the miter gauge in its miter slot on the table.
6. Turn the grinder ON and allow the motor and disc to
come up to full speed.
7. Hold the reference edge of the workpiece against the
miter gauge face and move the workpiece into contact with
the abrasive disc.
8. Allow the workpiece to slide forward, along the face of the
miter gauge, until the required depth of cut has been
achieved.
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