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10
Table
Disc
Rotation
Safest and most
effective work area
Safest and most
effective workpiece
positioning is where
abrasive force of
rotating disc tends to
hold piece on the table
Figure 6: Correct table work area
Applying a workpiece to the
disc face
No matter what size, type or material workpiece you
will be grinding, there are several important consider-
ations you must understand if you are going to use the
Model J-4421 disc grinder effectively.
1. Always be certain the wheel guard is positioned
over the disc edge. Materials abraded from your
workpiece will be hurled off the wheel if the wheel guard
is not in position.
2. Always allow time for the disc to come fully up to
motor speed before contacting the workpiece to the disc.
This gives you a chance to check for possible wheel
wobble (looseness of the disc or motor, or damage from
some earlier operation) before working against the disc.
3. This is a very powerful and aggressive grinding
device which operates at high surface speeds. There-
fore, you always want to support the workpiece while
using the work table. "Freehand" presentation of a
workpiece to the disc surface is risky to you, to the
workpiece, and to bystanders. It is not possible to over
emphasize the need to keep the workpiece firmly on the
table!
4. The safest position at which to do any grinding
is on the righthand side of the work table where the disc
is moving downward past the work table. Whenever
possible, keep the workpiece in this area when grinding.
In addition to safety, keeping the workpiece in this area
greatly increases the effectiveness of the dust control
chute and any vacuum dust control system you might be
using. See Figure 6.
5. The speed and aggressiveness of the machine
means that CONTROL of the workpiece, by you, is
absolutely essential. ALWAYS USE TWO HANDS to
control the workpiece.
6. Because of the speed with which the disc can
grind, heat build-up on work pieces is usually very rapid.
To prevent burns and/or possible loss of control of any
workpiece:
a. Use heat resistant gloves to hold any workpiece.
b. Where possible and appropriate, use additional
tooling or fixturing to hold the workpiece when pressing
against the grinding disc.
ON/OFF Switch
The ON/OFF switch is located on a post on the left
hand side of the grinder. There are two push buttons on the
switch: RED is for OFF and BLACK is for ON. See Figure
7.
The switch is a Low Voltage Protection or LVP switch.
When line voltage drops below a safe working voltage (due
to start-up of larger machines on the electrical branch or
other fluctuations in line voltage) the switch automatically
trips OFF.
The purpose of this feature is to prevent accidental re-
starts and damage to any workpieces you might be grinding.
To restart the machine you should remove the
workpiece from the table and turn the switch ON, again.
Then wait for the motor to come up to full speed before
continuing your grinding.
Figure 7: ON/OFF switch
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