13
8. Inspect the new grinding wheel and perform a
“ring test” (
sect. 9.1
). Do not install a damaged
wheel.
9. Install inner flange, wheel (E), outer flange (D)
and nut (C) on the shaft. Tighten nut.
Do not overtighten nut; this
may cause wheel to crack. Maximum safe torque
on nut is 20 lbf•ft (270 kgf•cm).
10. Reinstall guard cover. Adjust spark guard and
tool rest to 1/16" clearance from wheel.
9.4
Wheel balancing
With the grinder
unplugged from the power
source
, and the arbor nut snugged down, rotate
wheel by hand and observe its motion.
A grinding wheel has proper balance when:
1. The wheel’s outside face spins true and round;
that is, its circumference rotates concentric to
the arbor.
2. There is no side-to-side wobble.
The operator who takes time to patiently perform
needed adjustments will be rewarded by a wheel
running true, and accurate grinding of work pieces.
9.4.1
Adjusting concentricity
If the outside face is not rotating concentric to arbor,
try shifting the wheel closer to arbor centerline
before tightening the nut.
Another method of achieving concentricity is the use
of a wheel dresser. “Dressing” is the removal of the
current layer of abrasive to expose a fresh surface.
A wheel dresser is also used to “true” a wheel; that
is, to make the grinding surface parallel to the tool
rest, so the entire wheel face presents an even
surface to the work piece. Proper use of a wheel
dresser will eliminate high spots and result in
concentric rotation about the arbor, as well as
minimize vibration. See
sect. 9.5
.
9.4.2
Correcting side-to-side wobble
The JBG-W Grinder has large, machined flanges,
making wobble unlikely if a good quality grinding
wheel is used. Should a wheel exhibit need for
adjustment:
1. Loosen nut and rotate outer flange a small
amount. Snug the nut and spin the wheel by
hand to check.
2. If wobble still exists, continue repeating step 1,
rotating outer flange incrementally in the same
direction. See Figure 9-2. Make sure to keep
the wheel in same position each time.
3. If complete rotation of outer flange has proved
ineffective, remove nut, outer flange, and wheel
(keep wheel in same orientation by placing a
pencil mark somewhere on it for reference).
Then rotate inner flange about 90° and repeat
the above steps for outer flange.
4. Continue this combination of flange movements
until the wobble is eliminated.
If required, a shim made of paper or card stock may
be placed between flange and wheel.
Figure 9-2: wheel balancing
NOTE: Very slight wobble may still exist at spin-up
and spin-down, but will not affect normal speed
operation.
9.5
Dressing the wheels
Below is a general procedure for dressing a grinding
wheel. Always consult the wheel dresser
manufacturer’s instructions for specific information
pertaining to the tool.
Use safety glasses or face
shield during dressing operations.
1. Back off the tool rest enough to allow the
dresser to hook over its inside edge (see Figure
9-3). Tighten tool rest in position.
2. Turn on grinder and allow it to reach operating
speed.
3. Set wheel dresser on tool rest and bring it into
contact with wheel by raising its handle. Hold
the dresser firmly.
Note:
If sparks appear, increase the pressure
of the dresser discs against the wheel.
4. Move dresser evenly left and right across wheel
face until wheel looks clean and is square to tool
rest.
5. Remove dresser, and adjust tool rest to 1/16”
away from the newly dressed wheel.
