12 • Snap-on
Brake Lathes
Figure 14
8.
Turn the lathe ON. Turn the drum slide handwheel
clockwise until the tool bit is centered over the rust
ridge. Turn the end knob of the micrometer clockwise
until the tool bit lightly contacts the rust ridge.
9.
Turn the drum slide handwheel clockwise until
tool bit is 1/8" outside drum. Turn the end knob of the
micrometer clockwise to move the tool bit .002"
toward the rust ridge.
10.
Turn the drum slide handwheel counerclock-
wise to move the tool bit about 1/4" inside the worn
brake surface.
11.
If the tool bit is not in contact with the brake
surface, repeat steps 9 and 10 until very light contact
is made with the brake surface.
12.
Turn the drum slide handwheel counterclock-
wise until the tool bit is about 1/4" away from the
shoulder (unworn portion of the brake surface) at the
bottom of the drum.
Note:
If the cut becomes heavier as the tool bit
moves into the drum, turn the end knob of the
micrometer counterclockwise to withdraw the tool bit
slightly to maintain only light contact.
13.
Machine the shoulder away by slowly turning
the drum slide handwheel counterclockwise until the
tool bit contacts the bottom of the drum making a
“scraping” sound. Turn the drum slide handwheel
clockwise until the “scraping” stops.
14.
Hold the end knob of the tool bar micrometer
still, and turn the inner dial to zero.
Note:
Drum—depth-of-cut is determined by the con-
dition of the drum:
Ovality
Flatness (taper, bellmouth, barrel shape)
Scoring
Diameter (how close to the max. machining limit)
Cuts may be .002"—.010" deep. A rough cut
should be no more than .010", a finish cut should
be no less than .002".
A cut of .002" from an 8" drum will result in a
refinished diameter of 8.004".
Note:
A round, smooth, flat drum may require only a
finish cut .002"—.004" deep.
15.
Turn the end knob of the tool bar micrometer
clockwise to set the tool bit to the desired depth-of-
cut (not more than .010" deep).
16.
Tighten the engagement knob in the center of
the drum slide handwheel, to engage the drum slide
feed. When the tool bit has cleared the outer edge of
the brake surface, loosen the engagement knob to
stop the feed.
Figure 15
17.
Turn the lathe OFF to inspect the drum.
18.
If the first cut has not cleaned the entire brake
surface, leave the tool bar locked in position. Turn the
lathe ON. Slowly turn the drum slide handwheel coun-
terclockwise to move the tool bit into the drum mak-
ing a “scraping” sound. Turn the drum slide
handwheel clockwise until the “scraping” stops.
19.
Repeat steps 15, 16, 17, and 18.
