AMMCO 6000 Heavy Duty Drum/Disk Lathe - Manual (Page 15)

Note: A “scratch” cut should be no more than .001" deep. If
the “scratch” cut is too deep it will show a continuous line on
the face of the drum and the runout will not be apparent. Back
the tool bit off, stop the lathe, and check the mounting as fol-
lows:
A. Loosen the arbor nut and rotate the drum one-half turn
(180º) on the adapters.
Note: The adapters must be held to keep them from turning.
Retighten the arbor nut, turn the lathe ON, and make a second
“scratch” cut. Turn the lathe OFF.
B. If the first and second “scratch” cuts are side-by-side,
the runout is in the drum — not in the mounting.
Note: A very small amount of runout is permissible. A large
amount of runout indicates either a bent drum or an incorrect
mounting.
If the “scratch” cuts are opposite each other (180° apart), the
drum is not properly mounted. Shut the lathe OFF. Inspect the
mounting for cleanliness and the adapters for burrs, nicks, or
scratches. Check the bearing races for looseness. Remount the
drum and check again for runout. Proceed to machine the drum,
if the runout has been corrected.
9. Turn the lathe ON. Carefully advance the tool bit by hand
until it just contacts the drum surface and makes a "scratch" cut.
Hold the saddle hand wheel in this position and rotate its dial to
the (0) position. This setting will be the reference used to help
determine the reconditioned diameter of the drum.
10. Align the tool bit with the deepest groove worn in the
drum. Start the lathe and manually advance the tool bit into the
bottom of the groove until it makes a continuous cut around the
drum. Do not cut any deeper than necessary to make the cut
continuous. The depth-of-cut dial will show the approximate
amount of material that must be removed to recondition the
drum. Double the depth-of-cut reading and add the result to the
brake drum micrometer reading to find the finished diameter of
the reconditioned drum. This calculated measurement must be
compared with:
a. The maximum rebore limit (available from the
manufacturer’s specifications).
b. The measured diameter of the drum before machining to
determine the amount of material to be removed in each
pass.
11. With the lathe still running, give the saddle hand wheel
one full turn clockwise to move the tool bit away from the drum
wall. Manually position the tool bit at the inside corner of the
drum and set the desired depth of cut. Engage the feed gearbox
and set the feed speed.
Brake Lathes
AMMCO 6000, 6002 Brake Lathes • 9
Figure 4 - Drum Mounting, First “Scratch” Cut
Figure 5 - Drum Mounting, Second “Scratch” Cut