Page 201 - Machinery Component Maintenance

Machinery Alignment 183

2. If used on a sleeve bearing machine, axial float error may occur.
One method of avoiding this is to bump the turned shaft against the
axial stop each time before reading. Another way is to use a second
face indicator 180" around from the first, and take half the alge-
braic difference of the two face readings after 180" rotation from
zero start. Figure 5-10 illustrates this alignment method. Two 2411.
tubular graphite jigs are used for light weight and high rigidity.
3. If used with jigs and posts, two or three axis leveling is required,
for ball and sleeve bearing machines respectively. Reverse-indica-
tor requires leveling in one less axis for each.
4. Face-and-rim has lower geometric accuracy than reverse-indicator,
for spans exceeding coupling or jig diameter.
5. Face sag is often insignificant, but it can occur on some setups, and
result in errors if not accounted for. Calibration for face sag is con-
siderably more complex than for rim sag.
6. For long spans, face-and-rim jigs are usually custom-built brackets
requiring spacer removal to permit face mounting. Long-span re-
verse-indicator jigs, by contrast, are available in adjustable clamp-
on models not requiring spacer removal.
7. Graphing the results of face-and-rim measurements is more com-
plex than with reverse-indicator measurements.

Figure 5-10. Face-and-rim indicator setup using lightweight, high-rigidity tubular graphite
fiber-reinforced epoxy jigs.