Alignment Methods

Why do you still want to stuff around with dial indicators? Go for laser alighnment techniques. This is 2009 almost 2010. it is much faster and accurate to use a laser. (Time is money)

Sorry dear i disagree with you could you identify soft foot in laser alignment?

choosing the alignment method is based on the accessible space(Distance piece length) between the driver and driven coupling flanges.

Rim and Face Method is usually used for small distance leg while the Reverse Indicator Method is used for larger distances for ex. in our project 300 mm distance is the limit for switching of one method to the other one.below is some tips for the method of alignment from referenced books

BLOCH, H. P. (1996). Major Process Equipment Maintenance and Repair Vol4 (2nd ed.)

Page 17:

Machinery Alignment

1. The owner should insist that the installing agency use the reverse
indicator method of alignment, or the laser alignment method.
whenever the separation between shaft ends is larger than 50 percent
of the diameter at which the dial indicators contact the coupling
rim. The advantages of using this system far outweigh the
arguments for rim-and-face and other mechanical alignment methods.

and here are some ads&pros of Rim and Face method vs Reverse indicator method from :

BLOCH, H. P. (1990). Machinery Component Maintenance and Repair Vol3 (2nd ed.)

Reverse-Indicator Method
This is the setup we prefer for most alignment work. it has several advantages:
1. Accuracy is not affected by axial movement of shafts in sleeve
bearings.
2. Both shafts turn together, either coupled or with match marks, so
coupling eccentricity and surface irregularities do not reduce accuracy

of alignment readings.

3. Face alignment, if desired, can be derived quite easily without direct
measurement.
4. Rim measurements are easy to calibrate for bracket sag. Face sag,
by contrast, is considerably more complex to measure.
5. Geometric accuracy is usually better with reverse-indicator
method in process plants, where most couplings have spacers.
6. With suitable clamp-on jigs, the reverse-indicator method can be
used quite easily for measuring without disconnecting the coupling
or removing its spacer. This saves time, and for gear couplings,
reduces the chance for lubricant contamination.
7. For the more complex alignment situations, where thermal growth
and/or multi-element trains are involved, reverse-indicator can be
used quite readily to draw graphical plots showing alignment conditions
and moves. It is also useful for calculating optimum moves
of two or more machine elements, when physical limits do not allow
full correction to be made by moving a single element.
8. When used with jigs and posts, single-axis leveling is sufficient
for ball-bearing machines, and two-axis leveling will suffice for

sleeve-bearing machines.

There are some limitations of the reverse-indicator method. It should
not be used on close-coupled installations, unless jigs can be attached behind
the couplings to extend the span to 3 in. or more. Failure to observe
this limitation will usually result in calculated moves which overcorrect
for the misalignment.
Both coupled shafts must be rotatable, preferably by hand, and preferably
while coupled together. If only one shaft can be rotated, or if neither
can be rotated, the reverse-indicator method cannot be used.
If the coupling diameter exceeds available axial measurement span,
geometric accuracy will be poorer with reverse-indicator than with faceand-
rim.
If required span exceeds jig span capability, either get a bigger jig or
change to a different measurement setup such as face-face-distance.
Cooling tower drives would be an example of this.

Face-and-Rim Method

This is the "traditional" setup which is probably the most popular, although
it is losing favor as more people learn about reverse-indicator.
Advantages of face-and-rim:
1. It can be used on large, heavy machines whose shafts cannot be
turned.
2. It has better geometric accuracy than reverse-indicator, for large diameter
couplings with short spans.
3. It is easier to apply on short-span and small machines than is reverse-
indicator, and will often give better accuracy.
Limitations of face-and-rim:
1. If used on a machine in which one or both shafts cannot be turned,
some runout error may occur, due to shaft or coupling eccentricity.
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 1800 around from the first, and take half the algebraic
difference of the two face readings after 1800 rotation from
zero start. Figure 5-10 illustrates this alignment method. Two 2-in.
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-indicator
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 considerably
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 reverse-
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 complex
than with reverse-indicator measurements.

for detailed information you have to have a look on mentioned book.