13
Coupling
Offset
Shaft
Dogleg
Generator
Shaft
Coupling
Turbine
Shaft
Figure 13.--Dogleg and offset.
generator or turbine shafts are assumed to be straight and any angular misalignment is assumed
to be in the coupling. In most cases this is true, but in some cases, the generator or turbine shaft
is not straight. The shaft is considered straight when no point varies more than 0.003 inch from a
straight line joining the top and bottom reading points. Nothing is normally done to correct
dogleg or offset unless it is large enough to significantly affect the static runout. If necessary,
dogleg can be corrected by shimming the coupling. Offset is rarely large enough to cause a
problem and usually can be corrected only by remachining the coupling flanges and reboring the
coupling bolt holes.
to be in the coupling. In most cases this is true, but in some cases, the generator or turbine shaft
is not straight. The shaft is considered straight when no point varies more than 0.003 inch from a
straight line joining the top and bottom reading points. Nothing is normally done to correct
dogleg or offset unless it is large enough to significantly affect the static runout. If necessary,
dogleg can be corrected by shimming the coupling. Offset is rarely large enough to cause a
problem and usually can be corrected only by remachining the coupling flanges and reboring the
coupling bolt holes.
4. EQUIPMENT
The basic equipment required for vertical shaft alignment consists of:
·
At least four dial indicators with bases.
·
Feeler gauges for measuring bearing, seal ring, and other clearances.
·
A taper gauge or other means of measuring the generator air gap.
·
Inside micrometers for measuring the distance between the shaft and bearing brackets.
·
Some means of measuring plumb.
Plumb readings can be taken using the traditional plumb wire system or a laser-based system.