MILLWRIGHTQC

Shaft Alignment

Check the sign convention once, on a machine you can measure with a rule. This page assumes a standard indicator reading positive when the plunger is depressed, zeroed at 12 o’clock. A reversed lever indicator, a mirrored bracket, or a shop that zeroes at the bottom inverts every vertical answer below — and the wrong answer looks entirely plausible.

Readings

Zero at 12 o’clock, then read at 3, 6 and 9. Thousandths of an inch, signed.

Plane A — indicator on the stationary machine, reading the movable hub

Plane B — indicator on the movable machine, reading the stationary hub

Both indicators on the stationary machine, reading the movable hub. Zero at 12 o’clock, then read at 3, 6 and 9.

Rim — where the shaft is

Face — what angle it runs at

Sag is taken out of the rim readings only. A measured sag figure is radial droop from a test bar; a drooping bracket also rotates slightly, which moves a face reading, but that is a different quantity and nothing here has measured it.

Type what the instrument printed, at the coupling. In mils and mils per inch, which is how printouts state it and how the record stores it.

Check the sense once. This assumes the movable shaft relative to the stationary one, positive up and toward 3 o’clock, and an angularity that is positive where the movable shaft rises going away from the coupling. Instruments do not all agree, and a printout read the other way round gives an ordinary-looking wrong answer.

Bracket sag

The 6 o’clock reading from a rigid test bar, same bracket, same span. Nearly always negative. Leave blank only if you have measured it and it is zero.

Machine

Inches, measured from plane A, positive away from the coupling.

Cold targets

From the machine’s thermal growth record. Zero for a machine that does not grow — but assumed zero is a real answer and belongs on the record as such.

Tolerance

Result

Enter the readings and the span.