MILITARY SEALIFT COMMAND

Shaft Alignment

2UNCLASSIFIED OPR: N7

• Define “Soft Foot” condition• Define “Bar Sag” and discuss how to correct

using dial indicators• Define “Thermal Growth” as it relates to shaft

alignment

Alignment Objectives

3UNCLASSIFIED OPR: N7

• Shaft alignment is…– positioning shafts so they rotate about the same centerline.

• Shaft mis-alignment occurs when...– ...end-coupled shafts do not rotate about the same centerline.

Shaft Alignment Goals

4UNCLASSIFIED OPR: N7

Misalignment Results In …

VIBRATIONReduced Operating Life

OPERATING HOURS

OPERATING COST

And

5UNCLASSIFIED OPR: N7

• Specification Errors

• Mechanical Errors

• Improper Methods

Causes of Misalignment

6UNCLASSIFIED OPR: N74

HOT

COLD

Thermal Growth Improper Installation

Lack of TrainingLack of Training

Specification Errors

7UNCLASSIFIED OPR: N7

FoundationFlexure

Shock

Corrosion

BentShaft

Loose Bolts / Soft Foot

Mechanical Problems

8UNCLASSIFIED OPR: N7

Wrong Tools:

• Ruler

• Level

• Carpenters Square

• Feeler Gage

Coupling Alignment

Coupling faces can be perfectly aligned while shafts are misaligned

Improper Techniques

9UNCLASSIFIED OPR: N7

Proper Techniques

• Reverse Indicator Method• Using Dial Indicators• Using Lasers

• Rim and Face Method• Using Dial Indictors

10UNCLASSIFIED OPR: N7

Reverse Indicator Method

"A" DISTANCE BETWEEN INDICATORS"B" DISTANCE FROM COUPLING CENTER TO "MI""C" DISTANCE FROM "MI" TO FRONT FOOT"D" DISTANCE BETWEEN MOTOR SUPPORTS"MI" "MOTOR" INDICATOR (DRIVER)“PI" "PUMP" INDICATOR (DRIVEN)"MTBM" "MACHINE TO BE MOVED"

StationaryMachine

MTBM

CL

B

A

C D

MI

PI

11UNCLASSIFIED OPR: N7

Rim and Face Method

IndicatorRim

FaceIndicator

12UNCLASSIFIED OPR: N7

Dial Indicators or Lasers?

Sag

Sag

L R

no sag LR

Dial Indicators• Must ensure bar sag is taken

into consideration.

• This adds complexity to themathematics.

• Kit cost is approx $2000

Lasers• Bar sag is not an issue

• This simplifies the mathematics.

• Kit cost ranges from $3.6K to$20K

13UNCLASSIFIED OPR: N7

Types of Misalignment

Offset

Centerlinesmeet at

coupling center

Angularity

Parallel

AngularAngularity

Centerlines meet at coupling center

14UNCLASSIFIED OPR: N7

Types of Misalignment

Skewed Misalignment (most common type)

Angular + Parallel

Centerlinesdo not meet

at coupling centerCenterlines do

not meet at coupling center

15UNCLASSIFIED OPR: N7

Dowel Pins

TAPER=1/4" / FOOT

MATERIAL: 304 STAINLESS

Typical Dowel Pin

Machine Foot

Base Plate

Pin Removal

WashersNut

Installation

Base Plate

Machine Foot

Hold Down Bolt

Dowel Pin• Repositions machine after repair• Prevents horizontal drift

16UNCLASSIFIED OPR: N7

• Misalignment will significantly shorten the lifeof a machine

• Shaft alignment is always preferable tocoupling alignment

• Ensure contractors and shipyard workers areproviding a precision alignment

• For more information see the alignmenttextbook on the CMEO CD ROM

Summary