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Shaft Alignment by the Numbers

Foundations, soft foot, pipe strain, indicators and sag, rim and face, reverse indicator, thermal growth, shims and couplings, on one pump set

How to align coupled machines and prove it: misalignment, foundations, levelling, soft foot, pipe strain, dial indicators, rim and face, reverse indicator, thermal growth, shims and couplings.

10 chapters · About 100 minutes · Free to read · Intermediate maintenance and installation engineering

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KEVOS® LibraryENGINEERINGShaft Alignmentby the NumbersKEVOS® ORIGINAL BOOK10 CHAPTERS

About this book

Two shafts joined by a coupling should run as one: their centrelines continuing each other in a straight line while the machines are at their working temperature. They rarely start that way. Foundations settle, baseplates twist when they are bolted down, pipes pull on pump casings, machines grow as they warm, and indicators mounted on brackets sag under their own weight. Each of those effects is small, often a few hundredths of a millimetre, and each is enough to shorten the life of bearings, seals and couplings.

This book shows how to get two shafts into line and prove they are there. It starts with what misalignment is and how it is measured, then prepares the machine: foundation, baseplate, levelling, soft foot and pipe strain. It covers dial indicators and their sag, the rim and face and reverse indicator methods, thermal growth, the moves that correct the alignment, and the coupling and records that close the job.

It is for maintenance fitters, millwrights, reliability engineers and installation supervisors. It assumes trade or engineering training and familiarity with dial indicators and hand tools; it explains the geometry as it is used. Each chapter works the running case with real numbers, includes one plausible mistake and how it was found, links the KEVOS® tools that do the chapter’s calculations, and ends with an exercise and its worked answer.

The running case

Every chapter follows one installation. This is an illustration. A food manufacturer in Dandenong South, Victoria, is installing the HW-3 hot water pump set, which circulates water at 85 °C round a pasteuriser loop, in a new pump room.

  • Driver: a 55 kW, four-pole electric motor running at 1,480 rpm, with a 65 mm shaft whose centreline is 250 mm above its feet. Its front feet are 320 mm and its back feet 669 mm from the plane where alignment readings are taken on its coupling hub.
  • Driven machine: an end-suction centrifugal pump whose shaft centreline is 280 mm above its feet. The pump is the stationary machine; the motor is moved to align to it.
  • Coupling and base: a flexible coupling, a fabricated steel baseplate and a concrete block, with a total machine and baseplate mass of 1,450 kg.
  • Site tolerances: at most 0.05 mm offset and 0.05 mm per 100 mm angularity at the coupling when running, 0.05 mm of soft foot at any foot, and 0.05 mm of movement at the coupling from pipe strain.

Dimensions, readings, temperatures, ratings, tolerances, masses and times are the case site’s working figures or are calculated from stated assumptions. They do not describe KEVOS® work or any real business, plant or supplier’s data.

How to use the book

Read Chapter 1 first. Chapters 2 to 4 prepare the machine and can be read in order before any alignment. Chapter 5 covers the measuring tools on which every later chapter depends. Chapters 6 and 7 present the two main dial indicator methods, and either can be used alone. Chapter 8 adds thermal growth, Chapter 9 the moves and Chapter 10 the coupling, acceptance and records.

Every calculation in the book was checked by running it, and the KEVOS® tools linked from each chapter were checked against the calculations they perform. Laser alignment systems do the same geometry electronically; the book uses dial indicators because their numbers show the geometry, and because a laser system’s results are best understood, and checked, in the same terms.

Source limits and professional responsibility

This book is educational. Its methods are standard alignment practice, but tolerances for a real machine come from its coupling and machine makers or from an alignment standard adopted by the site, and foundations must be designed by a structural engineer. Alignment is done on stationary machines that must be isolated from all energy sources and locked out before work starts, as required for plant under the model WHS laws. Decisions about real machines remain with the competent people responsible for them.

Who this book is for

Maintenance fitters, millwrights, reliability and maintenance engineers, and installation supervisors who install, align, check and sign off motors, pumps, fans, gearboxes and other coupled machines.

What you will learn

  • Describe misalignment as offset and angularity in two planes, convert between the units in use, and explain what it does to couplings, bearings and seals.
  • Prepare a machine for alignment: foundation, baseplate, levelling, soft foot and pipe strain, each with a measured acceptance.
  • Take valid dial indicator readings, measure and correct bracket sag, and use the validity rule to reject a bad set.
  • Calculate foot corrections by the rim and face and reverse indicator methods, and allow for thermal growth between cold and running conditions.
  • Plan and make the shim and horizontal moves, check the coupling's misalignment allowance, and record the final alignment as evidence.

Inside this book

Chapters

  1. 01What misalignment is and what it costsHow to describe shaft misalignment as offset and angularity in two planes, convert between the units in use, and understand what misalignment does to couplings, bearings and seals.
  2. 02Foundations, baseplates and groutWhy alignment starts with the foundation: a first estimate of a concrete block for mass, bearing pressure and resonance, and how baseplates, grout and holding-down bolts hold alignment.
  3. 03Levelling and soft footHow levelling wedges set a base and whether they hold, what soft foot is, how to measure it at every foot, how to tell parallel, angled and induced soft foot apart, and how to shim.
  4. 04Pipe strainHow connected pipes pull a pump out of alignment, how to support pipe weight and absorb thermal growth so the pump carries neither, and how to measure pipe strain at the coupling.
  5. 05Dial indicators, brackets and sagHow dial indicator readings round a coupling relate to offset, how to measure and correct bracket sag, and how the validity rule catches a bad set of readings before it is used.
  6. 06The rim and face methodHow rim and face dial readings give offset and angularity at the coupling, how similar triangles turn them into corrections at the feet, and how to check the signs before moving.
  7. 07The reverse indicator methodHow two rim readings, one from each shaft, locate the movable shaft at two planes, how to turn them into foot corrections by calculation or plotting, and why the method suits spacers.
  8. 08Thermal growth and cold targetsHow machines grow as they warm, how to estimate each machine's vertical growth from its centreline height and support temperature, and how to set a cold target that is true hot.
  9. 09Making the movesHow to combine readings and thermal growth into cold shim corrections, choose shims, make the vertical then horizontal moves against indicators, and confirm the running result.
  10. 10Couplings, acceptance and recordsHow to check a flexible coupling's torque, speed, misalignment and key ratings, why its allowance is not an alignment tolerance, and how to accept, record and re-check alignment.

Apply This in Practice

Use these KEVOS® tools to try the method from this reading with your own numbers.

References and source notes

The manuscript and worked examples are original KEVOS® writing. References inform particular concepts; their authors do not endorse this book. Web references were consulted on 1 November 2026.

  • H. Kleinert, World Scientific, Singapore. Gauge Fields in Condensed Matter, Volume II: Stresses and Defects (Differential Geometry, Crystal Melting) (1989). In copyright. Part IV was used only as a map of ideas: parallelism and the transport of a direction from one place to another, and the closure of a circuit as a test for a defect, which this book applies to readings round a coupling. No text, equations, figures or problems are reproduced, and all cases and calculations are KEVOS® originals.
  • J. Piotrowski, CRC Press. Shaft Alignment Handbook, third edition (2006). Background for the effects of misalignment, soft foot and pipe strain, bracket sag, the rim and face and reverse indicator methods, thermal growth and the moves in Chapters 1 and 3 to 9.
  • Acoustical Society of America. ANSI/ASA S2.75-2017/Part 1 Shaft Alignment Methodology, Part 1: General Principles, Methods, Practices, and Tolerances (2017). Named by number and scope only in Chapters 1 and 10. Alignment tolerances for real machines come from such a standard, the coupling maker or the machine maker; the tolerances in this book are the case site's working figures and are labelled as illustrations.
  • American Petroleum Institute. API Recommended Practice 686, Machinery Installation and Installation Design (2009). Named by number and scope only in Chapters 2 to 4, as an industry practice for foundations, grouting, soft foot and piping connections to machinery. No values are quoted from it.
  • International Organization for Standardization. ISO 20816-1 Mechanical vibration — Measurement and evaluation of machine vibration — Part 1: General guidelines (2016). Named by number and scope only in Chapter 10, as the general framework for evaluating machine vibration after alignment.
  • Safe Work Australia. Model Code of Practice: Managing the risks of plant in the workplace (2022). Named in Chapters 1, 4 and 9 for the duty to isolate plant from energy sources before work such as alignment, and to manage the risks of rotating machinery under the model WHS laws.

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