Alignment, Levelling and Balancing
Overview
Alignment, Levelling and Balancing is a critical chapter in ITI Fitter Semester 3 (NCVT). It covers methods to ensure machine components are correctly positioned, horizontal surfaces are true, and rotating parts are balanced. Proper alignment prevents vibration, bearing failure, and premature wear. Levelling ensures machines sit flat on foundations. Balancing eliminates centrifugal forces in rotating parts. These skills are essential for installation, maintenance, and precision fitting work in industrial settings.
Typed Notes
Alignment — Principles and Methods
Alignment means bringing two or more machine parts (shafts, couplings, bearings) into their correct relative positions. Misalignment causes vibration, noise, excessive bearing load, and seal failure. Two main types: (1) Angular misalignment — shaft centre lines meet at an angle; corrected by shimming one machine foot. (2) Parallel (offset) misalignment — shaft axes are parallel but displaced; corrected by moving the machine laterally or vertically. Methods of checking: straight edge, dial indicator (DTI), reverse-indicator method, and laser alignment. Reverse-indicator method is most accurate for flexible couplings. Permissible misalignment for flexible couplings is typically within 0.05 mm TIR.
Levelling — Tools and Procedure
Levelling ensures a machine base or surface is perfectly horizontal (or at a specified inclination). Tools used: Spirit level (bubble level), precision engineer's level, autocollimator, and water level. Spirit level sensitivity: 0.02 mm/m means the bubble moves one division when one end is raised 0.02 mm over 1 metre. Procedure: Place level longitudinally and transversely; adjust foundation bolts or shims until bubble is centred. Wedge-type and jack-bolt type shims are common. Machine beds are levelled before grouting. Autocollimator measures angular errors up to 0.5 seconds of arc and is used for precision machine tool alignment. Straight edge and surface plate are used for local flatness checks.
Balancing — Static and Dynamic
Balancing removes unequal mass distribution in rotating parts to eliminate centrifugal forces. Static balancing: A part is statically balanced when its centre of gravity lies exactly on the rotation axis. Test: mount part on knife-edge rails; it should not rotate to any preferred position. Used for narrow disc-type parts (grinding wheels, pulleys). Dynamic balancing: Required for long rotating parts (crankshafts, turbine rotors, fan impellers). Even if statically balanced, a long rotor can have a couple imbalance causing vibration at speed. Dynamic balancing is done on a balancing machine; correction masses are added or removed at two planes. Units of imbalance: g·mm or g·cm.
Instruments and Checks in Practice
Dial Test Indicator (DTI): Measures shaft run-out and coupling alignment; least count 0.01 mm, range typically 0–10 mm. Total Indicator Reading (TIR) = maximum reading − minimum reading. Feeler gauge: Checks coupling gap and parallelism; available in sets of 0.05–1.0 mm blades. Straight edge: Steel straight edge placed across a surface to detect high/low spots using feeler gauge. Piano wire and plumb bob: Used for long-distance alignment of large machinery (turbines, paper machines). Laser alignment system: Projects laser beam; receiver shows offset and angle directly in digital readout — fastest and most accurate modern method. Always check alignment after final grouting and thermal expansion at operating temperature.
Topics & Sub-topics
Har topic ke saath sub-topics aur example — chapter ka complete coverage.
01Shaft Alignment
- Types: Angular and Parallel (Offset) misalignment
- Checking methods: Straight edge, DTI, Reverse-indicator, Laser
- Correction methods: Shimming, lateral movement of machine
- Permissible limits and TIR calculation
A pump coupled to a motor shows 0.12 mm TIR on DTI; technician adds 0.06 mm shim under motor rear feet to correct angular misalignment, bringing TIR within 0.05 mm limit.
02Levelling of Machines
- Spirit level — sensitivity 0.02 mm/m per division
- Autocollimator for precision angular measurement (0.5 arc-second)
- Shimming and grouting procedure
- Longitudinal and transverse levelling checks
A lathe bed 2 m long is levelled: spirit level placed at headstock end reads 2 divisions off; technician inserts 0.04 mm shim (2 × 0.02 mm/m × 1 m) under that foot to centre the bubble.
03Static and Dynamic Balancing
- Static balancing — knife-edge rail test for disc-type parts
- Dynamic balancing — two-plane correction for long rotors
- Balancing machine operation and correction mass addition/removal
- Units of imbalance: g·mm; ISO balance quality grades (G-grades)
A 300 mm diameter grinding wheel is tested on knife-edge rails; it rotates to a heavy spot at bottom — a 5 g piece of material is ground off the heavy side until the wheel stays stationary in any position.
04Alignment and Levelling Tools
- Dial Test Indicator (DTI) — LC 0.01 mm, range 0–10 mm
- Feeler gauge set — blade range 0.05 mm to 1.0 mm
- Straight edge and surface plate for flatness
- Piano wire, plumb bob, and laser alignment system
During turbine installation spanning 8 m, engineers stretch a 0.5 mm diameter piano wire between two end supports and use a micrometer-reading wire gauge at each bearing pedestal to check alignment within 0.1 mm.
05Coupling Alignment Procedure
- Rim and face method using two DTIs
- Reverse-indicator method for flexible couplings
- Soft-foot check before alignment (all four feet must contact base)
- Thermal growth allowance at operating temperature
In reverse-indicator alignment of a centrifugal pump, DTI on motor hub reads +0.10 mm at top and −0.10 mm at bottom (TIR = 0.20 mm offset); motor is shifted 0.10 mm upward to achieve zero offset.
Key Concepts
Revision ke liye ek nazar — exam se pehle yahi padhna hai.
- 01Spirit level sensitivity is expressed in mm per metre or seconds of arc; a standard precision level reads 0.02 mm/m per division.
- 02Shaft alignment errors are of two types: Angular misalignment (shafts at an angle) and Parallel/Offset misalignment (shafts parallel but offset).
- 03Static balancing requires the centre of gravity to lie on the axis of rotation; dynamic balancing additionally requires the principal axis to coincide with the rotation axis.
- 04Dial Test Indicator (DTI) is used for checking shaft alignment; least count is typically 0.01 mm.
- 05Feeler gauges, straight edges, piano wire, and optical instruments (autocollimator) are key levelling and alignment tools.
Questions & Solutions
Pehle khud try karo — phir solution kholo. Yahi tariqa topper banata hai.
What are the two main types of shaft misalignment and how is each corrected?
Define sensitivity of a spirit level and give a standard value used in machine levelling.
Distinguish between static balancing and dynamic balancing with one example each.
What is TIR and what is the permissible TIR for flexible coupling alignment?
List any four tools used for alignment and levelling in a fitting shop and state one use of each.
Alignment corrects angular and parallel shaft errors using DTI and laser tools. Levelling uses spirit levels (sensitivity 0.02 mm/m) and autocollimators to set machine bases true. Static balancing places CG on rotation axis (knife-edge test); dynamic balancing corrects couple imbalance in two planes using a balancing machine. Correct alignment and balancing prevent vibration, bearing failure, and energy loss — core competencies for an ITI Fitter.
Chapter-end quiz
4 MCQsOption tap karo — turant pata chalega sahi ya galat, explanation ke saath.
Q1.The sensitivity of a standard precision engineer's spirit level is:
Q2.Which method of shaft alignment is considered most accurate for flexible couplings?
Q3.A grinding wheel is balanced on knife-edge rails and always rotates to one position. This indicates:
Q4.The least count of a standard Dial Test Indicator (DTI) used for alignment checks is:
Mark karo — dashboard par progress dikhega.