AtlasCalcsUtility Calculation Suite
2026-07-30 8 min

Gear Inspection Calculator

Calculate gear inspection results and health score based on dimensional measurements, surface condition, and operating parameters.

Calculator

Gear Type
Number of Teeth
Module (mm)
Face Width (mm)
Gear Quality Grade (ISO 3-12)
Tooth Thickness Deviation (mm)
Tooth Pitch Error (μm)
Runout (μm)
Surface Finish Ra (μm)
Contact Pattern Coverage (%)
Backlash (mm)
Operating Hours
Pitting Area (%)
Wear Depth (mm)
Vibration Level (mm/s)
Noise Level (dBA)

Results

Optimal

Overall Gear Health Score

91%

Composite gear health score based on all inspection parameters

Tooth Condition

98%

Assessment of tooth thickness, pitting, and wear

Pitch/Runout Assessment

83%

Combined pitch error and runout measurement score

Surface Condition

89%

Surface finish and contact pattern quality

Contact Pattern

85%

Percentage of tooth surface showing proper contact

Quality Grade Assessment

ISO 6

Effective ISO gear quality grade based on measurements

Inspection Status

Pass

Overall pass/fail/conditional inspection result

Recommended Action

No Action

Recommended maintenance action based on inspection results

Remaining Life Estimate

45500hours

Estimated remaining operating life

Visualizations

Results Overview

91%Overall Gear Health Score
98%Tooth Condition
83%Pitch/Runout Assessment
89%Surface Condition
85%Contact Pattern
6%Quality Grade Assessment
45,500%Remaining Life Estimate

Formula

Weighted average inspection scoring system for gear condition assessment.

Gear_score = Σ(w_i × score_i) / Σw_i

Alternative Form

Health_Score = ≥80% Pass, 60-79% Conditional, <60% Fail

Variables

SymbolNameUnitDescription
w_iWeight Factor-Relative importance weight for each inspection parameter
score_iParameter Score%Individual score for each inspection parameter (0-100%)
ΣSummation-Sum of all weighted parameter scores

Explanation

The gear inspection score is a weighted composite of individual parameter scores. Each measurement is converted to a percentage score based on deviation from the ideal or allowable tolerance, then combined using predefined weights reflecting the relative importance of each parameter to overall gear health.

Derivation

The scoring system is derived from ISO 1328 gear inspection standards and AGMA gear rating practices. Parameter tolerances are based on ISO quality grades. The weighting system reflects failure mode criticality: tooth condition (wear, pitting) is most critical, followed by geometric accuracy (pitch, runout), then surface and operating condition indicators.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Enter gear specifications — type, teeth, module, and face width.

Gear Type:Spur
Teeth:40
Module:5 mm
Face Width:50 mm
Result: Pitch Diameter = 200 mm
Step 2

Enter dimensional measurements — tooth thickness deviation, pitch error, runout, and surface finish.

Thickness Dev:0 mm
Pitch Error:10 μm
Runout:20 μm
Ra:0.8 μm
Result: Tooth Score = 100%
Step 3

Enter surface condition and operating indicators — contact pattern, pitting, wear, vibration, and noise.

Overall = Σ(w × score) / Σw
Contact:85%
Pitting:2%
Vibration:2.5 mm/s
Intermediate: Overall = Σ weighted scores / total weight
Result: Gear Health Score = 91% → Pass
Final Answer
91

Worked Examples

See how the calculator works with different scenarios.

Scenario

A newly manufactured spur gear with 40 teeth, module 5, ISO grade 7 specification. Measurements: tooth thickness +0.02 mm, pitch error 6 μm, runout 12 μm, surface finish Ra 0.4 μm, contact pattern 90%.

Inputs

Teeth:40
Module:5
Grade:ISO 7
Pitch Error:6 μm
Runout:12 μm
Ra:0.4 μm
Contact:90%

Calculation

Tooth thickness score: 100 - (0.02/0.10 × 20) = 96% Pitch score: 100 - (6/10 × 25) = 85% Runout score: 100 - (12/50 × 25) = 94% Overall weighted score ≈ 91%

Result

91% — Pass (meets ISO grade 7)

Interpretation

The gear is in excellent condition and meets ISO grade 7 specifications. Minor tooth thickness deviation is within acceptable tolerance. No action required.

Understanding Your Result

Your Result: Overall Gear Health Score: 91 %

Typical range: New gears: 85-100% (Pass). Serviceable: 65-84% (Conditional). Worn: 50-64% (Plan Repair). Critical: <50% (Replace). ISO grades 3-12 with 3 being most precise.

What This Means

The gear inspection score is a comprehensive health indicator that combines dimensional accuracy, surface condition, and operating parameters into a single actionable assessment.

Why It Matters

Gear failures can cause catastrophic damage to drivetrains and create safety hazards. Regular inspection and condition assessment allows planned maintenance rather than emergency replacement.

Professional Interpretation

The weighted scoring system emphasizes tooth condition (thickness, pitting, wear) and geometric accuracy (pitch, runout) as the primary determinants of gear health. Surface condition and contact pattern provide leading indicators of developing problems. Vibration and noise are lagging indicators that often indicate established damage. Always cross-reference inspection scores with oil analysis (wear particle count) and ferrography for a complete assessment.

Recommendations

  • •Perform gear inspections at regular intervals based on criticality and operating hours
  • •Use oil analysis and ferrography as complementary condition monitoring tools
  • •Document inspection results to establish degradation trends over time
  • •Consider gearbox alignment and foundation condition when interpreting results
  • •Replace gears in matched sets to ensure proper tooth contact and load sharing

Educational Content

Introduction

Gear inspection is a critical maintenance activity that assesses the condition and remaining life of gear drives. Dimensional measurements, surface analysis, and operating condition monitoring combine to provide a comprehensive health assessment.

Concept Explanation

Gears degrade through multiple mechanisms: abrasive wear from contaminated lubricant, adhesive wear (scuffing) from inadequate lubrication, pitting fatigue from surface contact stress, bending fatigue at tooth roots, and plastic deformation from overload. Each failure mode produces characteristic changes that can be detected through dimensional measurement, surface examination, and operating parameter monitoring.

Applications

▸Industrial gearbox condition assessment
▸Wind turbine gearbox inspection programs
▸Automotive transmission quality control
▸Aerospace gear health monitoring
▸Mining and heavy equipment gear maintenance
▸Machine tool spindle gear inspection
▸Marine propulsion gear system assessment

Benefits

  • •Prevents catastrophic gear failure and secondary damage
  • •Extends gear life through early problem detection
  • •Optimizes maintenance scheduling and reduces downtime
  • •Supports root cause analysis of gear failures
  • •Provides objective data for repair vs. replace decisions

Limitations

  • •Requires specialized measurement equipment and skilled technicians
  • •Some measurements require gearbox disassembly
  • •Surface inspection limited to accessible tooth areas
  • •Scoring system is heuristic and may not capture all interactions

Best Practices

  • •Establish baseline measurements for new or rebuilt gears
  • •Use consistent measurement positions and techniques
  • •Combine dimensional inspection with oil analysis and vibration monitoring
  • •Train inspectors in proper gear measurement methods
  • •Maintain detailed inspection records with photographs

Common Misconceptions

Myth: A gear that passes inspection is in perfect condition.
Truth: Inspection detects measurable deviations but cannot identify all potential failure modes, especially subsurface defects or material quality issues.
Myth: Higher ISO grade always means better gear performance.
Truth: Higher precision (lower grade number) is not always necessary. The appropriate grade depends on speed, load, and application. Over-specifying grade adds cost without benefit.
Myth: Contact pattern is the most important inspection parameter.
Truth: Contact pattern is important but tooth geometry (pitch, runout, thickness) and material condition (pitting, wear) are equally critical. All parameters must be considered together.

Practical Tips

  • •Clean gear teeth thoroughly before inspection to ensure accurate measurements
  • •Use gear tooth vernier calipers or gear tooth micrometers for tooth thickness measurements
  • •Measure pitch error over several tooth pairs to get statistically significant data
  • •Use parallel bars or feeler gauges to check alignment of gear shafts
  • •Document contact patterns with photographs for comparison over time
  • •Verify measurement equipment calibration before each inspection
  • •Check multiple teeth across the gear circumference, not just the best-looking ones

Common Mistakes

Measuring tooth thickness at the wrong position on the tooth flank
Tooth thickness should be measured at the pitch circle, perpendicular to the tooth profile. Use the addendum reference from the gear specification to locate the correct measurement position.
Confusing pitch error with cumulative pitch error
Adjacent pitch error measures the difference between consecutive tooth spacings. Cumulative pitch error measures the total error over a complete revolution. Both are important for different failure modes.
Ignoring the effects of temperature on gear measurements
Gear dimensions change with temperature. Allow the gear to stabilize at room temperature (20°C) before measuring. Apply correction factors if measurement at operating temperature is necessary.
Inspecting gears without reference to original specifications
Always use the original gear design specifications (tooth thickness, module, pressure angle) as the reference. Measuring against incorrect specifications gives misleading results.

Assumptions

This calculator makes the following assumptions to provide estimates:

Linear Scoring: Assumes linear relationship between measurement deviation and score. In reality, the criticality of deviation increases non-linearly approaching tolerance limits.
Independent Parameters: Assumes inspection parameters are independent. In reality, pitch error and runout are related, and combined effects may be more severe than individual scores suggest.
Equal Tooth Loading: Assumes all teeth share load equally. Manufacturing variations, alignment errors, and torsion deflection cause uneven load distribution.
Steady Operating Conditions: Assumes consistent operating conditions. Variable loads, speeds, and temperatures may cause intermittent overloading not captured by static measurements.

Limitations

Be aware of these limitations when using this calculator:

Measurement Accuracy: Results depend heavily on measurement accuracy and technique. Operator skill, equipment calibration, and environmental conditions all affect measurement quality.
Surface Inspection Access: Full tooth surface inspection may require gear disassembly. In-situ inspection is limited to accessible areas and may miss localized damage.
No Material Testing: The inspection does not include material hardness testing, metallurgical analysis, or subsurface defect detection (cracks, inclusions).
Empirical Scoring: The weighted scoring system is heuristic. Actual criticality of each parameter depends on gear type, application, and operating conditions.

Frequently Asked Questions

Answers to common questions about this calculator.

What is a gear health score?
The gear health score is a composite percentage (0-100%) combining dimensional accuracy, surface condition, and operating condition indicators. It provides an overall assessment of gear condition for maintenance decision-making.
What is the ISO gear quality grade?
ISO 1328 defines quality grades from 3 (most precise) to 12 (least precise). Grade 6-7 is typical for general industrial gearing. Grade 3-5 for precision applications (aerospace, high-speed). Grade 8-12 for low-speed or non-critical applications.
How do I interpret inspection results?
Score ≥80%: Gear is in good condition. Score 60-79%: Degradation detected, monitor closely. Score 40-59%: Significant wear, plan repair. Score <40%: Critical condition, replace urgently.
What is the most important gear inspection measurement?
Tooth thickness and pitch error are typically most important as they directly indicate wear and geometric degradation. However, for surface-initiated failures (pitting, scuffing), surface condition is more critical.
How often should gears be inspected?
For critical gears: annually or every 5000 operating hours, whichever comes first. For non-critical: every 2-3 years. Increase frequency if vibration, noise, or oil analysis indicate developing problems.
What is pitting in gears and when is it critical?
Pitting is surface fatigue where small pieces of material break away from the tooth surface. At <5% of tooth area: monitor. At 5-15%: plan repair. At >15%: replace urgently as pitting accelerates rapidly once initiated.
How does backlash affect gear operation?
Backlash provides clearance for lubrication and accommodates thermal expansion. Too little backlash causes binding and overheating. Too much backlash causes noise, vibration, and impact loading. Typical backlash for industrial gears: 0.1-0.5 mm.
What is an acceptable contact pattern?
A proper contact pattern should cover 80-95% of the tooth face width and be centered on the tooth flank. Off-center or edge contact indicates misalignment. Low coverage indicates geometric errors in the gear profile.
How do I measure tooth thickness?
Use a gear tooth vernier caliper to measure the chordal tooth thickness at the pitch circle. Alternatively, measure over pins (ball method) for higher accuracy. Compare against the nominal thickness from the gear drawing.
What causes high pitch error?
High pitch error can result from manufacturing inaccuracies, gear wear (especially uneven wear), bearing wear causing eccentricity, or shaft deflection. Pitch error increases vibration and noise.
What is gear runout and how is it measured?
Runout is the radial variation of the gear when rotated. Measure with a dial indicator contacting the pitch circle or a reference diameter. High runout causes periodic vibration at the rotational frequency.
How does surface finish affect gear performance?
Surface finish affects friction, wear rate, and lubrication film formation. Smoother surfaces (Ra <0.4 μm) are needed for high-speed gears. Rougher surfaces (Ra >1.6 μm) are acceptable for slow-speed gears but increase wear rate.
What is scuffing in gears?
Scuffing is adhesive wear caused by breakdown of the lubricant film, resulting in metal-to-metal contact and material transfer between mating tooth surfaces. It appears as rough, torn areas on the tooth flank.
How does vibration measurement help in gear inspection?
Vibration analysis can detect gear mesh frequency components, sidebands indicating modulation, and harmonic patterns characteristic of specific faults like tooth breakage, pitting, or misalignment.
What are the limits for vibration in gearboxes?
Per ISO 10816: Good: <3 mm/s, Acceptable: 3-7 mm/s, Unsatisfactory: 7-15 mm/s, Unacceptable: >15 mm/s. These limits depend on gearbox size, mounting, and criticality.
What noise levels indicate gear problems?
Baseline noise depends on gear type, speed, and enclosure. A sudden increase of 5-10 dBA above baseline, or tonal noise at gear mesh frequency, indicates developing problems. Noise >90 dBA generally requires investigation.
How does lubrication affect gear inspection results?
Poor lubrication accelerates wear, increases friction, and raises operating temperature. Oil analysis (viscosity, additives, particle count) provides complementary condition data. Inspect lubricant condition at each gear inspection.
What is the relationship between gear wear and operating hours?
Wear is not linear with hours. Initial break-in wear (first 500 hours) establishes the contact pattern. Steady-state wear proceeds slowly. Wear accelerates exponentially as clearances increase and surface fatigue initiates.
How do I assess gear alignment?
Use feeler gauges to check shaft parallelism, measure bearing housing positions, and observe contact pattern distribution. Off-center contact indicates alignment issues. Shaft alignment should be within 0.05 mm/m for gear drives.
What is the effect of operating temperature on gear inspection?
Temperature effects include: thermal expansion changing backlash and clearance, accelerated wear at high temperature, lubricant degradation, and potential material property changes above 150°C.
Can gears be repaired or must they be replaced?
Minor pitting and wear can be addressed by improving lubrication and operating conditions. Significant geometry changes, deep pitting (>0.5mm), or tooth cracking require replacement. Some large gears can be remanufactured by grinding.
How do I select gear inspection intervals?
Base intervals on: gearbox criticality, operating hours, previous inspection results, oil analysis trends, and manufacturer recommendations. Adjust based on observed degradation rate.
What is the difference between tooth contact analysis (TCA) and standard inspection?
TCA analyzes tooth contact under simulated operating conditions, detecting contact pattern, transmission error, and load distribution. Standard inspection measures static geometric parameters. TCA provides more detailed dynamic assessment.
How does gear material affect inspection criteria?
Different materials have different failure modes. Case-hardened gears are prone to pitting and spalling. Through-hardened gears show uniform wear. Nitrided gears resist scuffing but are brittle. Stainless gears resist corrosion but wear faster.
What inspection equipment is needed for gear inspection?
Basic: gear tooth calipers, micrometers, dial indicators, surface roughness tester. Advanced: gear measuring machine (CMM with rotary table), profile and lead measurement systems, coordinate measuring machines with gear analysis software.
How do I document gear inspection results?
Record: date, gear identification, operating hours, all measurement values, contact pattern photos, and action taken. Maintain a trend chart for each parameter to visualize degradation over time.
What is the role of ferrography in gear condition monitoring?
Ferrography analyzes wear particles in the lubricant. Normal wear produces small platelets. Abnormal wear produces larger particles with distinctive morphologies: spheres (fatigue), chunks (spalling), ribbons (cutting wear).
How does gear speed affect inspection parameter tolerances?
Higher speeds require tighter tolerances for pitch, runout, and balance. At high speeds, small geometric errors produce significant vibration. ISO grade requirements should be matched to operating speed.
What is the acceptable tooth thickness reduction before replacement?
Generally, 10% reduction in tooth thickness from wear indicates replacement should be planned. 15-20% reduction requires immediate replacement. These limits depend on load, speed, and safety factor.

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Glossary

Technical terms used in mortgage calculations explained in plain language.

Pitch Circle
The imaginary circle on which tooth spacing and profile are based, representing the effective diameter for power transmission between mating gears.
Module
The ratio of pitch circle diameter to number of teeth (mm). The fundamental metric gear sizing parameter.
Backlash
The circumferential clearance between mating gear teeth, measured at the pitch circle, necessary for lubrication and thermal expansion.
Runout
Radial eccentricity of the gear when mounted on its axis, measured as total indicator reading (TIR).
Pitting
Surface fatigue damage characterized by small craters on tooth flanks, caused by repeated contact stress exceeding the material fatigue limit.
Contact Pattern
The area of tooth surface showing evidence of contact with the mating gear, evaluated as a percentage of tooth face width.
Scuffing
Adhesive wear caused by lubricant film breakdown, resulting in material transfer and surface roughening.
ISO 1328
International standard defining gear tooth accuracy grades from 3 (finest) to 12 (coarsest).
Transmission Error
The difference between the theoretical and actual angular position of the driven gear, causing vibration and noise.
Ferrography
Analytical technique for sizing, counting, and classifying wear particles in lubricating oil to assess machine condition.

Authoritative References

Trusted sources and standards referenced by this calculator.

Applicable Standards

ISO 1328-1ISO 10816AGMA 2000AGMA 2116DIN 3962DIN 3990

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Page Information

Last Updated:

2026-07-30

Version:

2.0.0

License:

Free to use for educational and professional purposes.