What a Complete Helical Gear Inspection Pack Contains
A complete inspection pack for a precision helical gear from Korea Ever-Power typically contains six documents. Each document verifies a different quality aspect of the helical gear — and each can be checked independently:
1. Gear Analyser Report
Profile deviation, lead deviation, and pitch deviation — determines DIN accuracy class
2. CMM Dimensional Report
Bore, OD, face width, keyway, runout — verifies mechanical fit and assembly compatibility
3. Material Certificate (Mill Cert)
Chemical composition, tensile strength, Charpy impact — confirms material grade and heat batch
4. Hardness Survey
Surface hardness and case depth traverse — confirms heat treatment outcome
5. MPI Report
Magnetic particle inspection — confirms no surface cracks, laps, or grinding burns
6. OES Spectrometer Report
Confirms actual material grade matches mill certificate — catches material substitution
Section 1: The Gear Analyser Report — The Most Important Document
Gear analyser measurement at Korea Ever-Power — each tooth is probed for profile, lead, and pitch deviation. The report shows the measured value versus the DIN tolerance band: any measurement outside the band indicates that specific parameter exceeds the specified DIN class
Profile Deviation Section — ff, Ff, fHα, FHα
The profile section of a helical gear analyser report shows measurements of how closely the actual tooth profile matches the theoretical involute in the transverse plane. Four values are typically reported per tooth:
| Symbol | Name | What It Measures | Why It Matters for Helical Gears |
|---|---|---|---|
| ff (or ffa) | Profile form deviation | Departure of the profile from a perfect involute shape (the “waviness” of the profile) | Directly controls transmission error amplitude — the dominant noise source in helical gears |
| Ff (or Ffa) | Total profile deviation | Maximum spread from highest to lowest point on the profile trace | Includes both form error and slope; used to determine the DIN accuracy class for this parameter |
| fHα | Profile slope deviation | Systematic tilt of the whole profile above or below the perfect involute (pressure angle error) | Shifts the contact zone position — too much can cause edge loading on the tip or root |
| FHα | Total profile slope across all teeth | Worst-case profile slope from all measured teeth | Used in DIN class determination for the profile slope parameter |
Lead Deviation Section — fHβ, Ffβ, FHβ
The lead section measures how closely the actual tooth helix follows the theoretical perfect helix across the face width. This is the parameter that most directly determines face load distribution — the key variable for whether a helical gear operates with even contact across the full face width or with edge loading at one end:
| Symbol | Name | Typical Value (DIN Class 6, M5) | Effect if Exceeded |
|---|---|---|---|
| fHβ | Lead slope deviation | ≤ 8 µm | Systematic tilt of contact zone toward one face edge — edge loading and accelerated pitting at tooth end |
| Ffβ | Lead form deviation | ≤ 9 µm | Wavy lead — multiple contact concentration points across face width, noise at face harmonics |
| Fβ (Fβ = max of fHβ + Ffβ) | Total lead deviation | ≤ 12 µm | Defines the DIN class for the lead parameter — the DIN class shown on the certificate must use this value |
Pitch Deviation Section — fp, fu, Fp
Pitch measurements for a helical gear verify that the angular spacing between successive teeth is uniform around the full circumference. Three values are reported:
- fp (individual pitch deviation): The departure of any single tooth spacing from the average pitch. Controls the once-per-tooth noise excitation at mesh frequency. Typical DIN Class 6 limit for M5: ≤ 7 µm.
- fu (individual pitch difference): The maximum difference between any two adjacent pitch measurements. Controls the gear-to-gear dynamic transmission error during meshing transitions.
- Fp (total cumulative pitch deviation): The maximum spread of cumulative pitch error around the full circumference. Controls the once-per-revolution vibration and affects gear train dynamic balance. Typical DIN Class 6 limit for M5: ≤ 25 µm.
How to Read the DIN Class from the Report
The DIN class stated on a helical gear inspection report is the worst of all individual parameter classes. If the profile deviation gives Class 5, the lead deviation gives Class 6, and the pitch deviation gives Class 7 — the overall DIN class is Class 7. Many reports list individual parameter classes separately — when reading a report for a helical gear, always find the overall (worst-case) DIN class, not the best-performing parameter’s class.
Section 2: Material Certificate — What to Verify
The material certificate (mill certificate, 3.1 certificate per EN 10204) for a helical gear blank must contain three verifiable sections:
| Certificate Section | What to Check | Red Flag |
|---|---|---|
| Chemical composition | C, Mn, Cr, Mo (and Ni for 17CrNiMo6) match the specified grade limits per DIN EN 10083 | Carbon content outside ±0.02% of grade nominal; missing Ni in a certified 17CrNiMo6 spec |
| Mechanical properties | Tensile strength (Rm), yield strength (Rp0.2), elongation (A), and Charpy (KV) at required temperature | Charpy below the specification (e.g. < 27 J at −40°C for Arctic marine gears); elongation below 12% |
| Heat number | The heat (batch) number on the certificate must match the number stamped on the gear blank — providing traceability from finished gear back to the steel mill melt | Certificate without a heat number, or heat number not verifiable on the gear — no traceability |
Section 3: Hardness Survey and Case Depth — What the Numbers Mean
The hardness survey for a carburized or induction hardened helical gear helical gear shows hardness at multiple positions: tooth flank surface, various depths below the surface (the hardness traverse), and the core at the centre of the gear cross-section. What to check:
- Surface hardness: Must meet the drawing specification (e.g. HRC 58–62 for carburized 20CrMnTi). Values below the minimum (e.g. HRC 56) indicate incomplete carburizing or inadequate quench severity.
- Effective case depth: The depth to HV 550 hardness (or as otherwise specified). Must be within the drawing range. Insufficient case depth is a common cause of case crushing under high contact stress.
- Core hardness: Typically HRC 30–40 for carburized gears. Core hardness above HRC 42 indicates excessive through-hardening, which reduces core toughness and shock resistance.
Red Flags — When to Reject or Question a Report
A gear analyser report that shows only average or maximum deviation values, without tooth-by-tooth data around the full circumference, cannot verify DIN class. DIN 3962 requires measurement on all teeth.
“DIN Class 5” stated with no individual parameter measurements. The class statement means nothing without the underlying ff, fHβ, fp, Fp values that it is derived from. Always request the full report.
Profile and pitch measured but no lead deviation reported. For a helical gear, lead deviation is often the critical parameter. A report without lead data is incomplete — particularly for carburized gears where lead distortion is the largest heat treatment effect.
A material certificate without a heat number that matches a marking on the gear provides no actual traceability — the certificate cannot be verified as belonging to the specific gear received. Korea Ever-Power stamps the heat number on every gear blank before machining begins.
Korea Ever-Power — Standard Documentation on Every Order
Korea Ever-Power supplies a complete inspection pack with every helical cut gear helical cut gear order as a standard shipment document — gear analyser report with tooth-by-tooth data, CMM dimensional report, material certificate (EN 10204 3.1) with heat number traceability, hardness survey with case depth traverse, and MPI certificate. As a direct helical gear manufacturer, Korea Ever-Power’s documentation is produced in-house from the same equipment that manufactured the gear — eliminating the documentation gaps that can occur when inspection is subcontracted separately from manufacturing. For customers who receive inspection packs and have questions about specific measurements, Korea Ever-Power’s engineering team provides interpretation support.
Frequently Asked Questions
DIN 3962 requires measurement of all teeth around the full circumference for the pitch deviation parameters (Fp, fu, fp), and at minimum 4–6 equally spaced teeth for profile and lead deviation measurements. A complete gear analyser report for a 24-tooth helical gear therefore contains 24 individual pitch measurements and 4–6 profile/lead traces. Korea Ever-Power measures all teeth for both pitch and profile/lead on every production helical gear, providing 100% gear analyser coverage as standard.
Per EN 10204, a 3.1 certificate is issued by the material manufacturer and validated by their authorised inspector — adequate for most industrial helical gear applications. A 3.2 certificate is additionally validated by an independent third-party inspector (classification society surveyor, nominated by the purchaser) — required for marine, offshore, nuclear, and railway applications where independent verification of the material is mandatory. Korea Ever-Power provides 3.1 certificates as standard and arranges 3.2 certification through Korean Register, DNV, Lloyd’s Register, or Bureau Veritas for applications requiring class society material certification.
The DIN class of a helical gear is determined by the worst-performing individual measurement around the full circumference — not the average, and not the majority. If one tooth out of 24 has a profile deviation that falls in Class 6, and all others are Class 5, the gear is Class 6. This is intentional: a single tooth with excessive deviation creates a once-per-revolution transmission error spike that is perceptible as a “roughness” in the gear noise, regardless of how well the other 23 teeth are made.
Yes — a competitor’s inspection certificate confirms the parameters of the existing gear (assuming it was correctly produced to the certificate). Korea Ever-Power uses the original gear analyser data and material certificate to define the target specification for the replacement gear. If the competitor’s report is incomplete (missing lead deviation, no material traceability), Korea Ever-Power’s reverse engineering service measures the actual gear directly to fill any gaps in the documentation. The replacement helical gear is then produced with Korea Ever-Power’s own full inspection documentation.
Questions About Your Helical Gear Inspection Documents?
Korea Ever-Power’s engineering team reviews received inspection packs and explains any measurement — or supplies replacement gears with complete Korea Ever-Power documentation from scratch. Submit your report for review or enquire about a new production order.
Gear analyser (all teeth) · CMM · Material cert (EN 10204 3.1/3.2) · Hardness survey · MPI · Standard on every order
Editor: Cxm
