Internal Gear Precision Report: Does This “Transmission Heart” Meet the Mark?

Within the factory, gears function as the machinery's very heart, particularly the internal gears. Concealed within the equipment, they silently transmit power; even the slightest deviation in precision can cause the machinery to malfunction—manifesting as excessive noise during operation, increased susceptibility to breakdowns, or even compromising product quality. Today, we shall analyse this report to determine whether this internal gear meets the required standards and can be used with confidence.

First, let's clarify: what sort of internal gear is this?

• Gear Identity Card: This is an internal gear used for precision transmission, with key inspection points being its ‘teeth’ (right flank, left flank) and ‘tooth gaps’ (internal flanks), as these areas are crucial for power transmission;
• Inspection Equipment: Utilised the #1595 specialised machine tool, with ambient temperature maintained at 27.5°C. Temperature control is critical—gears being metallic, thermal expansion and contraction affect dimensions, ensuring measurements taken at a fixed temperature yield accurate results.
• Reference Standards and Tools: Measurements adhered to the German DIN 3962 standard (recognised within the industry as the definitive ‘gear precision specification’). Data analysis employed the professional GearPro v3.17.61 software, effectively performing a ‘CT scan’ on the gear, yielding highly reliable results.

Core Issue 1: Are the gear dimensions correct? Will they fit and turn smoothly?

1. Tooth size — Module: The module is 5.5000mm, simply put, this denotes the thickness of the “teeth” — the larger the module, the sturdier the teeth, enabling greater force transmission. This dimension meets design specifications, indicating it can handle the anticipated power;
2. Core Circle — Pitch Circle: The pitch circle acts as the ‘central track’ for the gear. During transmission, the pitch circles of both gears must mesh and rotate together. The measured pitch circle diameter for this gear is 658.7042mm, matching the design value, ensuring no slippage occurs during rotation;
3. Outer and Inner Circles— Tip Circle and Root Circle: The tip circle diameter is 647.7000mm, while the root circle diameter is 609.8605mm. The difference between these two determines the ‘tooth height’. The measured height is precise, preventing issues where teeth are too short to engage properly or too long to cause jamming.
4. Tooth Width: The tooth width is 130.0000mm. A wider width increases the gear contact area, reducing wear. This width meets the requirements for prolonged operation.
5. Special Angle — Helix Angle: This gear has a helix angle of 118°, meaning the teeth are cut at an angle. This design enables smoother transmission. The report indicates no significant angular deviation, confirming the angle is correct.
6. Indirect Inspection — Pitch: When measuring gears, two standard ‘small rods’ are inserted between teeth to gauge distance (pitch). This gear's standard distance is 637.900mm, with an actual measurement of 635.460mm. The discrepancy falls within permissible limits — indicating uniform tooth spacing without variations in tooth thickness.

Core Issue 2: Is the precision adequate? Does it run smoothly and quietly?

Dimensions being correct is merely the foundation; precision is the key factor determining whether a gear is ‘fit for purpose’.

1. Tooth spacing — pitch error: The distance between each ‘tooth’ must not vary excessively. The report states that the permissible error for a single pitch is 8.0μm (finer than a human hair). Actual measurements mostly fell between 2.5-8.0μm, with a few approaching the upper limit. This is not problematic and will not affect transmission; The more critical ‘cumulative error’ tolerance is 32.0μm. Actual measurements recorded only 10.0μm and 8.0μm, significantly below the standard. This ensures the gear operates smoothly without ‘clunking’ during rotation;
2. Tooth inclination—tooth direction error: Teeth must not deviate excessively along the axial direction. The report indicates LB [%] = -4.8521. Though negative, this falls within acceptable limits, confirming proper tooth alignment. This ensures full contact during transmission, preventing localised wear.
3. Tooth Profile Error: The ‘side curve’ of the teeth must conform to the design specifications to prevent ‘misengagement’. The report indicates no issues with the curve, confirming the tooth profile is acceptable and resulting in minimal noise during rotation.

Conclusion: Approved! Meets high-precision requirements

According to the report, this internal gear meets all dimensional and precision standards, with its cumulative error significantly exceeding requirements, making it a top performer. It is suitable for applications demanding high precision, such as within the joints of industrial robots, precision machine tools, and even auxiliary equipment in aerospace. Not only does it fit and rotate smoothly, but it also operates stably and with exceptional durability. For equipment requiring precise transmission, selecting such a gear is undoubtedly the right choice.