Precision Steering Pinion

Precision Steering Pinion Manufacturing Case

This manufacturing case documents a 20CrMo right-hand helical pinion produced to a customer-controlled drawing. The tooth route uses rough hobbing before carburizing, followed by finish hobbing after carburizing. Tooth geometry, heat treatment, metallurgical acceptance, inspection and tool approval are specific to this released component and are not default specifications for every pinion program.

Verified component specification

• Material: 20CrMo alloy steel according to GB/T 3077, with controlled gear-steel quality, grain size and cleanliness requirements.
• Tooth reference: DIN 3960 and DIN 3961; DIN 8 drawing requirements.
• Tooth geometry: 11 teeth, normal module 1.90110, normal pressure angle 22.5°, right-hand helix angle 20.5°, pitch diameter 22.3260 mm and nominal outside diameter 27.20 mm.
• Tooth generation: Rough hobbing before heat treatment, with machining allowance retained for post-carburizing finish hobbing. Roughing and finishing pinion-tooth generating tools require product-engineering approval for this program.
• Heat treatment: Carburizing, quenching and tempering at 163 ±5°C for at least one hour, according to the controlled project specification.
• Surface hardness: HRC 58–63 after tempering and finishing operations.
• Effective case depth: Minimum 0.6 mm to 86.4 HR15N.
• Total case depth: Maximum 1.4 mm across the complete tooth boundary, including below the roots, as defined by the drawing.
• Traceability and delivery: Burr-free condition, controlled rust prevention and project-specific traceability.

Manufacturing process: rough hobbing, carburizing and finish hobbing

Production starts with verification of the 20CrMo material condition and the controlled metallurgical requirements. Turning, milling, bore preparation and datum machining establish the pinion blank. The 11-tooth right-hand helical form is then rough-hobbed with a defined finishing allowance. The roughing tool, setup and generated tooth condition are reviewed against the approved process before heat treatment.

The rough-hobbed component is carburized, quenched and tempered. The heat-treatment route must control surface hardness, effective and total case depth, network carbides, apparent grain size, retained austenite and quench cracks. After heat treatment, the carburized tooth form is finish-hobbed to recover the specified tooth geometry and DIN 8 deviation limits. The finishing hob and tooth-generation setup are subject to the same product-engineering approval requirement as the roughing tool.

This sequence is important for the case: the first hobbing operation generates the tooth form and leaves controlled stock for distortion and finishing; the second operation is a post-carburizing finish-hobbing step, not a repeat of ordinary soft cutting. Final bore, chamfer and related surfaces are completed according to the released drawing and process plan.

Tooth accuracy and inspection

Final inspection is referenced to the drawing’s DIN 8 requirements and agreed datum system. Key drawing limits include:

• Measurement over two 4.000 mm balls: 30.207–30.257 mm.
• Total pitch deviation: Maximum 0.040 mm.
• Individual pitch deviation: Maximum 0.014 mm.
• Adjacent pitch error: Maximum 0.018 mm.
• Total lead deviation: Maximum 0.020 mm.
• Total profile deviation: Maximum 0.018 mm.
• Radial runout: Maximum 0.029 mm.
• Radial composite error: Maximum 0.035 mm.

Inspection also covers the tooth root and active profile limits, bore and lead-in chamfer condition, surface finish, hardness and case depth. Metallurgical verification includes the customer-defined requirements for carbide condition, grain size, retained austenite and freedom from quench cracks. Material certificates, heat-treatment records, tooth inspection reports, dimensional reports and traceability records are retained or supplied according to the purchasing specification.

Application and quotation boundary

This pinion is presented as a manufacturing example for a steering or transmission program requiring controlled helical-tooth generation before and after carburizing. It does not establish a universal material, module, helix angle, DIN grade or heat-treatment route for other pinions. New programs require independent review of the drawing, standard edition, tooth data, datum system, material, heat treatment, batch size, tool approval and inspection method.

Information required for a similar project

• Released 2D drawing and available 3D model
• Material grade, cleanliness and metallurgical specification
• Module, pressure angle, helix data, tooth count and governing gear standard
• Roughing and finishing stock requirements
• Heat-treatment, hardness and case-depth requirements
• Tooth-deviation limits, datums and inspection-report format
• Prototype quantity, production quantity, annual demand and delivery target

Review our custom gear manufacturing capabilities and quality inspection process. To start a technical review, send the available pinion drawing and project requirements.