Contract gear cutting: how to find a specialist machine shop in France
Contract gear cutting addresses a specific need: producing tooth profiles that meet a defined ISO quality grade, on production runs that are often too short to justify investment in dedicated machine tools. Before approaching a machine shop, it pays to master the technical vocabulary of the field, know which capabilities to demand, and prepare a specification document that can generate a usable quote from the very first inquiry.
What is gear cutting and when does outsourcing make sense?
Gear cutting covers all machining operations that create a tooth form — a succession of teeth, profile by profile — on a rough or pre-machined blank. It differs from general turning or milling in that it involves kinematics specific to the generation or forming of involute profiles.
Outsourcing to a subcontractor becomes the logical choice in several situations:
- Prototypes or short runs that cannot justify the purchase of a dedicated hobbing or shaping machine.
- Modules or dimensions outside the range covered by in-house tooling.
- Demanding materials (case-hardening steel, stainless steel, titanium alloys) requiring combined thermal and machining expertise.
- High ISO 1328 quality grades (grades 5 to 7 and above) calling for up-to-date machines and systematic coordinate measurement.
End-user sectors are numerous: aerospace, defence, agricultural machinery, food processing, industrial robotics, and energy. Each imposes its own requirements in terms of traceability, material, and dimensional tolerance.
Gear cutting processes to understand before contacting a machine shop
Understanding the different processes allows for an informed conversation with a subcontractor and helps assess whether their technology suits the part to be produced.
Generation processes: hobbing and gear shaping
Hobbing is the most widely used process for spur and helical cylindrical gears. The hob — a multi-tooth helical tool — generates the involute profile by combining its own rotation with axial feed and the synchronised rotation of the blank. It is a continuous, fast process well suited to medium-volume runs and large modules.
Gear shaping uses a cutter in the form of a gear or pinion that reciprocates axially while rotating in phase with the workpiece. It is particularly suited to internal gears, ring gears with internal teeth, and shouldered pinions whose geometry prevents a hob from passing through.
Form milling
Form milling uses a profiled cutter — whose profile matches the tooth space exactly — to machine one tooth at a time with indexed division between each pass. Less productive than generation processes, it remains relevant for prototypes, one-off repairs, or very large-module teeth that are difficult to generate.
Gear shaving and finishing
Gear shaving is a finishing operation involving very light material removal, carried out before heat treatment. It achieves high ISO 1328 quality grades and corrects profile or helix errors left by rough cutting. After heat treatment (case hardening, nitriding), gear grinding takes over for the most demanding quality grades.
Technical capabilities to require from a specialist subcontractor
Machine inventory and module range
The first question to ask concerns the range of modules covered. A versatile precision engineering shop typically handles modules 1 to 8; a specialist in large transmissions may reach module 20 and beyond. Also verify the maximum workpiece diameter accepted on the gear cutting machines, the maximum centre distance, and the machinable face width.
Machinable materials
Case-hardening steel (16NiCr6, 18CrNiMo7-6) accounts for the majority of transmission gears, but some sectors require stainless steel (food processing, medical) or non-ferrous alloys (bronze, brass for low-load or quiet applications). Confirm that the shop has the experience and cutting parameters suited to the chosen material.
Heat treatment: in-house or through qualified partners
A full-service subcontractor controls the complete chain: rough cutting, shaving, heat treatment (case hardening, quenching, tempering), and gear grinding. If not, the shop must have a network of qualified partners for these operations, with logistics managed carefully to avoid distortion during transfers.
Metrology and quality control
Full coordinate inspection of the gear — profile, helix, pitch, runout, total pitch error — is non-negotiable for ISO grades 5 to 7. Ask whether the shop has a dedicated gear measuring machine, separate from a general-purpose CMM. Inspection reports must be transferable and usable for incoming inspection.
Selection criteria for a gear cutting shop in France
France's industrial landscape includes specialist shops spread across several historically established precision engineering regions. Auvergne-Rhône-Alpes — with clusters in Lyon, Annecy, Saint-Étienne, and Oyonnax — has a high concentration of precision machining subcontractors. Other areas such as Besançon (watchmaking and fine mechanics), Clermont-Ferrand (automotive and agricultural suppliers), and Bordeaux also offer recognised gear cutting expertise.
Beyond geographical location, the key selection criteria are:
- Verifiable sector references: a shop working for the aerospace industry demonstrates documentary and metrological rigour that translates well to other demanding applications.
- Quoting responsiveness: a response time of fewer than five working days on a complete quote is an indicator of commercial maturity and technical readiness.
- Rapid prototyping capability: for engineering teams, the ability to produce a pilot part before series production is often a deciding factor.
- Material traceability: material certificates (EN 10204 3.1 or 3.2), batch marking, and archived manufacturing records.
How to prepare and submit your specification document
An incomplete file is the primary cause of back-and-forth exchanges, extended lead times, and misinterpretation. The following data are the minimum required for any cylindrical gear:
Mandatory geometric data
- Module (m) and number of teeth (z) — these two parameters define the pitch.
- Normal pressure angle (typically 20°, sometimes 14.5° or 25° depending on the application).
- Helix angle for a helical gear (and hand of helix: right or left).
- Face width, pitch diameter, tip diameter, and root diameter.
- Profile shift coefficient (x) if applicable.
Quality and treatment data
- Target ISO 1328 quality grade (profile, helix, pitch).
- Material designation and grade, delivery condition of the blank.
- Required heat treatment: type, case depth, core and surface hardness in HRC or HV.
- Tooth flank surface finish (Ra or Rz on the flank).
- Required finish after the operation (shaved, ground, or as-cut).
Always attach the fully dimensioned drawing in its native CAD format (STEP, IGES) and as a locked PDF, along with the operation routing if it has been defined on the engineering side.
Points to watch: lead times, tolerances, and quality control
Delivery lead times depend directly on the shop's machine loading, the availability of the correct tooling (hob or shaping cutter at the exact required module), and the heat treatment cycle. For a standard part in module 3 to 6, a lead time of three to six weeks in normal production is reasonable; allow more for rare modules or very high ISO grades requiring post-treatment grinding.
On tolerances, non-conformities can easily go undetected if inspection is limited to a simple gauge check or column measurement. Requiring a full gear inspection report — profile and helix traces, pitch deviation table, total cumulative pitch error — protects both parties and secures the goods-inward process.
Relevant certifications and standards in gear cutting
ISO 1328 defines the accuracy grades for cylindrical gears (from grade 1, the most precise, to grade 12). It is the standard reference for communication between the engineering office and the machine shop. AGMA 2000 remains common for projects destined for the North American market.
On the shop certification side, ISO 9001 is the minimum expected baseline. For aerospace work, EN 9100 is frequently required. In the defence sector, specific approvals (DGA, NATO) may apply. Certain food processing sectors additionally impose enhanced material traceability and the exclusion of mineral-based lubricants from any indirect contact with foodstuffs.
In precision engineering, the chosen ISO 1328 grade directly determines the admissible process: grade 8 can often be achieved by hobbing and shaving alone, whereas grade 5 will require gear grinding after heat treatment, with a significant impact on both cost and lead time.
Frequently asked questions
What is the difference between a spur gear and a helical gear?
A spur gear has teeth parallel to the axis of rotation. A helical gear has teeth inclined at a helix angle relative to that axis. The helix increases the contact ratio — several teeth are in contact simultaneously — which reduces noise and improves load capacity, at the cost of an axial thrust force that must be absorbed by the bearings.
How do I choose between generation processes and form milling?
Generation processes (hobbing or shaping) are preferred as soon as the batch exceeds a few parts or the required ISO quality grade is high, since they produce precise and repeatable involute profiles. Form milling suits one-off parts, prototypes, or very large modules where generation is less straightforward. It is slower and less accurate as standard, but sufficient for low-demand applications.
What information is essential in a specification for gear cutting?
Module, number of teeth, pressure angle, helix angle (for helical gears), face width, ISO 1328 quality grade, material grade, required heat treatment, and flank surface finish are the minimum data. Without these elements, the machine shop can neither price the job accurately nor guarantee conformance of the delivered part.
Is gear shaving always necessary before heat treatment?
No. Shaving is only relevant when the target quality grade before heat treatment is incompatible with the as-cut condition, or when profile errors need to be corrected in anticipation of quench distortion. For moderate ISO grades (8 to 10) and parts with low distortion risk, direct cutting followed by heat treatment may be sufficient, particularly if gear grinding is performed as the finishing operation.
Which French industrial regions are known for contract gear cutting?
Auvergne-Rhône-Alpes accounts for a large share of specialist shops, with clusters in Lyon, Annecy, Saint-Étienne, and Oyonnax. Besançon has a long-standing association with fine precision mechanics. Clermont-Ferrand and Bordeaux also have capable shops, often linked to their regional automotive and aerospace supply chains. The final selection should nevertheless be based on actual technical capabilities rather than location alone.