Custom Gear RFQ Checklist: What Engineers Should Provide for an Accurate Quote | SMM - Shanghai Michigan Mechanical
Official Website: michiganmech.com
Custom gears are rarely difficult because of one dimension alone.
A gear that looks straightforward on a drawing may involve multiple manufacturing considerations: gear geometry, material condition, heat treatment, distortion, datum selection, machining sequence, gear accuracy, inspection capability, tooling, and production volume.
For this reason, an accurate custom gear quotation should be more than a price based on material weight and machining time. Before quoting, the manufacturer should understand what the gear must do, how it can be manufactured, how it will be inspected, and what risks need to be controlled before production begins.
At Shanghai Michigan Mechanical (SMM), we work with customers on custom gears, shafts, racks and other precision power-transmission components from prototype through production. A complete RFQ helps our engineering and sourcing teams evaluate manufacturability, select an appropriate process route, identify technical risks, and provide a more reliable quotation.
This guide explains what information is most useful when requesting a quotation for a custom gear.
1. What Is Custom Gear Manufacturing?
Custom gear manufacturing is the production of gears designed for a specific application rather than selected from a standard catalog.
These may include:
Spur gears
Helical gears
Internal gears
Bevel and spiral bevel gears
Miter gears
Worm gears and worm wheels
Gear racks
Splined shafts and geared shafts
Small-module and precision gears
Other special gear geometries
The appropriate manufacturing process depends on the gear geometry, material, size, accuracy, quantity and application.
Depending on these requirements, a manufacturing route may begin with bar stock, forgings, castings or other near-net-shape blanks. Gear teeth may be produced by hobbing, shaping, milling, skiving, grinding or other specialized processes.
Heat treatment may include carburizing, induction hardening, nitriding, through hardening, precipitation hardening or other processes depending on the material and performance requirements.
There is therefore no single "best" manufacturing process for every custom gear.
The objective is to select a process that can consistently achieve the required function, quality, cost and production volume.
2. What Information Is Needed to Quote a Custom Gear?
The more complete the RFQ package, the more accurately a manufacturer can evaluate feasibility, cost and lead time.
For most custom gear projects, we recommend providing the following information.
RFQ Information
Why It Matters
2D technical drawing
Defines dimensions, tolerances, GD&T, datums and inspection requirements
3D CAD model
Helps review geometry and manufacturability
Gear type and gear data
Defines the required tooth geometry
Mating gear information
Helps verify center distance, backlash and mating conditions
Material
Determines machining, heat treatment and raw-material strategy
Heat treatment
Affects hardness, case depth, distortion and finishing
Gear quality/accuracy
Determines manufacturing and inspection processes
Surface finish
May require grinding or other finishing operations
Prototype quantity
Influences tooling and process selection
Production quantity / EAU
Helps determine the appropriate production method
Application information
Helps engineers understand the design intent
Speed and torque
Useful when reviewing gear performance requirements
Documentation requirements
Determines inspection and quality-documentation scope
Not every project requires every item.
However, missing information should be identified and clarified before production, rather than interpreted by the manufacturer.
3. What Gear Data Should Be Included?
A gear drawing should clearly define the tooth geometry.
Depending on the gear type, important information may include:
Number of teeth
Module or diametral pitch
Pressure angle
Helix angle
Hand of helix
Pitch diameter
Outside diameter
Root diameter, where required
Profile shift/addendum modification, where applicable
Backlash requirements
Tooth thickness or measurement-over-pins/balls requirements
Gear accuracy grade
Tooth flank surface finish
Tooth profile or lead modifications, if required
For helical gears, the helix angle and hand should be clearly identified.
For mating gear sets, providing information for both gears is highly recommended.
This allows the engineering team to evaluate the relationship between the two components rather than reviewing each gear independently.
4. Why Is the 2D Drawing Still Important?
A 3D model is extremely useful for understanding part geometry, but for precision gear manufacturing it does not always contain all the information required for production and inspection.
The approved 2D drawing is typically the primary technical reference for:
Dimensional tolerances
GD&T
Datum structure
Gear accuracy
Surface finish
Material
Heat treatment
Hardness and case depth
Inspection requirements
Special notes and acceptance criteria
For example, a 3D model may show a bore and gear teeth perfectly concentric, but it does not necessarily tell the manufacturer the allowable runout between them.
That tolerance can significantly affect the manufacturing sequence, fixturing, inspection method and cost.
When both 2D drawings and 3D models are provided, any discrepancy between them should be clarified before manufacturing rather than interpreted by the supplier.
5. Material and Heat Treatment Matter as Much as Tooth Geometry
Gear performance depends on more than the shape of the teeth.
Material selection and heat treatment can significantly affect:
Load capacity
Wear resistance
Fatigue life
Impact resistance
Dimensional stability
Machinability
Manufacturing cost
Depending on the application, custom gears may use carburizing steels, alloy steels, stainless steels, precipitation-hardening stainless steels, bearing steels, engineering plastics and other materials.
Typical heat-treatment routes may include:
Carburizing and quenching
Used when a hard, wear-resistant case and tougher core are required.
Nitriding
Provides a hard surface layer with relatively low overall distortion and is useful for certain alloy-steel applications.
Induction hardening
Allows localized surface hardening and can be appropriate for selected gear geometries and production requirements.
Through hardening / quench and tempering
May be appropriate where the required properties do not call for a separate hardened case.
The correct material and heat-treatment route should therefore be selected based on the application and drawing requirements, not simply because a particular material or process is commonly used for gears.
6. Prototype vs. Production: Why Quantity Changes the Manufacturing Strategy
This is one of the most important pieces of information in a custom gear RFQ.
A manufacturing method that makes sense for 2 prototype gears may not be economical for 2,000 production gears per year.
For prototype quantities, the manufacturer may intentionally select a process requiring less dedicated tooling, even if the unit machining cost is higher.
For larger production quantities, it may become economical to invest in:
Forging or near-net-shape blanks
Dedicated cutting tools
Fixtures
Inspection gauges
Automated machining
Optimized heat-treatment batches
Dedicated process controls
For this reason, we recommend providing both:
Prototype / initial order quantity
and
Estimated Annual Usage (EAU)
when requesting a quotation.
This allows the manufacturer to evaluate not only the lowest prototype price, but also a realistic production strategy.
7. What Our Engineers Review Before Quoting a Custom Gear
A professional quotation should not begin with price.
It should begin with feasibility.
Before quoting a custom gear, an engineering review may consider:
Gear Geometry
Can the specified geometry be manufactured using an appropriate and stable process?
Are there unusual tooth forms, undercut risks, very thin tooth tips or other geometric constraints?
Gear Accuracy
Can the specified quality grade be achieved by hobbing or shaping, or will grinding or another finishing process be required?
A higher accuracy grade can significantly change the manufacturing route and cost.
Datum and Runout Requirements
What features control gear concentricity?
Can the gear teeth, bore, journals and other critical features be manufactured and inspected from a consistent datum structure?
Material Condition
Is the specified material readily available in the required form and size?
Should the blank be produced from bar stock, forging or another starting form?
Heat-Treatment Distortion
Carburizing, quenching and other thermal processes can cause dimensional changes.
Critical dimensions and tolerances should therefore be evaluated together with the heat-treatment sequence.
Tooth Modifications
Does the drawing require profile or lead modifications such as:
Tip relief
Root relief
Crowning
End relief
Lead modification
Profile modification
Tooth-tip chamfering or rounding
These features may require specific manufacturing and inspection capabilities.
Tooling and Fixturing
Are special cutters, fixtures, mandrels or inspection gauges required?
If so, these should be identified separately rather than hidden inside the unit price.
Inspection Feasibility
A tolerance is only useful if it can be reliably measured.
Before production, the manufacturer should determine how critical gear and dimensional characteristics will be inspected.
8. How Should Custom Gears Be Inspected?
Inspection requirements should correspond to the drawing and the functional importance of the gear.
Different characteristics require different inspection methods.
Analytical Gear Inspection
A gear measuring center can evaluate characteristics such as:
Profile deviation
Lead/helix deviation
Pitch deviation
Runout
Other gear-quality parameters specified by the applicable standard
Dimensional Inspection
CMMs and conventional dimensional inspection equipment may be used to verify:
Bore diameter
Shaft diameters
Keyways
Hole locations
Face dimensions
Runout
Perpendicularity
Parallelism
Other GD&T requirements
Material and Heat-Treatment Verification
Depending on the drawing, verification may include:
Material certificates
Chemical composition
Hardness
Effective case depth
Core hardness
Microstructure
Nondestructive Testing
Where required:
Magnetic Particle Inspection (MPI) can be used to detect surface and near-surface discontinuities in ferromagnetic components.
Ultrasonic Testing (UT) may be specified when internal material integrity needs to be evaluated.
The inspection plan should be determined by the drawing, application and customer requirements, rather than applying every possible inspection method to every gear.
9. Quality Planning Should Match the Project Risk
Not every custom gear project requires a full automotive APQP or PPAP package.
Quality planning should be proportional to the complexity, production volume, application and customer requirements.
For appropriate projects, quality planning may include:
Design for Manufacturability (DFM) review
Process flow
PFMEA
Control Plan
Work instructions
First Article Inspection
Material traceability
Heat-treatment records
Gear inspection reports
Capability studies
PPAP documentation
Corrective and Preventive Action (CAPA)
The objective is not to generate paperwork.
The objective is to identify important risks before they become production or customer problems.
10. What Documentation Should You Request?
Documentation requirements can have a meaningful impact on both cost and lead time and should therefore be identified during the RFQ stage.
Depending on the project, customers may request:
Material Test Report (MTR)
Certificate of Conformance (COC)
Heat-treatment certificate
Surface-treatment certificate
Dimensional inspection report
Gear inspection report
First Article Inspection Report
PPAP documents
NDT reports
Hardness/case-depth reports
Packaging and traceability records
If special documentation is required, including it in the original RFQ helps prevent surprises after production has already started.
11. A Practical Custom Gear RFQ Checklist
Before sending your next gear RFQ, check whether you have provided:
Engineering
2D drawing
3D STEP model, if available
Complete gear data
Mating gear information, if applicable
GD&T and datum requirements
Gear accuracy requirement
Surface finish requirements
Material & Heat Treatment
Material specification
Material condition
Heat-treatment specification
Surface hardness
Effective case depth, if applicable
Core hardness, if applicable
Production
Prototype quantity
Production order quantity
Estimated annual usage
Required delivery date
Application
Gear application
Operating speed
Torque/load
Duty cycle, where relevant
Environmental conditions, where relevant
Quality
Inspection requirements
Material certification requirements
Gear inspection report requirements
FAI / PPAP requirements, if applicable
Special traceability requirements
If some of this information is not yet available, that does not necessarily prevent an RFQ.
It simply means the missing requirements should be identified as open technical items rather than silently assumed.
12. What If You Only Have a 3D Model or a Physical Sample?
Not every project begins with a complete production drawing.
For legacy components, replacement gears and reverse-engineering projects, customers may have only:
A physical sample
An incomplete drawing
A 3D model
Basic application information
In these situations, the first step should be determining what can be reliably established from the available information and what still requires engineering confirmation.
A physical sample can help establish geometry and material characteristics, but it does not automatically reveal the original designer's tolerances, intended backlash, load requirements or acceptance criteria.
Reverse engineering should therefore distinguish between:
what can be measured and what must be defined.
13. The Goal of a Good RFQ Is Not Simply a Fast Price
For custom gears, the lowest initial quotation is not always the lowest final cost.
An incomplete technical review can later result in:
Repeated drawing clarification
Incorrect process selection
Unexpected tooling costs
Heat-treatment distortion
Inspection disputes
Prototype failures
Delivery delays
Rework or scrap
A good RFQ process should reduce these risks before an order is placed.
At SMM, our objective is to understand the drawing, identify manufacturing risks, work with qualified manufacturing resources, and establish a practical manufacturing and inspection plan before moving from quotation to production.
Send Us Your Custom Gear RFQ
If you are developing a new gear, replacing an existing component, or looking for an alternative manufacturing source, send us your available engineering information for review.
For the fastest and most accurate evaluation, please include:
2D drawing + 3D model + quantity/EAU + material + heat treatment + gear accuracy requirements.
If some information is missing, identify what is known and what remains open. Our engineering review can then focus on the areas that require clarification before quotation.
Shanghai Michigan Mechanical
Custom Gears, Shafts & Precision Mechanical Components
SMM
SMM
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