How to Source Gears
Gear RFQ checklist: complete gear data table, accuracy grade, material, heat treatment, case depth, bore and keyway, and the inspection that proves it.
318 gear manufacturing companies in the Noramark directory
A gear drawing is two documents in one: the blank (bore, faces, hub, keyway) that a lathe and a mill make, and the teeth, which a hobber, shaper or grinder cuts from the gear data table. Gear shops quote the teeth from that table, so a drawing that shows a tooth outline but no module or diametral pitch, pressure angle, helix angle or accuracy grade cannot be quoted without a phone call.
A good gear RFQ fills in the data table completely, names the accuracy grade the teeth must meet, says how the gear is hardened and where, and states the inspection that proves it. Send the mating gear's data too. Tooth thickness, backlash and center distance only make sense as a pair, and a shop that sees both can catch a mismatch before it cuts steel.
RFQ checklist
17 things to settle on the drawing or in the request before you ask for gear quotes. Print it and tick it off against the print, or copy it into the RFQ.
Gear data
Gear type and hand: spur, helical (left or right hand), bevel, worm and wheel, internal, or spline
Each type runs on different machines. Hand and helix angle must match the mate or the gears will not mesh.
Number of teeth, module or diametral pitch, pressure angle and helix angle
These define the cutting tool. Standard values (20 degree pressure angle, standard modules or pitches) use stock hobs; odd ones need a special hob with its own lead time.
Tooth thickness with tolerance, stated as a measurement over pins or balls or a span measurement
Tooth thickness sets backlash. A measurement over pins or a span gives the shop a number it can check at the machine.
Profile shift (addendum modification), outside diameter and root diameter
Shifted gears are common in compact drives. Without the shift the shop cuts a standard tooth that will not run at your center distance.
Accuracy grade and the standard it refers to: AGMA 2015 or ISO 1328 grade (a lower number is finer) or a legacy AGMA 2000 Q-number (a higher number is finer)
The grade decides whether hobbing alone will do or the teeth must be shaved or ground after heat treatment. The two numbering systems run in opposite directions, and mixing them up is a common, expensive mistake.
Mating gear data and the operating center distance
Backlash and contact depend on the pair. With both, the shop can check for interference and backlash before cutting.
Profile and lead modifications, if any: tip relief, root relief, crowning
Modifications are ground in. They need grinding capability and a clear modification spec to be quoted.
Blank and features
Bore size and tolerance, keyway or internal spline by standard, and any set screw or clamp features
The bore is usually the datum the teeth are cut and checked from, so its tolerance matters as much as the teeth.
Radial runout of the teeth and axial runout of the faces, to the bore or the journals
Gear runout is measured to a datum axis. Naming it makes the shop fixture on the same surface you assemble on.
Face width, hub and web dimensions, tooth-end chamfers and edge breaks
Tooth-end chamfering and deburring are separate operations the shop needs to know about.
Material and heat treatment
Material by grade and spec: for example 8620 for carburizing, 4140 or 4340 for through-hardening, induction hardening or nitriding
Heat treatment is chosen with the material. Carburizing grades have low-carbon cores; nitriding works best on steels with chromium and molybdenum.
Heat treatment: carburize and harden, induction harden (spin or tooth by tooth), nitride, or through-harden, with surface and core hardness
Each process distorts differently and decides whether the teeth must be ground afterwards.
Effective case depth, the hardness it is measured to, and where it applies (flanks, roots, areas left soft)
Case depth is measured to a hardness value, often 50 HRC. Without it the heat treater uses a default that may be too shallow for your load.
Shot peening of the roots, and any finish (black oxide, phosphate, or none)
Root peening raises bending fatigue strength and is a separate vendor step on most jobs.
Inspection and delivery
Inspection: analytical report (profile, lead, pitch, runout), double-flank composite test, or pin measurement only
An analytical report needs a gear measuring machine, and many shops use an outside lab. Name what you need so the price includes it.
Certifications: material cert, heat treat cert with case depth and hardness readings, statement of the grade achieved
Heat treat certs with actual readings are the only record of the case you cannot see.
Quantity, annual volume, and whether gears ship as matched sets
Matched sets are run together, marked and kept together, which adds handling and inspection.
What to send with the RFQ
- A drawing with a complete gear data table, including tooth thickness and accuracy grade.
- The mating gear's data table and the center distance.
- Load, speed and required life, or the rating calculation, if you want the shop to check material and heat treatment.
- A STEP model for the blank. Modeled teeth are reference only; gear shops cut from the data table.
- A sample or the worn gear, for replacements with no drawing.
- Quantity per release and annual usage.
Lead times
| Prototype or first parts | 3-6 weeks for cut gears with standard tooling; 6-10 weeks when heat treatment, grinding or a special hob is needed. |
|---|---|
| Production or repeat orders | 6-12 weeks for heat-treated, ground gears in production lots. A special hob alone can take 4-8 weeks to arrive. |
Typical of U.S. job shops, from order or approved drawing to shipment; confirm with the shop for your part.
What drives the cost
- Accuracy grade: ground teeth cost several times hobbed teeth.
- Special hobs or cutters for non-standard pitches, pressure angles or profile shifts.
- Heat treatment route: carburized gears usually need grinding afterwards; nitrided and induction-hardened gears may not.
- Size and face width: large gears need large machines and long cycle times.
- Inspection: analytical charts on every part versus first pieces only.
- Material: carburizing and aircraft-quality grades cost more and may carry mill minimums.
Common mistakes
- A drawing with drawn teeth and no data table.
- Confusing AGMA 2000 Q-numbers (higher is finer) with AGMA 2015 or ISO 1328 grades (lower is finer).
- A ground-gear grade on a gear that is only hobbed and heat treated, or the reverse.
- No case depth or hardness location on a carburized gear.
- Leaving out the profile shift, so the gear is cut standard and will not run at the design center distance.
- Ordering a replacement from a worn sample without measuring its mate.
Questions to ask the shop
- Which hobs and cutters do you have for this pitch and pressure angle?
- Do you grind teeth in-house, and to what grade?
- Who does the heat treatment, and how do you control distortion?
- What gear inspection equipment do you have, and can you supply analytical charts?
- Can you reverse engineer a gear from a sample, and do you need the mating gear?
Typical processes
Typical materials
Charts and calculators
Frequently asked questions
- What gear quality grade do I need?
- Hobbed or shaped gears without grinding typically reach about ISO 1328 grade 8 to 9 (roughly AGMA 2000 Q8 to Q9), fine for general industrial drives at moderate speed. Quiet, high-speed or heavily loaded gears are usually ground to about grade 6 or finer (roughly Q11 and up). The conversion between systems is approximate. Do not ask for a finer grade than the application needs: each step costs.
- Carburizing, induction hardening or nitriding?
- Carburizing gives the deepest hard case and the highest load capacity, but distorts, so precision carburized gears are ground afterwards. Induction hardening is fast for larger gears and can harden only the teeth, but the pattern at the root needs care. Nitriding gives a thin, very hard case with little distortion, good for finished gears that will not be ground, and suits lighter tooth loads.
- Can a shop make a replacement gear from a worn sample?
- Usually, especially with the mating gear. The shop counts teeth and measures outside diameter, span or pins and helix, then works out module or pitch, pressure angle and profile shift. Wear hides the original tooth thickness, so the mate and the center distance help. Expect a reverse-engineering charge, and approve the derived data table before cutting.
Build the RFQ: attach the print and this checklist
Attach the drawing (PDF) and the model (STEP), and put your answers to the checklist in the description. A Noramark sourcing specialist matches the request with U.S. shops that make gears and contacts you within 1 business day.
