Technical Resources for Gear Buyers
Drawing checklists, material and heat treatment references, accuracy class tables and inspection guidance for gear, rack, sprocket and shaft enquiries.
Most of the time lost between a gear enquiry and a quotation is spent on information that was never on the drawing. These pages collect the reference material we use when we review a drawing, so the enquiry can start from a complete set.
Before you send a drawing
- What a gear drawing has to contain — the parameters that decide price and manufacturability
- Accuracy classes explained — what DIN and GB grades actually measure
- Material and heat treatment reference — which grade for which duty
Product and process references
- Spur and helical gears — geometry, profiles and grinding routes
- Gear racks — joints on long axes and how accuracy accumulates
- Bevel gears — straight versus spiral, and why the pair is the unit of supply
- Worm gears — ratios, efficiency and self-locking
- Sprockets and roller chains — standards and tooth form
- Precision shafts and splines — fits, runout and spline standards
- Custom gear manufacturing — non-standard modules and reverse engineering
- CNC machined parts — housings, flanges and bushings
Gear drawing checklist
A drawing that carries these groups can be quoted without a round of questions.
Tooth geometry — module or diametral pitch, number of teeth, pressure angle, helix angle and hand, tooth thickness or profile shift, tip and root form.
Quality — accuracy class plus the standard it is measured against (DIN, GB, ISO or AGMA), and any special requirement such as backlash range or contact pattern.
Material and treatment — steel grade, heat treatment, surface hardness, case depth where carburised.
Geometry outside the tooth — bore, keyway or spline, hub dimensions, mounting faces, datums, runout limits, surface finish.
Pairing — the mating gear drawing when backlash or centre distance is defined between two parts.
Quantity and stage — prototype, first batch or repeat production.
Accuracy classes
Rack, gear and spline accuracy is stated as a class plus a measured deviation. The class is not a description of quality — it is a set of limits on specific deviations: total profile deviation, total lead deviation, single pitch deviation and total cumulative pitch deviation.
| What the class limits | Where it shows up in service |
|---|---|
| Profile deviation | Contact pattern, noise, load distribution across the tooth |
| Lead deviation | Uneven load across the face width, edge contact |
| Single pitch deviation | Transmission error cycle by cycle, noise at mesh frequency |
| Cumulative pitch error | Position error over a long travel or an index |
Two gears of the same class can behave differently if the deviation sits in different parts of the tolerance band. That is why a report carrying measured values is worth more than a certificate stating conformity.
Material and heat treatment
| Grade | Treatment | Surface | Where it fits |
|---|---|---|---|
| 45# / S45C | Quench and temper | HB 220–250 | General machine parts, light to medium duty |
| 40Cr | Quench and temper; induction hardening for the tooth | HB 240–280; HRC 48–55 induction hardened | Medium load, moderate speed |
| 42CrMo | Quench and temper | HB 280–320 | Heavy load, shock, large sections |
| 20CrMnTi | Carburising and quenching | HRC 58–62 case, HRC 30–42 core | High load with sliding contact, long life |
| ZCuSn10P1 | Cast tin bronze | — | Worm wheels, loaded sliding contact |
Selection follows duty rather than habit: a case-hardened alloy in a light application costs more than it needs to, and mild steel under shock load fails early.
Inspection reports
A report we issue typically covers measured tooth profile, lead and pitch against the drawing’s class; cumulative pitch error over the measuring length; hardness and case depth where heat treatment is specified; surface roughness on ground flanks; and geometry such as runout, straightness or flatness where those are functional.
Where a gear and a mating part are supplied together, the contact pattern check is recorded as well, since backlash and pattern belong to the pair.
Still not sure what to send?
Send the drawing as it stands. An engineer will review it and reply with the specific gaps rather than a request to “provide full specifications”.