This article is part of the CNC Machined Parts Guide: Common Components and How They Are Made on CNX Precision.
CNC gear machining produces toothed components that transmit motion and torque with precise ratios. Gears appear in gearboxes, reducers, robots, and machine tools. Their accuracy decides noise, efficiency, and service life. This guide covers the main machining methods and the DIN and AGMA classes that define quality.
Gears are among the most demanding components a shop can make. The tooth profile, pitch spacing, and surface finish all affect how two gears mesh. A small error in the profile creates noise and vibration. A larger error reduces load capacity and causes early wear. CNX Precision machines spur, helical, and worm gears in one shop.
Why CNC Gear Machining Requires Specialized Equipment
Standard CNC mills cannot cut accurate teeth without dedicated gear tools and software. Gear machining uses specific processes such as hobbing, shaping, broaching, and grinding. Each one creates a different profile and finish.
Every gear program starts with a drawing review. We check module, pressure angle, helix angle, and tooth count against the standard. Small errors here multiply into large problems later.
Tooth accuracy depends on the machine, the tool, and the setup. Gear blanks must be concentric before teeth are cut. Then the cutter must track the blank in a precise timed relationship. Therefore, CNC gear machining combines machine rigidity with gear-specific CAM cycles.
Blank quality is half the battle. A bore that is oval, a face that wobbles, or a shoulder that runs out all move the tooth form. We machine gear blanks to tight concentricity before any tooth cutting begins.
Tool wear changes the tooth form gradually. Therefore, we monitor the hob and shaping cutter with in-process checks. When the profile drifts, we index the tool before the parts leave tolerance.
Gear Machining Methods Compared
Hobbing is the workhorse for external spur and helical gears. A hob cutter rotates while the blank feeds through, generating the tooth form continuously. Hobbing is fast and accurate for medium to large volumes.
Gear shaping uses a reciprocating pinion-shaped cutter. It cuts internal gears, shoulder gears, and cluster gears that hobbing cannot reach. Shaping is slower than hobbing but more flexible.
Shaving is another finishing route for soft gears. A shaving cutter skims a few microns off the flank to improve profile and lead. It costs less than grinding for medium runs.
Broaching pulls a tool through the bore to cut splines and internal teeth in one pass. It suits high-volume parts with consistent shapes. Finally, gear grinding corrects distortion from heat treatment and achieves the highest accuracy classes. In CNC gear machining, the method decides both cost and achievable accuracy.
| Method | Typical Parts | Accuracy | Notes |
|---|---|---|---|
| Hobbing | External spur, helical | DIN 8–6 | Fast, economical |
| Shaping | Internal, shoulder gears | DIN 8–6 | Flexible |
| Broaching | Splines, internal teeth | DIN 7–6 | One-pass, high volume |
| Grinding | Hardened precision gears | DIN 5–3 | Corrects heat distortion |
Lubrication paths and root fillets deserve attention too. Hobbed and shaped gears leave a natural fillet that reduces stress concentration. When the drawing demands a specific root radius, we use form tools or grinding to match it.
Cutting fluid matters for gear quality. It cools the tooth flank, washes away chips, and keeps the cutting edge sharp. We filter the coolant and check its concentration during long runs.
Gear Accuracy Classes: DIN and AGMA
Gear quality in CNC gear machining is graded by standard systems. DIN 3962 classifies tolerances for profile, pitch, and runout. AGMA 2000 uses classes from 3 to 15, where higher numbers mean tighter tolerances. In practice, most industrial gears run AGMA 8 to 10 or DIN 7 to 5. High-speed and aerospace gears need AGMA 12 or better, which normally requires grinding.
Choosing the right class balances cost and performance. A looser class is cheaper to make but noisier. A tighter class costs more but runs smoother. Therefore, specify the class that matches the duty cycle.
The drawing should state the quality class clearly. If it only says “precision gear”, we ask for the standard. That avoids disputes over acceptable profile error and runout.
- AGMA 8–9 / DIN 8–7: general industrial gears.
- AGMA 10 / DIN 6: precision reducers and servos.
- AGMA 12+ / DIN 4–3: aerospace and high-speed.
Measuring the class requires the right instruments. We use gear testers that report profile deviation, pitch error, and runout on a single setup. The report shows exactly which quality level the part meets.
Pin measurement is a quick shop-floor check. Two pins in opposite tooth spaces give a base measurement over pins. That number confirms the tooth thickness without a full gear test.
Materials, Heat Treatment, and Finishing for Gears
Gear material depends on load and speed. 1045 and 4140 steel work for moderate loads. 20MnCr5 and 16MnCr5 case-harden well for automotive gears. Stainless gears suit food and marine duty. Bronze appears in worm wheels, and plastics like POM or PEEK handle light loads quietly.
Heat treatment hardens the teeth. Carburizing adds a hard case and tough core. Induction hardening suits large gears with a simple shape. Nitriding creates a thin, hard surface with minimal distortion. After hardening, grinding restores the profile and finish.
Surface finish on the tooth flank affects efficiency and noise. Hobbed gears typically measure Ra 1.6 µm on the flank. Ground gears reach Ra 0.4 µm or better. For high-speed drives, the smoother flank reduces friction and heat.
Noise control starts with geometry. Profile and lead modifications, such as tip relief and crowning, reduce mesh shock. If your gearbox hums, ask about these modifications during the design phase.
Case depth follows the module. A common rule is case depth at 0.1 to 0.2 times the module, with a hardness of 58 to 62 HRC. We confirm depth by microhardness testing on the first article.
Gear teeth fail in three ways: bending fatigue at the root, pitting on the flank, and wear from contamination. The material, hardness, and finish you choose address one or more of these modes.
CNC Gear Machining FAQ
What is the smallest gear CNC gear machining can produce?
We cut gears down to module 0.5 with hobbing and smaller with wire EDM for prototypes. The practical limit depends on tooth depth and tool availability.
Can you grind gears after heat treatment?
Yes. We grind external spur and helical gears to AGMA 12 and DIN 4 class. Grinding removes distortion and restores the profile after hardening.
Do you supply gear pairs or only single gears?
We machine complete gear pairs and verify the backlash with your center distance. This saves you assembly time and reduces noise risk.
Get a Quote for Your Gear Project
CNC gear machining turns blanks into accurate, quiet, and long-lasting teeth. Choose the method by part geometry, set the DIN or AGMA class by duty, and grind after hardening for the top grades. CNX Precision machines gears, splines, and worm components in steel, stainless, bronze, and plastics. Send your drawing and we will recommend the process and return a quote.
For related information, see our guide to cnc machining service and 5-axis cnc machining and cnc milling vs turning and cnc machining tolerances.