Herringbone gears, also called double helical gears, use two opposite helix directions on the same gear to cancel axial thrust while keeping the smooth running advantage of helical teeth. They are useful for high-load, high-torque, and smoother power transmission, but they are also more difficult to machine, align, and inspect than ordinary spur or single helical gears.
For CNC machining and gear sourcing, the main challenge is not only cutting the teeth. The left-hand and right-hand helix sections must meet correctly, the center groove or apex must be controlled, the gear blank must be accurate, and the final contact pattern must be balanced across both sides.
Key Takeaways
- Herringbone gears combine two opposite helical tooth directions. This helps cancel axial thrust.
- They run smoother than spur gears. Like helical gears, their teeth engage gradually.
- Manufacturing is more complex. Left and right helix alignment, center groove, lead accuracy, and tooth contact must be controlled.
- They are useful for high-load applications. Heavy machinery, marine drives, industrial gearboxes, and high-torque reducers may use double helical gears.
- Inspection must compare both sides. Lead error, contact pattern, runout, backlash, bore accuracy, and FAI are important.
What Are Herringbone Gears?
A herringbone gear is a gear with two sets of helical teeth arranged in opposite directions. The tooth pattern looks like a V shape. This is why it is called herringbone. A double helical gear is similar, but it may include a center groove between the two helix sections for manufacturing clearance.
The main advantage is that the gear keeps the smoother engagement of helical teeth while reducing or canceling the axial thrust that a single helical gear creates. This makes herringbone gears valuable in heavy-duty gearboxes where high load, smooth running, and stable bearing loads are important.
Herringbone Gear vs Helical Gear
| Feature | Single Helical Gear | Herringbone / Double Helical Gear |
|---|---|---|
| Tooth direction | One helix direction | Left and right helix directions on one gear |
| Axial thrust | Creates axial force that bearings must support | Opposite helix sides can balance axial force |
| Manufacturing | Less complex | More complex alignment and tooth cutting |
| Typical use | General gearboxes, reducers, machinery | Heavy-duty, high-load, smoother power transmission |
Why Axial Thrust Cancellation Matters
Single helical gears create force along the shaft axis because their teeth are angled. This axial thrust must be handled by bearings, shoulders, housings, and retaining features. In high-load applications, that force can be significant.
Herringbone gears solve this by using two opposite helix directions. One side pushes one way, and the other side pushes the opposite way. If the gear is designed and manufactured correctly, the axial forces balance. This can reduce bearing load and improve stability in heavy gearboxes.
Manufacturing Challenges
Herringbone gears are harder to manufacture because the two helix sections must align correctly. The center area is especially important. If the left and right teeth do not meet correctly, or if the center groove is not controlled, the gear may run with uneven contact, noise, or load imbalance.
Traditional herringbone gears without a center groove are especially difficult because tool clearance is limited at the center. Double helical gears with a groove are easier to manufacture, but the groove width, face width, lead accuracy, and tooth alignment still need control.
CNC Machining the Gear Blank
Before tooth cutting, the gear blank must be accurate. The bore, faces, OD, hub, shoulders, keyway, and datum surfaces affect the final tooth cutting setup. If the blank has runout or face error, both helix sections can inherit the problem.
For precision blanks, CNC turning and milling prepare the geometry before specialized gear cutting. Bore gauge inspection checks the shaft fit. CMM inspection checks keyways, bolt holes, shoulders, and datum relationships. Runout inspection confirms the gear blank rotates around the intended axis.
Materials and Heat Treatment
Herringbone gears are often used in heavy-duty applications, so alloy steel and heat-treated steel are common. Depending on load and environment, carbon steel, stainless steel, bronze, or other materials may be used. Material choice should consider torque, fatigue life, wear, lubrication, corrosion, and cost.
Heat treatment can improve strength and wear resistance, but it can also distort the gear. For double helical gears, distortion can change lead, runout, and contact pattern on both sides. Final grinding or finishing may be needed after heat treatment for high-accuracy gears. Hardness inspection and final tooth inspection should be included when specified.
Backlash and Contact Pattern
Backlash is still important in herringbone gears. Too much backlash can cause lost motion, noise, and impact. Too little backlash can create heat, binding, and wear. Because there are two helix directions, backlash and contact should be checked across both sides of the gear face.
The contact pattern should be balanced. If one side carries more load than the other, the gear may not achieve the intended thrust cancellation or load sharing. Poor contact pattern can come from lead error, center misalignment, shaft deflection, housing error, or heat treatment distortion.
Inspection for Herringbone Gear Quality
Inspection should confirm both individual geometry and pair performance. Herringbone gears need more than a basic OD and bore check.
- CMM inspection for gear blank datums, keyways, mounting holes, shoulders, and center groove geometry.
- Bore gauge inspection for shaft fit and bearing-related bores.
- Runout inspection for bore-to-tooth and face relationships.
- Lead and helix inspection for left and right tooth directions.
- Center alignment check for the meeting area or center groove.
- Backlash measurement across the working gear pair.
- Contact pattern inspection on both helix sides.
- Surface roughness inspection for tooth flanks and bearing seats.
- FAI before batch production to confirm tooth cutting, heat treatment, and inspection strategy.
Common Herringbone Gear Problems
- Uneven contact between left and right helix sections.
- Center mismatch where the opposing teeth or center groove are not aligned correctly.
- Heat treatment distortion changing lead, runout, or backlash.
- Unexpected axial force because the two helix sides do not balance well.
- Noise or vibration caused by lead error, poor surface finish, or misalignment.
- High inspection cost when the drawing does not define quality requirements clearly.
Design Tips for Herringbone Gear Projects
- Define whether the gear is true herringbone or double helical with a center groove.
- Specify helix angle, hand directions, face width, center groove, and gear quality requirement.
- Control gear blank bore, face runout, OD, and keyway before tooth cutting.
- Plan tooth cutting method and tool clearance before finalizing the design.
- Specify backlash and contact pattern requirements for both helix sides.
- Plan heat treatment allowance and final finishing early.
- Use FAI before batch production for high-load or precision applications.
Related CNC Machining Resources
Herringbone gears connect closely with helical gears, gear blanks, heat treatment, and gear inspection. You may also want to read our guides on helical gears in CNC machining, CNC machined gear blanks, gear accuracy and quality control, and DAXIN’s CNC machining services.
FAQ
What is the purpose of a herringbone gear?
A herringbone gear provides smooth helical tooth engagement while balancing axial thrust through opposite helix directions.
What is the difference between herringbone and double helical gears?
They are closely related. A true herringbone gear may have teeth meeting at the center without a groove, while a double helical gear often has a center groove between the two helix sections.
Are herringbone gears difficult to machine?
Yes. They are more difficult than simple spur or single helical gears because both helix directions and center alignment must be controlled.
Why do herringbone gears reduce axial thrust?
The left-hand and right-hand helix sections generate opposing axial forces. When geometry and loading are balanced, those forces cancel each other.
Final Thoughts
Herringbone gears are powerful but demanding components. They offer smooth high-load transmission and reduced axial thrust, but only when the left and right helical sections are machined, aligned, heat treated, and inspected correctly. For CNC machined gear projects, blank accuracy, center alignment, lead control, backlash, contact pattern, and FAI are the keys to reliable double helical gear performance.