Bevel gears transmit power between shafts that meet at an angle — most often 90°. The two common tooth forms in industrial boxes are straight bevel and spiral bevel. This note is generic engineering; for product-level selection see Anand Gears bevel gearboxes (Gleason-type spiral, reduction ratios in the 5:1–50:1 class on the published line) and the comparison with helicals in bevel vs helical.
Geometry in plain language
- Straight bevel — tooth lines are straight generators that would meet at the cone apex. Contact starts abruptly across the full face width when a tooth enters mesh.
- Spiral bevel — tooth lines are curved (spiral). Contact starts at one end of the face and progresses across the tooth, so more than one pair shares load during much of the mesh cycle.
Both forms sit on pitch cones. Shaft axes typically intersect (standard bevels). Hypoid variants offset the axes; they are a separate family and not covered here.
Load capacity
For the same size and material, spiral bevels generally carry higher continuous loads because of gradual engagement and multi-tooth load sharing. Straight bevels remain adequate for lower speeds, intermittent duty, or simple tooling applications where noise is not critical. Axial thrust loads differ with spiral hand and spiral angle — bearings and housing must be designed for that thrust; this is one reason industrial spiral units look more engineered than a simple open miter pair.
Noise and vibration
Straight bevels tend to produce more noise and shock at entry, especially at higher pitch-line speeds. Spiral bevels run smoother and quieter when correctly lapped or cut and properly mounted. If a packaging line or indoor conveyor sits near operators, spiral is usually the default choice for a closed industrial gearbox.
When each is used
- Straight bevel — low-to-moderate speed, hand tools and simple machinery, cost-sensitive open gearing, applications where axial thrust simplification matters more than quiet mesh.
- Spiral bevel — continuous industrial duty, conveyor and material-handling right-angle drives, synchronized multi-jack systems, higher speeds, and any duty where efficiency and noise matter. Anand Gears industrial bevel reducers use this path.
Miter (1:1) sets
A miter gear set is two identical bevels at 1:1 ratio. They change shaft direction (typically 90°) without speed reduction. Miters appear on rail and track equipment, packaging transfers, and jack-shaft networks where only direction — not torque multiplication — is required. Both straight and spiral miters exist; spiral miters are preferred when the shaft runs continuously and noise must stay low. KL-family and similar industrial miters in the Anand Gears product story are spiral bevel units built for this kind of duty.
Efficiency (qualitative)
Spiral bevel mesh is generally more efficient than a high-ratio worm for the same right-angle task — worms trade efficiency for compactness and self-locking behaviour. Between straight and spiral bevels at the same size, spiral usually wins on efficiency and heat once speed rises. Exact efficiency depends on quality, lubrication, and mounting; treat published curves as order-of-magnitude guides, not guarantees.
What to specify on an RFQ
- Shaft angle (usually 90°), ratio or 1:1 miter, and power / torque duty.
- Speed (input RPM) and continuous vs intermittent load.
- Mounting: foot, flange, or shaft-mounted; all dimensions in mm.
- Noise or back-driving requirements (worm may still win if self-lock is mandatory).
Related: Bevel Gearboxes · Bevel vs Helical Gearbox · Contact