Bevel Gear Manufacturing Guide | Straight & Spiral

Bevel Gear Guide: Straight & Spiral 90° Power Transmission

When two shafts meet at an angle, a bevel gear is usually the answer. Unlike spur or helical gears that connect parallel shafts, bevel gears use conical pitch surfaces and tapered teeth. At Emitech, we help buyers choose the right bevel gear type, process, and material for applications from automotive differentials to aerospace actuators. Understanding these fundamentals lets buyers specify parts that balance performance and cost.

CNC bevel gear cutting and inspection at Emitech's ISO-certified facility in Nanjing, China.

What Is a Bevel Gear?

A bevel gear is a gear whose tooth-bearing surfaces are formed on a cone. The teeth may be straight, spiral, or zerol, and the gear mates with another bevel gear to transfer rotation between shafts that intersect—most often at 90°. The imaginary cone that rolls without slipping against the mating cone is called the pitch cone, and the angle at the cone apex is the pitch cone angle. When two identical bevel gears mesh at 90°, each has a pitch cone angle of 45°; this special case is also called a miter gear and provides a 1:1 speed ratio.

The module (or diametral pitch) of a bevel gear is measured at the large end of the tooth. Face width should not exceed one-third of the cone distance, and the pressure angle is commonly 20°. Because the tooth tapers from heel to toe, cutting and inspection follow a defined tooth line across the cone.

Straight bevel gears have teeth that radiate toward the cone apex. They are easy to design and inspect, but the teeth engage all at once, producing more noise at high speed. Spiral bevel gears have curved teeth that engage progressively, reducing noise, raising load capacity, and smoothing operation at higher speeds. They are preferred in automotive differentials, aerospace gearboxes, and power tools.

Hypoid gears look like spiral bevel gears but have an offset pinion axis, giving a lower driveshaft position and higher contact ratios; they are common in rear-wheel-drive axles.

How We Manufacture Bevel Gears at Emitech

Emitech selects the manufacturing route for each bevel gear based on quantity, precision class, material, and part complexity. We do not force every part onto the same machine. Instead, we compare MIM, CNC machining, powder metallurgy, and conventional gear cutting, then build a process plan that balances unit cost, tooling investment, and lead time.

For prototypes and low volumes, CNC 5-axis milling and Gleason-form cutting cut tooth profiles directly from bar stock without expensive tooling. For medium volumes, CNC gear generators deliver consistent geometry. High-volume production often uses metal injection molding (MIM) or powder metallurgy, followed by sizing or grinding.

After primary forming, most steel bevel gears receive heat treatment and finishing. Carburizing or induction hardening increases surface durability, while profile grinding or lapping corrects distortion and improves mesh quality.

This is why MIM is attractive for small, complex bevel gears at medium-to-high volume: per-piece cost falls once tooling is amortized, and complex 3D shapes can be molded in one operation.

Metal Injection Molding for Bevel Gears

Metal injection molding is a net-shape powder process that combines the design freedom of plastic injection molding with the mechanical properties of wrought or sintered metals. For bevel gears, MIM is especially useful when the gear is small, geometrically complex, and required in quantities large enough to justify a mold investment. Typical MIM bevel gears range from 5 mm to 60 mm in outer diameter, with module 0.3–2.0 and weights from 0.5 g to 50 g.

The MIM process mixes metal powder with a thermoplastic binder, injects it into a precision mold, then debinds and sinters the part. During sintering the gear shrinks uniformly by about 15–20%, so the mold cavity is scaled to compensate. The result is a dense metal bevel gear reaching 95–98% of theoretical density.

MIM holds tight as-sintered tolerances—typically ±0.3% to ±0.5%—so it often eliminates rough cutting for small gears. Critical tooth profiles, bores, and mounting surfaces can be ground, honed, or lapped when higher accuracy is required. This MIM-plus-grinding approach is cost-competitive for automotive sensors, aerospace actuators, and medical devices.

At Emitech, we select MIM for bevel gears when the program calls for thin walls, intricate hub shapes, high annual volume, or material efficiency. Our engineering team reviews tooth geometry for moldability, shrinkage compensation, and sintering support before cutting steel. If you are unsure whether MIM fits your bevel gear project, send us the drawing and we will compare MIM, CNC, and PM options side by side.

Materials & Heat Treatment

Material selection for bevel gears balances strength, wear resistance, corrosion resistance, weight, and cost. The table below lists the most common alloys Emitech uses for straight and spiral bevel gears, along with typical hardness and heat-treatment paths.

Steel bevel gears almost always need heat treatment. Carburizing creates a hard case and tough core, resisting contact and bending fatigue. Induction hardening selectively hardens tooth flanks without distorting the whole part. Stainless and titanium gears use precipitation hardening or solution annealing for strength and corrosion resistance.

Quality Standards & Tolerances

Bevel gear quality is usually specified by ISO 1328-1 for cylindrical and bevel gears, or by AGMA 2000 for North American programs. The standard defines tolerances for single pitch deviation, total cumulative pitch deviation, profile form and slope, helix or spiral angle deviation, and radial runout. Higher grade numbers in ISO 1328 mean tighter tolerances; Grade 4–5 is considered high precision, while Grade 8–10 is commercial quality.

Every bevel gear order starts with a drawing review. We use a CNC gear measuring center for tooth geometry, a CMM for positional tolerances, hardness testers, and surface roughness testers to verify conformance.

Our quality system is ISO 9001:2015 certified, and we support PPAP, FAI, material certifications, and SPC reporting. Dimensional reports include tooth profile, lead, pitch deviation, and runout values.

Bevel Gear Applications Across Industries

Bevel gears appear wherever power must turn a corner. Their compact right-angle layout makes them indispensable in drivelines, gearboxes, and motion-control systems across many sectors.

In the automotive industry, spiral bevel gears are the heart of the differential, transferring torque while allowing speed differentiation during cornering. These gears survive high contact loads and millions of cycles, so they are usually carburized and ground.

Aerospace applications favor lightweight, high-precision bevel gears for flight-control actuators, landing-gear mechanisms, and satellite deployment systems. Materials such as 17-4 PH and Ti-6Al-4V offer strength without excessive weight, while ISO 1328 Grade 5 tolerances ensure reliable motion control. Emitech supplies aerospace MIM components and machined bevel gears with full material traceability.

Power tools use small straight or spiral bevel gears in right-angle drills, grinders, and impact drivers. MIM or powder metallurgy lowers cost in high-volume cordless tools, while CNC machining supports premium pro-grade lines.

Industrial machinery and robotics use bevel gears in indexing tables, right-angle gearboxes, robotic joints, and conveyor drives. Backlash control, repeatability, and long service life are the main priorities.

Medical devices require small, quiet, corrosion-resistant bevel gears for surgical instruments, diagnostic equipment, and drug-delivery systems. 316L and 17-4 PH are common, and MIM enables complex net shapes.

Bevel Gears vs Similar Gear Types

The comparison below clarifies where each gear type fits best.

Spiral bevel gears sit between straight bevel gears and hypoid gears in terms of load capacity and smoothness. They are the default choice for most 90° power-transmission tasks when shafts must intersect. Hypoid gears are selected when higher torque or a lower pinion position is required, while worm gears are chosen for very high reduction or self-locking needs. Selecting the correct gear family early avoids expensive redesign later.

Design Tips & Common Failure Modes

The following design guidelines reflect what Emitech engineers review during every DFM cycle.

Use standard modules and pressure angles. Standard modules such as 0.5, 0.8, 1.0, 1.5, and 2.0 reduce tooling cost, and a 20° pressure angle balances strength and undercut resistance.

Limit face width. Face width should not exceed one-third of the cone distance; wider teeth are harder to cut accurately and can cause uneven load distribution.

Specify generous root fillets. A minimum fillet radius of 0.2 mm reduces stress concentration and improves bending fatigue life.

Control backlash. Precision bevel gear sets often target 0.05–0.15 mm of backlash to balance thermal expansion and positioning accuracy.

Pair material and heat treatment correctly. High-load steel gears should be carburized or induction hardened; corrosion-resistant applications favor 300-series stainless or 17-4 PH.

Frequently Asked Questions

Get a Custom Bevel Gear Quote from Emitech

Whether you need a prototype straight bevel gear or a production run of spiral bevel gears, Emitech has the process portfolio and quality system to deliver. Email yaoqingpu1983@gmail.com or WhatsApp +86 138 1403 4409, or send your drawing for a detailed quote with DFM feedback within 48 hours.