Straight Bevel Gears

What is a Straight Bevel Gear?

A straight bevel gear is a cone-shaped gear with straight teeth. It is often used to transmit power between two axles that are rotating at different speeds. Among all types of conical gears, straight bevel gears are the simplest to produce and the most commonly applied in power transmission across industries.

Construction and Terminology of Straight Bevel Gears

A straight bevel gear has a cone-shaped configuration as its pitch surface and its straight teeth are cut along the cone. The use of different types of bevel gears is not interchangeable and each type of these gears is designed to work in pairs with a mating part.

When it comes to the gear teeth of the straight bevel gears, the main parts include peak, face, flank, bottom, toe, an outer end, and inner end. The pitch line is between the face and the flank of the gears. The heel of a tooth on a bevel gear or pinion is the portion of the tooth surface near its outer end. The toe is the portion that bears the inner end.

The gear teeth of straight bevel gears are straight, but the sides are tapered so that they intersect at a common point is called the cone apex if extended inward. The meshing gears have lined contact. They are not smooth in operation, generating more vibrations and noise at high speeds. Therefore, the application of straight bevel gears is limited to low-speed drives.

The cone-shaped pitch surface of a straight bevel gear is an imaginary toothless surface of averaging the top lands, peaks, bottomland, and valleys of the gear in cross-section. The pitch angle of a straight bevel gear is the angle of the face of the pitch surface and the axis. The shaft angle, on the other hand, is the angle between the axis of the intersection shafts.

Why Use Straight Bevel Gears?

Straight bevel gears are used to transmit power between two non-parallel shafts that intersect. They are commonly used on shafts that intersect at right angles. The direction of rotation of a straight bevel gear is either clockwise or counterclockwise viewing the gear from the back. The main application of bevel gearing is vehicle differential where the direction of the drive shaft turns 90 degrees to drive the wheels. It also has a wide range of use for other industrial applications.

Different Types of Bevel Gears

According to geometry, bevel gears are classified into straight bevel gears, spiral bevel gears, miter bevel gears, Zerol bevel gears, and hypoid bevel gears. Straight bevel gears and spiral bevel gears are the two most fundamental and applicable types. With the tapered nature, all kinds of bevel gears can perform axial thrust onto the support bearings.


Spiral Bevel Gears

Spiral bevel gears have teeth cut in the helical form with the pitch surface being conical. Similar to straight bevel gears, they are installed on shafts whose axes are intersecting. Spiral bevel gears have curved teeth set at an angle to radial lines, which allows the contact to develop gradually and smoothly. This configuration renders more contact length compared to straight bevel gears. They are useful for high-speed applications and others requiring less noise and vibration. However, they are difficult to design and costly to produce as they require specialized and sophisticated machinery to manufacture.


Miter Bevel Gears

Miter bevel gears are gears with chefs positioned at 90 degrees to the mating part that has the exact same number of teeth (1:1 ratio). They come in a straight tooth or spiral gear profile. The main use of miter bevel gears is changing the direction of power transmission without changing speed. However, in the case of spiral miter gear, the twisting directions are different even when the number of teeth is the same. Therefore, it is necessary to pair the right and left-handed pairs in that case.


Zerol Bevel Gears

Zerol bevel gear is a special type of spiral bevel gear where the spiral angle is 0 degrees. The gear teeth of Zerol bevel gears are curved but lie in the same direction as those of the straight bevel gears. Also, the forces acting upon the tooth are the same as those on straight bevel gears. The gears have the characteristics of both straight and spiral bevel gears.

Hypoid Bevel Gears

Hypoid bevel gears are modifications of the spiral bevel gears with the axis offset. The pinion is offset from the gear center, allowing unique configurations and a large diameter shaft. Hypoid bevel gears are typically used for transmitting power between two non-parallel and non-intersecting shafts.

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