GAWA NI UNO SEND GCASH Gear Nomenclature and Gear Types

Flashcards testing knowledge on spur gear terminology, quantitative equations, sample calculations, and gear classifications from ENGR. Edwin S. Bautista's lecture notes.

What is the definition of a gear?

A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque.

What is a rack and what motion does it produce when meshed with a gear?

A rack is a non-rotating toothed part that meshes with a gear to produce translation (linear motion) instead of rotation.

How are spur gears characterized and mounted?

Spur gears are the most common type of gears, have straight teeth, and are mounted on parallel shafts.

What types of tooth contact occur in spur gears?

Tooth contact in spur gears is primarily rolling, with sliding occurring during engagement and disengagement.

What is the distinction between a pinion and a gear in a mating pair?

A pinion is the smaller of two mating gears, while the larger gear is often called the gear.

How is the pitch circle defined in spur gear nomenclature?

The pitch circle is a theoretical circle upon which all calculations are usually based, and its diameter is the pitch diameter.

What is circular pitch ($p$) and how does it relate to pitch diameter ($d$) and tooth count ($N$)?

Circular pitch ($p$) is the distance measured on the pitch circle from a point on one tooth to a corresponding point on an adjacent tooth. It equals the sum of tooth thickness and width of space, satisfying $p N = \text{π} d$.

What is module ($m$) and what is its standard unit of measurement in SI?

The module ($m$) is the ratio of pitch diameter to the number of teeth ($m = \frac{d}{N}$). Its customary unit of length is the millimeter ($\text{mm}$), serving as the index of tooth size in SI.

What is diametral pitch ($P$) and what units are used for it?

Diametral pitch ($P$) is the ratio of the number of teeth on the gear to the pitch diameter ($P = \frac{N}{d}$). Used only with U.S. units, it is expressed as teeth per inch.

What equations express the relationship between circular pitch ($p$), diametral pitch ($P$), and module ($m$)?

The relationships are $p P = \text{π}$ and $p = \text{π} m$.

What is the difference between addendum ($a$) and dedendum ($b$)?

The addendum ($a$) is the radial distance between the top land and the pitch circle, while the dedendum ($b$) is the radial distance from the bottom land to the pitch circle.

What is clearance ($c$) in spur gear terminology?

Clearance ($c$) is the amount by which the dedendum in a given gear exceeds the addendum of its mating gear.

How is backlash defined in spur gearing?

Backlash is the amount by which the width of a tooth space exceeds the thickness of the engaging tooth measured on the pitch circles.

What formula relates gear ratio and speed ratio to tooth count ($N$), pitch diameter ($d$), and rotational speed ($n$)?

The relationship is given by $\frac{N_g}{N_p} = \frac{d_g}{d_p} = \frac{n_p}{n_g}$, where subscript $p$ represents the pinion and subscript $g$ represents the gear.

What is the formula for the theoretical center-to-center distance ($C$) between two mating spur gears?

The theoretical center-to-center distance is $C = \frac{d_p + d_g}{2}$.

In Example 1, a 17-tooth spur pinion has $P = 8\,\text{teeth/in}$ and runs at $1120\,\text{rev/min}$ driving a gear at $544\,\text{rev/min}$. What are the gear tooth count and center distance?

The number of teeth on the gear is $N_g = 35\,\text{teeth}$ and the theoretical center-to-center distance is $C = 3.25\,\text{in}$.

In Example 2, a 15-tooth spur pinion with $m = 3\,\text{mm}$ runs at $1600\,\text{rev/min}$ driving a 60-tooth gear. What are the speed of the driven gear, circular pitch, and center distance?

The speed of the driven gear is $n_g = 400\,\text{rpm}$, the circular pitch is $p = 9.42\,\text{mm}$, and the center distance is $C = 112.5\,\text{mm}$.

In Example 3, a spur gearset has $m = 4\,\text{mm}$, a velocity ratio of $2.80$, and a 20-tooth pinion. What are the driven gear tooth count, pitch diameters, and center distance?

The driven gear has $N_g = 56\,\text{teeth}$, the pitch diameters are $d_p = 80\,\text{mm}$ and $d_g = 224\,\text{mm}$, and the center-to-center distance is $C = 152\,\text{mm}$.

What is an internal spur gear, what is its larger gear called, and what is an advantage of internal gears?

An internal spur gear has teeth formed on the inner surface of a cylinder or cone. Its larger gear is called an Annular, and internal gears have better load-carrying capacity and are safer because the teeth are guarded.

What are the advantages and design requirements of helical (twisted) spur gears?

Helical gears operate with less noise and vibration than spur gears because load is distributed over several teeth. However, their angular cut creates axial thrust loads, requiring thrust bearings.

How do double helical or herringbone gears resolve the axial thrust problem of single helical gears?

They feature two sets of teeth arranged in a V shape (like mirror-image helical gears stacked together), which cancels out axial thrust because each half thrusts in the opposite direction.

What is the primary drawback of pin gearing?

The distance from the center of each gear to the point of contact changes as the gears rotate, causing the gear ratio and output speed to constantly change (resulting in continuous acceleration and deceleration).

What is the primary function of bevel gears, and at what relative shaft angle are they usually mounted?

Bevel gears are used when the direction of a shaft's rotation needs to be changed, and they are usually mounted on shafts that are $90\,\text{degrees}$ apart.

How are the teeth arranged on a crown gear?

A crown gear's teeth project at exactly right angles to the plane of the wheel, resembling the points on a crown.

How do hypoid gears differ from spiral bevel gears, and where are they typically used?

Hypoid gears are similar to spiral bevel gears except that their shaft centerlines do not intersect. They are typically found in the differential (rear axle) of automobiles.

What rule governs the operation of a worm and worm wheel mechanism?

The worm (a gear with one tooth in the form of a screw thread) always drives the worm wheel (a helical gear), and it never operates in reverse.

What are the objectives and typical applications of non-circular gears?

Non-circular gears are designed for ratio variations and axle displacement oscillations. Common applications include textile machines, potentiometers, and continuously variable transmissions.

What components make up an epicyclic or planetary gearing system?

An epicyclic gearing system consists of one or more outer planet gears revolving around a central sun gear, mounted on a movable arm or carrier, along with an outer ring gear or annulus.

What was the historical function of sun and planet gears during the Industrial Revolution?

Sun and planet gearing was used to convert reciprocating motion into rotary motion in steam engines.

How is a cage gear (lantern gear or lantern pinion) constructed?

A cage gear has cylindrical rods for teeth arranged in a circle parallel to the axle, held together by disks at either end.