# Difference Between Spur Gear And Helical Gear Pdf

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*In the introduction to our gears series we wrote about Backlash and Gear Ratios.*

- The benefits of converting to helical gearing
- Difference Between Spur Gear and Helical Gear
- Helical Gears vs. Spur Gears
- Gears Part 2: 5 Common Gear Types

*Figure On the plane there is a straight line AB, which when wrapped on the base cylinder has a helical trace A 6. See In the plane of rotation, the helical gear tooth is involute and all of the relationships governing spur gears apply to the helical.*

This page lists the standard US nomenclature used in the description of mechanical gear construction and function, together with definitions of the terms. The addendum is the height by which a tooth of a gear projects beyond outside for external, or inside for internal the standard pitch circle or pitch line ; also, the radial distance between the pitch diameter and the outside diameter. Addendum angle in a bevel gear, is the angle between face cone and pitch cone. The addendum circle coincides with the tops of the teeth of a gear and is concentric with the standard reference pitch circle and radially distant from it by the amount of the addendum. For external gears , the addendum circle lies on the outside cylinder while on internal gears the addendum circle lies on the internal cylinder.

## The benefits of converting to helical gearing

The gear teeth act like small levers. The axes may be parallel, intersecting, neither parallel nor intersecting. Here is a brief list of the common forms. We will discuss each in more detail later. Gears for connecting intersecting shafts Straight bevel gears Spiral bevel gears Neither parallel nor intersecting shafts Crossed-helical gears Hypoid gears Worm and wormgear 7.

N 1 N 2 is the common normal of the two profiles. Figure Two gearing tooth profiles Although the two profiles have different velocities V 1 and V 2 at point K , their velocities along N 1 N 2 are equal in both magnitude and direction. Otherwise the two tooth profiles would separate from each other. Therefore, we have or We notice that the intersection of the tangency N 1 N 2 and the line of center O 1 O 2 is point P , and Thus, the relationship between the angular velocities of the driving gear to the driven gear, or velocity ratio , of a pair of mating teeth is Point P is very important to the velocity ratio, and it is called the pitch point.

Pitch point divides the line between the line of centers and its position decides the velocity ratio of the two teeth. The above expression is the fundamental law of gear-tooth action. In this case, the motion transmission between two gears is equivalent to the motion transmission between two imagined slipless cylinders with radius R 1 and R 2 or diameter D 1 and D 2. We can get two circles whose centers are at O 1 and O 2 , and through pitch point P.

These two circle are termed pitch circles. The velocity ratio is equal to the inverse ratio of the diameters of pitch circles. This is the fundamental law of gear-tooth action. The fundamental law of gear-tooth action may now also be stated as follow for gears with fixed center distance Ham 58 : The common normal to the tooth profiles at the point of contact must always pass through a fixed point the pitch point on the line of centers to get a constant velocity ration.

The two profiles which satisfy this requirement are called conjugate profiles. Sometimes, we simply termed the tooth profiles which satisfy the fundamental law of gear-tooth action the conjugate profiles. Although many tooth shapes are possible for which a mating tooth could be designed to satisfy the fundamental law, only two are in general use: the cycloidal and involute profiles.

The involute has important advantages -- it is easy to manufacture and the center distance between a pair of involute gears can be varied without changing the velocity ratio. Thus close tolerances between shaft locations are not required when using the involute profile. We use the word involute because the contour of gear teeth curves inward.

Gears have many terminologies, parameters and principles. One of the important concepts is the velocity ratio, which is the ratio of the rotary velocity of the driver gear to that of the driven gears.

The number of teeth in these gears are 15 and 30, respectively. If the tooth gear is the driving gear and the teeth gear is the driven gear, their velocity ratio is 2. This involute curve is the path traced by a point on a line as the line rolls without slipping on the circumference of a circle. It may also be defined as a path traced by the end of a string which is originally wrapped on a circle when the string is unwrapped from the circle.

The circle from which the involute is derived is called the base circle. In Figure , let line MN roll in the counterclockwise direction on the circumference of a circle without slipping. When the line has reached the position M'N' , its original point of tangent A has reached the position K , having traced the involute curve AK during the motion.

As the motion continues, the point A will trace the involute curve AKC. For any instant, the instantaneous center of the motion of the line is its point of tangent with the circle. Note: We have not defined the term instantaneous center previously. When two bodies have planar relative motion, the instant center is the point at which the bodies are relatively at rest at the instant considered. The normal at any point of an involute is tangent to the base circle.

Because of the property 2 of the involute curve, the motion of the point that is tracing the involute is perpendicular to the line at any instant, and hence the curve traced will also be perpendicular to the line at any instant.

There is no involute curve within the base circle. Figure Spur Gear In the following section, we define many of the terms used in the analysis of spur gears. Some of the terminology has been defined previously but we include them here for completeness. See Ham 58 for more details. Pitch surface : The surface of the imaginary rolling cylinder cone, etc. Pitch circle : A right section of the pitch surface. Addendum circle : A circle bounding the ends of the teeth, in a right section of the gear.

Root or dedendum circle : The circle bounding the spaces between the teeth, in a right section of the gear. Addendum : The radial distance between the pitch circle and the addendum circle. Dedendum : The radial distance between the pitch circle and the root circle.

Clearance : The difference between the dedendum of one gear and the addendum of the mating gear. Face of a tooth : That part of the tooth surface lying outside the pitch surface. Flank of a tooth : The part of the tooth surface lying inside the pitch surface. Circular thickness also called the tooth thickness : The thickness of the tooth measured on the pitch circle.

It is the length of an arc and not the length of a straight line. Tooth space : The distance between adjacent teeth measured on the pitch circle. Backlash : The difference between the circle thickness of one gear and the tooth space of the mating gear. Circular pitch p: The width of a tooth and a space, measured on the pitch circle.

Diametral pitch P: The number of teeth of a gear per inch of its pitch diameter. A toothed gear must have an integral number of teeth. The circular pitch , therefore, equals the pitch circumference divided by the number of teeth. The diametral pitch is, by definition, the number of teeth divided by the pitch diameter.

Module m: Pitch diameter divided by number of teeth. The pitch diameter is usually specified in inches or millimeters; in the former case the module is the inverse of diametral pitch. Fillet : The small radius that connects the profile of a tooth to the root circle. Pinion : The smaller of any pair of mating gears.

The larger of the pair is called simply the gear. Velocity ratio : The ratio of the number of revolutions of the driving or input gear to the number of revolutions of the driven or output gear, in a unit of time.

Pitch point : The point of tangency of the pitch circles of a pair of mating gears. Common tangent : The line tangent to the pitch circle at the pitch point. Line of action : A line normal to a pair of mating tooth profiles at their point of contact. Path of contact : The path traced by the contact point of a pair of tooth profiles.

Pressure angle : The angle between the common normal at the point of tooth contact and the common tangent to the pitch circles. It is also the angle between the line of action and the common tangent. Base circle :An imaginary circle used in involute gearing to generate the involutes that form the tooth profiles.

Table lists the standard tooth system for spur gears. Coarse pitch 2 2. The result is called the base pitch p b , and it is related to the circular pitch p by the equation 7.

Figure Two meshing gears To get a correct meshing, the distance of K 1 K 2 on gear 1 should be the same as the distance of K 1 K 2 on gear 2. As K 1 K 2 on both gears are equal to the base pitch of their gears, respectively. Hence Since and Thus To satisfy the above equation, the pair of meshing gears must satisfy the following condition: 7. Ordinary gear trains have axes, relative to the frame, for all gears comprising the train.

Figure a shows a simple ordinary train in which there is only one gear for each axis. In Figure b a compound ordinary train is seen to be one in which two or more gears may rotate about a single axis.

Figure Ordinary gear trains 7. Also, we know that it is necessary for the to mating gears to have the same diametral pitch so that to satisfy the condition of correct meshing. Thus, we infer that the velocity ratio of a pair of gears is the inverse ratio of their number of teeth. For the ordinary gear trains in Figure a , we have These equations can be combined to give the velocity ratio of the first gear in the train to the last gear: Note: The tooth number in the numerator are those of the driven gears, and the tooth numbers in the denominator belong to the driver gears.

Gear 2 and 3 both drive and are, in turn, driven. Thus, they are called idler gears. Since their tooth numbers cancel, idler gears do not affect the magnitude of the input-output ratio, but they do change the directions of rotation. Note the directional arrows in the figure. Idler gears can also constitute a saving of space and money If gear 1 and 4 meshes directly across a long center distance, their pitch circle will be much larger.

There are two ways to determine the direction of the rotary direction. The first way is to label arrows for each gear as in Figure The second way is to multiple m th power of " -1 " to the general velocity ratio. Where m is the number of pairs of external contact gears internal contact gear pairs do not change the rotary direction. However, the second method cannot be applied to the spatial gear trains. Thus, it is not difficult to get the velocity ratio of the gear train in Figure b : 7.

Thus, they differ from an ordinary train by having a moving axis or axes. Figure shows a basic arrangement that is functional by itself or when used as a part of a more complex system.

## Difference Between Spur Gear and Helical Gear

Mechanical drives are used to transmit motion, torque and power from driver shaft such as prime mover to driven shaft such as machine unit. There are four mechanical drives, namely gear drive, belt drive, chain drive and rope drive. Unlike belt drive a friction drive , gear drive is one engagement drive, which indicates power transmission occurs by means of successive engagement and disengagement of teeth of two gears. It is also a rigid drive as no intermediate flexible element exist between two gears. Here the driver gear mates directly with the corresponding driven gear, and thus it is suitable for power transmission over small distance.

The gear teeth act like small levers. The axes may be parallel, intersecting, neither parallel nor intersecting. Here is a brief list of the common forms. We will discuss each in more detail later. Gears for connecting intersecting shafts Straight bevel gears Spiral bevel gears Neither parallel nor intersecting shafts Crossed-helical gears Hypoid gears Worm and wormgear 7. N 1 N 2 is the common normal of the two profiles. Figure Two gearing tooth profiles Although the two profiles have different velocities V 1 and V 2 at point K , their velocities along N 1 N 2 are equal in both magnitude and direction.

In spur gear, the teeth are parallel to the axis of the gear. In helical gear, teeth are inclined at an angle (called helix angle) with the gear axis. Spur gear imposes only radial load on bearings.

## Helical Gears vs. Spur Gears

Gear types can be classified according to the relative position of their axes of revolution. Spur gears are used in many devices, like the electric screwdriver, wind-up alarm clock, and washing machine. Helical gears, on the other hand, operate much more smoothly and quietly than spur gears.

Involute tooth surfaces are a successful technical solution for both spur and helical gear drives since they provide linear contact and a low-level function of transmission errors under good conditions of meshing. Tip relief is usually required to improve contact conditions during the transfer of meshing between adjacent pairs of teeth. Yet, unfavorable conditions of contact appear when shaft deflections and misalignments are present. Localization of contact through lead crowning is a solution that increases the cost of machining in both spur and helical gear drives.

Gear drive is one important mechanical power transmission element that can transmit power and motion from one shaft to another by means of toothed wheel rigidly mounted on the shafts. It is one engagement drive that indicates power transmission occurs by means of successive engagement and disengagement of teeth of two gears. Whereas the belt drive one type of friction drive is especially suitable for medium to long distance power transmission, gear drive is preferred when distance between two shafts driver and driven is small usually below 0.

### Gears Part 2: 5 Common Gear Types

Spur gears and helical gears are two of the most common types of gears. They can often be used for the same types of applications; so what are the differences between helical gears vs. Spur gears are the most common type of gear, and are also the most simple. They have straight teeth that are produced parallel to the axis of the gear. Since they have the simplest design, they are the easiest to design and manufacture, and are therefore the most economical type of gear.

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PDF format. Spur Gears Helical gears have a smoother operation due to the angle twist creating instant contact with the gear teeth. Machinedesign Com Like spur gears, the normal gear ratio range for straight bevel gears is to

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*По спине Сьюзан пробежал холодок.*

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T he simplest-to-design and the easiest-to-use gearing design is that of the spur gear.

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