Gear

Define Inference When Increased

terminologies

A symmetric gear tooth has

Symmetric identical profiles on both sides of Load Carrying Side Equal on both
__
gear tooth the tooth (pressure and non- sides(bidirectional loads)
pressure side).

An asymmetric gear tooth has Optimized for unidirectional loads.

Asymmetric
different profiles on the pressure Stronger pressure side & weaker non- __
gear tooth
and non-pressure sides. pressure side

Larger teeth, resulting from an increased normal

Tooth thickness & reference diameter are
module, provide greater bending strength and
influenced by module.
Module is the ratio of the pitch load-carrying capacity. This allows the gear to
diameter to the number of teeth handle higher torques.
Normal module measured perpendicular
(m = d/t)
to the helical tooth surface (normal to the
Normal A larger normal module naturally leads to larger
tooth profile).
module(tooth The normal module (mn) overall gear dimensions.
profile) essentially defines the tooth size.
The normal module defines the size of the
Very large teeth can sometimes contribute to
teeth.
A larger normal module means increased noise levels.
larger teeth, and a smaller normal
For manufacturing reasons, most helical
module means smaller teeth. Larger teeth provide a coarser tooth pattern
gears currently manufactured are of the
normal type.
More robust gears and size, cost, load capacity
 The helix angle is the angle A larger helix angle increases the overlap of
between the tooth helix and the For most applications: 15° to 30°. tooth contact, resulting in a higher contact ratio.
gear axis. It's what distinguishes This leads to smoother and quieter operation.
helical gears from spur gears. Helical gears have higher load carrying
capacities than spur gears because their A significant consequence of a larger helix
The helix angle determines the contact ratios are larger than those of spur angle is an increase in axial thrust forces. This
inclination of the gear teeth gears. requires the use of thrust bearings to handle
relative to the gear axis. these forces.
Helix angle
Increasing the helix angle β results in an
It is a measure of how the gear increase in the axial force Fa. The increased contact ratio distributes the load
teeth are arranged in a helical over a larger area, enhancing the gear's load-
path along the gear’s Thus, one of the disadvantages of carrying capacity.
circumference. increasing the helix angle is the increase of
axial forces on the helical gear The gradual engagement of helical teeth,
Helical gear as high load capacity mechanism. facilitated by a larger helix angle, reduces noise
due to their contact ratio are and vibration.
larger than spur gear.
A larger pressure angle results in a wider tooth
root, making the teeth stronger and better able
The pressure angle is the angle to withstand higher loads.
between the line of action (the
14.5° for smooth and high contact ratio.Increasing the pressure angle reduces the
direction of the force transmitted
between meshing teeth) and a likelihood of undercutting, a condition that
Pressure 20° balance between strength and smooth weakens the tooth base, especially in gears with
line tangent to the pitch circle.
angle(ϕ) operation. fewer teeth.
Common pressure angle 14.5° ,
25° High-load applications (e.g., heavy A higher pressure angle increases the radial
20° & 25°.
machinery, high-torque applications) force exerted on the bearings, which may
In some cases 22.5° & 17.5° require stronger bearings.

In some cases, a higher pressure angle can

contribute to increased gear noise.
 For involute gears, an increase in center
distance results in an increase of the operating
pressure angle.

Backlash, the clearance between meshing

teeth, tends to increase.This can lead to less
precise motion transmission.

The contact ratio, which indicates the average

Centre The center distance (C) is the number of teeth in contact, might decrease.This
a = (d1 + d2) / 2
distance distance between the centers of can affect the smoothness and load-carrying
two meshing gears. capacity of the gears.

According to research, the stress generated on

gear teeth is increased when the operating
center distance increases.

if the center distance is increased too much, the

gears will not mesh deeply enough, and this will
cause problems with proper functionality.
 More teeth in contact at any given time lead to
a higher contact ratio, resulting in smoother and
quieter operation.This reduces vibration and
noise.
Affects pitch diameter and center
distance. A greater number of teeth distributes the load
more evenly, reducing stress on individual teeth
More teeth provide smoother operation and increasing the gear's load-carrying
but increase manufacturing complexity. capacity.
Number of The total number of teeth on a
Fewer teeth can cause undercutting in Increasing the number of teeth allows for finer
teeth gear.
small gears. speed adjustments and more precise motion
transmission.
The number of teeth on the driving and
driven gears directly determines the gear Increasing the number of teeth reduces the risk
ratio, which affects the speed and torque of undercutting, which is a condition that
transmission. weakens the tooth base, especially in smaller
gears.

increasing the number of teeth will increase the

overall size of the gear.
 A tween meshing teeth, allowing the gear to
distribute the load over a larger area and
enhances the gear's ability to handle higher
It is the width of the gear tooth loads and torques.
measured parallel to its axis.
By distributing the load over a wider area, the
A wider face width improves load
The face width is the width of the bending stress on individual teeth is reduced,
distribution and strength.
gear tooth measured along the which improves the gear's durability and
Facewidth(b) gear axis. resistance to fatigue failure.
Excessive face width can cause
misalignment and uneven load sharing.
In gears, it plays a vital role in A larger face width helps to even out the load
determining the contact area distribution along the tooth, minimizing stress
between meshing teeth. concentrations and promoting smoother
operation.

increasing the face width results in a larger and

heavier gear.

A positive shift thickens the tooth root,

enhancing its resistance to bending stress and
increasing load-carrying capacity.
The profile shift, also known as
Positive shift increases tooth thickness and
addendum modification, involves
reduces undercut. It helps to prevent undercutting, a condition that
displacing the gear cutting tool
weakens the tooth base, especially in gears with
radially from its standard position.
Negative shift decreases tooth thickness a small number of teeth.
Profile Shift and may cause interference.
The profile shift coefficient is a
coefficient
dimensionless value that
Profile shifting can be used to adjust the center
represents the amount of this
A dimensionless factor representing the distance between gears without changing the
displacement relative to the
intentional shifting of the gear profile to gear ratio.
module.
control tooth thickness and strength.
It can influence the contact ratio and sliding
velocities, potentially leading to smoother
operation.
 A higher coefficient means a proportionally
thicker rim, leading to greater resistance to
deformation and failure under load.
Affects gear strength and resistance to
Instead of just stating the rim breakage. The rim provides better support for the gear
thickness in millimeters or inches, teeth, reducing stress concentrations and
it's often expressed as a ratio to Too thin a rim increases the risk of gear improving load distribution.
the gear's module failure.
Rim thickness
This is particularly crucial in high-load
coefficient(C)
Coefficient helps engineers ensure Using a coefficient allows for scaling the applications. A thicker rim minimizes the risk of
that the rim has sufficient strength rim thickness based on the gear's size and the rim itself fracturing.
relative to the size of the gear operating conditions.
teeth. A thicker rim will dampen vibrations better than
Trim = m x C : Trim ≥1.2×(dedendum). a thinner rim.

Increasing the thickness of the rim will add

weight to the gear.

A larger ID removes more material from the

center of the gear, resulting in a lighter
component.

Must match the shaft size for proper A larger ID reduces the gear's rotational inertia,
The diameter of the inner bore of fitment. making it easier to accelerate and decelerate.
Inner This is advantageous in high-speed or dynamic
the gear, where it mounts onto the
diameter(di) applications.
shaft. Affects gear weight and structural
strength.
If the inner diameter becomes too large, the
remaining hub of the gear becomes weaker. This
can lead to failure of the hub, especially under
high torque loads.
 Increasing the inner rim diameter, while keeping
the outer diameter constant, directly reduces
The diameter of the rim’s inner Determines the gear’s structural integrity. the rim thickness.
surface, excluding the gear teeth.
Inner diameter A thicker rim provides better support but A thinner rim leads to decreased rigidity, making
of gear This diameter defines the increases weight. the gear more susceptible to deformation under
rim(dbi) boundary between the gear teeth load.
and the supporting structure (web It directly influences the rim thickness and
or hub). the overall stiffness of the gear. Reduced rim thickness can result in higher stress
concentrations at the tooth root, increasing the
risk of fatigue failure.

Its thickness determines how well the gear A thicker web provides greater rigidity, reducing
can resist deformation and transmit deflection and deformation under load. This
The thickness of the web torque. helps maintain proper tooth engagement and
connecting the gear hub to the minimizes stress concentrations.
rim. Affects gear rigidity and vibration
Web damping. A thicker web enhances the gear's ability to
thickness(bs) The web is the part of the gear transmit torque efficiently, reducing torsional
that bridges the gap between the Too thin a web may cause gear deflection.
rim and the hub. deformation under load.
Increased web thickness can dampen
The web thickness is critical for the vibrations, leading to quieter and smoother
structural integrity of the web and its ability operation.
to support the gear teeth. A higher factor signifies a thicker web relative to
the face width, leading to increased gear
rigidity. This reduces deformation under load.
It is a ratio that compares the web This factor helps engineers understand the
thickness (bs) to the face width (b) proportion of web thickness relative to the
A thicker web provides better support,
of the gear. gear's face width.
Web thickness distributing loads more evenly and minimizing
factor(bs/b) stress concentrations.
Factor allows for scaling the web A higher factor indicates a relatively
thickness based on the gear's size, thicker web, while a lower factor indicates
The gear can transmit torque more effectively
load, and material. a relatively thinner web.
with reduced torsional deflection.

Increased web thickness contributes to better

 Runout causes variations in the gear's rotational
velocity, leading to increased vibration and
Toothing runout, also known as
noise during operation.
gear tooth runout or simply runout, It's a form of gear error that can arise from
refers to the variation in the radial manufacturing imperfections, mounting
The load is not evenly distributed across the gear
distance of the gear teeth from inaccuracies, or damage.
Toothing teeth, resulting in higher stress concentrations on
the gear's axis of rotation.
runout(docum certain teeth. This can lead to premature wear
Higher runout reduces accuracy and
entation only) and failure.
it's a measure of how much the increases noise.
teeth "wobble" or deviate from a
Runout negatively impacts the gear's ability to
perfectly concentric circle as the Precision manufacturing minimizes runout.
provide precise motion transmission.
gear rotates.
The uneven loading that runout causes, will
The standardized profile used as a increase the wear of the gear teeth.
base for gear design. Determines tooth shape, strength, and
Select meshing behavior.
The reference profile defines the Effects of increasing the nomenclulature like root
reference
basic shape of the gear tooth, radius, addendum, and dedendum.
profile Common profiles include full-depth
including parameters like root involute and stub-tooth profiles.
radius, addendum, and
dedendum.

A deeper dedendum leads to a thicker tooth

root, enhancing its resistance to bending stress.
This increases the gear's load-carrying capacity.
A ratio determining the depth of
the tooth space below the pitch Affects root strength and clearance
A larger dedendum provides more clearance
circle. between meshing gears.
Dedendum between the tip of one tooth and the root of the
coefficient mating tooth. (app.: debris or thermal
used in conjunction with the Higher dedendum increases the risk of
expansion)
normal module to calculate the tooth bending failure.
dedendum.
Although the added clearance normally
prevents interference, under very high loads, the
gear can deflect enough to cause interference.
 A larger coefficient results in a larger root
radius.
A larger root radius distributes stress more evenly,
A factor defining the curvature at
Larger root radii reduce stress minimizing stress concentrations at the tooth
the base of the gear teeth.
concentration and improve fatigue root. This significantly increases the gear's
Root radius resistance. resistance to fatigue failure.
The root radius coefficient helps to
coefficient
standardize this radius in relation
Small root radii may cause stress risers and The transition from the tooth flank to the root is
to other gear dimensions, often
early failure. much smoother, reducing the chance of cracks
the module.
starting.
FEA is commonly used to optimize the root
radius and ensure adequate strength.

Positively influence the contact ratio, leading to

smoother operation.
Addendum
the addendum coefficient, in Affects contact ratio and gear meshing.
coefficient( It allows for adjustments to the center distance
conjunction with the module,
Addendum between gears without altering the gear ratio.
determines the height of the gear Too high an addendum can cause
modification
tooth above the pitch circle. excessive interference.
coefficient) Decrease in the tip thickness of the gear tooth.

https://sci-hub.st/10.3390/mca1010036

A larger protuberance provides more clearance

for the shaving or grinding tool, preventing
Defines the height of the
interference and improving the quality of the
protuberance on the gear tooth
finished tooth profile.
profile. Affects machining and the final tooth
Protuberance
shape.
height Minimizes the risk of interference between the tip
The protuberance height
coefficient of the mating gear and the root of the gear
coefficient defines the height of Helps in avoiding undercutting.
being machined.
this intentional undercut, relative
to the normal module.
Increasing protuberance height, will change the
active depth of the gear tooth.
 The angle of the extra material at A larger angle provides more clearance for the
the base of the gear tooth. shaving or grinding tool, reducing the risk of
interference.
The protuberance angle defines Ensures smooth cutting during gear
Protuberance the angle of the protuberance manufacturing. If the angle is too large, it can lead to excessive
angle relief relative to the tooth flank. material removal, weakening the tooth root.
Controls chip flow and reduces tool wear.
The angle effects the shape of the blended area
between the root radius and the gear flank.

A higher coefficient can lead to an increased

contact ratio, resulting in smoother and quieter
operation.
Helps reduce stress concentration and
Determines the rounding or noise.
Tip form height adjustments to the center distance between
chamfering at the tip of the gear
coefficient gears without changing the gear ratio.
tooth. Too much chamfering can reduce tooth
engagement area.
Increasing the tip form height coefficient, or
positive profile shift, decreases the thickness of
the tooth tip. This can weaken the tip.
 A chambered involute involves
creating a slight concavity or
"chamber" in the tooth profile, Affects contact stress and load
Larger angle creates a more pronounced
typically near the tooth tip. distribution.
chamber, providing greater clearance between
the tooth tips of meshing gears.
This modification is primarily used Helps in noise reduction and smooth
to reduce tip interference and meshing.
Minimizes the risk of tip interference, especially
improve contact characteristics,
Profile angle of under load or misalignment, which can lead to
especially under load and Creating chamber involute profiles
the chamber noise, vibration, and premature wear.
misalignment. requires more precise manufacturing
involute
techniques and tooling.
Excessive chambering can reduce the effective
The "profile angle" in this context
contact ratio, which might negatively impact
refers to the angle of the smoothing out the engagement and
smoothness and load-carrying capacity.
chambered section relative to the disengagement of teeth, variations in the
standard involute profile. profile angle can reduce noise and
vibration.
The angle defining the chamber
or relief at the tooth profile.

Generating Forming Process

Process Casting (Sand, Die,
Hobbing Investment)
Shaping
Milling Forging (Open Die, Closed
The method used to manufacture
Determines gear accuracy, durability, and Broaching Die)
the gear (hobbing, shaping,
Manufacturing surface finish. Grinding
grinding, etc.):
process Shaving Powder Metallurgy
Generating process & forming
Affects cost and production time. Honing (Sintering)
process
Lapping
 Reduces stress concentration and
The point where profile Moving the start of modification further up the
increases gear life.
modifications (like tip relief) begin tooth flank increases the extent of the root relief.
at the root.
Start of Poor modification placement can lead to
(OR) Provide more clearance for the mating gear or
modification excessive wear.
The point along the tooth profile manufacturing tools.
at root
where the intentional deviation
Finite element analysis (FEA) is crucial for
from the standard involute profile Start of modification upwards, changes the
optimizing the location of the modification
begins in the root region. active profile of the gear tooth.
and ensuring adequate strength.

The point along the tooth height

Increasing the height coefficient changes the
where modifications begin. Controls load distribution across the gear
Start of active profile of the gear tooth.
teeth.
modification
Standardized way to define the
at height Higher coefficient means the modification
starting point of root fillets, Poorly designed modifications can reduce
coefficient extends further up the tooth flank, increasing the
protuberances, or other gear efficiency.
amount of relief or undercut.
modifications.

Refers to the specific diameter at

which the intended deviation from Modification (e.g., root fillet) will extend further
the standard involute tooth profile up the tooth flank, increasing the amount of
initiates in the root region. material affected.
Alters gear engagement characteristics.
Start of
modification Radial measurement, indicating Excessive modification can remove too much
Reduces noise and impact forces during
at diameter where the modification starts material, potentially weakening the tooth root.
meshing.
along the tooth's height.
Improve stress distribution in the root area,
The diameter at which gear profile reducing stress concentrations.
modifications begin.
 Affects cutting accuracy and final gear
profile.

increase in the tool's tip height, or a positive

Defines the height of the tool’s tip, Incorrect values may lead to incomplete
tooth formation. profile shift of the tool, generally results in a
affecting the final gear tooth
thinner tooth tip
shape.
Tool's tip form Coefficient is inherently tied to the gear
height manufacturing process, specifically the Plays a role in preventing undercutting,
Coefficient determines the
coefficient especially in gears with fewer teeth.
specific shape and height of the design of the cutting tool.
cutting tool's tip, relative to the
normal module. altering this coefficient is often carried out Changes to the tool's tip shape affect the gear's
by using profile shifting techniques on the contact ratio
gear cutting tools.

A factor defining how much of the Larger addendum can increase the contact
tool’s profile extends above the ratio, leading to smoother operation.
Affects the addendum of the final gear.
Tool's pitch line.
addendum Increasing the addendum coefficient will often
Ensures correct engagement of meshing
coefficient Coefficient, when multiplied by result in a thinner tip thickness of the gear tooth.
gears.
the normal module, determines
the addendum of the cutting tool. increase the active depth of the gear tooth.

Gear teeth produced will have a larger root

Affects root strength and stress
radius
Radius directly translates to the concentration.
root radius of the gear teeth being
Larger root radius distributes stress more evenly,
Tool's tip radius cut. A larger radius reduces fatigue failure risk.
minimizing stress concentrations at the tooth
coefficient
root.
The radius of the tool tip, affecting Critical parameter for controlling stress
the final root radius of the gear. concentration and fatigue strength at the
larger radius creates a smoother transition from
tooth root.
the tooth flank to the root.
 Affects backlash and meshing accuracy.
Tooth thickness tolerance defines Looser tolerances lead to greater variations in
the permissible variation in the Too much variation can lead to poor load tooth thickness, resulting in increased backlash.
actual tooth thickness from the distribution and increased wear.
Tooth thickness nominal (design) value. Greater variations in tooth thickness can cause
tolerance Precise control improves gear noise and uneven load distribution and increased noise
The permissible variation in the longevity. and vibration during operation.
thickness of a gear tooth due to
manufacturing tolerances. Tighter tolerances mean less variation, and looser tolerances increase backlash
looser tolerances mean more variation

Tooth thickness allowance is a

planned deviation from the
nominal tooth thickness. Ensures proper final fit after finishing.
primary effect, A larger positive allowance
increases the clearance between meshing
It's used to create or adjust Helps in achieving correct backlash after
Tooth thickness teeth.
backlash, or to compensate for material removal.
allowance
known variations.
Increased backlash reduces the risk of binding or
If excessive, it reduces gear strength and
seizing
The intentional reduction in tooth load-carrying capacity.
thickness to accommodate
finishing processes like grinding.
 increase in the measured base tangent length
compared to the nominal value suggests that
base tangent length is the
Used for gear inspection to measure tooth the teeth are thicker than intended
distance measured over a specific
spacing accuracy.
number of teeth, along a tangent
Thicker teeth can lead to reduced backlash, or
to the base circle.
Base tangent Directly related to pitch accuracy and even interference, which can cause binding or
length transmission error. seizing.
The length of a straight line
tangent to the base circle of the
Affects gear rolling motion and tooth thickness can lead to uneven load
gear across a specific number of
smoothness. distribution, resulting in increased stress on
teeth.
certain teeth

Theoretically, the backlash should be zero,

Normal backlash in helical gears is but in actual practice some backlash must
the clearance between meshing be allowed to prevent jamming of the
teeth measured along the normal teeth due to tooth errors and thermal More clearance reduces the risk of binding or
plane (perpendicular to the tooth expansion. seizing, especially due to thermal expansion or
helix). contamination.
Reduces binding and allows for
Normal The clearance between mating lubrication. Excessive backlash can lead to increased noise
backlash gear teeth measured along the and vibration as the teeth impact each other
normal to the tooth surface. Too much backlash leads to vibration and during direction changes.
noise.
Normal backlash is the amount of Increased backlash reduces the precision of
play or clearance between Essential to allow for lubrication, thermal motion transmission.
meshing teeth in the normal expansion, and manufacturing tolerances.
direction.
 Circumferential backlash in helical
gears is the clearance between
meshing teeth measured along
the pitch circle in the transverse More clearance reduces the risk of binding or
Affects motion accuracy and load
plane (the plane perpendicular to seizing, especially due to thermal expansion or
transmission.
the gear axis). contamination.
Circumferentia Higher values increase shock loads and
The arc distance between mating Excessive backlash can lead to increased noise
l backlash noise.
gear teeth measured along the and vibration as the teeth impact each other
pitch circle. during direction changes.
Lower values risk interference and gear
locking.
It is the difference between the
tooth space and the tooth
thickness, as measured along the
pitch circle.

larger positive allowance increases the

Prevents excessive rounding or material clearance between meshing teeth, contributing
Tip diameter allowance is a
loss during grinding. to increased backlash.
planned deviation from the
nominal tip diameter.
Tip diameter Controls tooth tip strength and contact smaller tip diameter reduces the risk of tip
allowance pattern. interference with the mating gear.
The extra material left at the tip of
the gear tooth to compensate for
Affects contact stress and wear Reducing the tip diameter can reduce the
finishing operations.
characteristics. effective contact ratio and gear tooth tip
thickness
 Ensures correct root radius formation after
Root diameter allowance is a
machining.
planned deviation from the root diameter allowance can reduce the
nominal root diameter. thickness of the tooth root
Root diameter Helps reduce stress concentration at the
allowance root.
The extra material left at the root root diameter is changed, the web thickness of
of the gear tooth before final the gear will also be changed.
If incorrect, it can lead to premature tooth
finishing.
failure due to fatigue.

The number of teeth over which a

Spanning more teeth makes the measurement
measuring instrument (such as a closely tied to measurements like base
more sensitive to cumulative errors in tooth
micrometer or span gauge) takes tangent length and span measurement.
spacing and profile.
measurements to determine gear
Number of accuracy. used to assess the accuracy of tooth
span measurement will change proportionally to
teeth spanned spacing and profile.
the number of teeth spanned
defines the number of teeth
included in a measurement, number of teeth spanned is a critical
base tangent length will change proportionally
typically for quality control or parameter in quality control inspections.
to the number of teeth spanned.
inspection.

Diameter of the balls or pins used Larger balls/pins will change the calculated
in measurement devices to check critical parameter for span measurement tooth thickness.
tooth thickness or span. and similar techniques.
Diameter of larger diameter changes the contact point
ball/pin The diameter of a ball or pin used diameter is carefully chosen to make between the ball/pin and the tooth flank.
to measure the span of gear accurate contact with the gear tooth
teeth, typically for checking tooth flanks. larger diameter changes the contact point
thickness or base tangent length. between the ball/pin and the tooth flank.
 larger tolerance allows for greater variations in
center distance, which directly translates to
It accounts for manufacturing errors in the increased backlash.
The permissible variation in center
Centre gear housing or mounting.
distance between two meshing
distance tooth contact due to center distance variations
gears due to manufacturing
tolerance It directly influences backlash and tooth can lead to increased noise and vibration.
tolerances.
contact.
location and size of the tooth contact pattern
will be less consistant.

primary effect, Increasing the center distance

directly increases backlash (backlash can lead
The intentional adjustment to the to increased noise and vibration)
Centre center distance to compensate
primary effect. Increasing the center
distance for thermal expansion, load operating pressure angle will increase, affecting
distance directly increases backlash.
allowance deflection, or manufacturing tooth forces and contact patterns.
variations.
contact ratio may decrease, potentially
affecting smoothness.

Thicker teeth reduce the clearance between

meshing gears, resulting in decreased backlash.

Tooth thickness refers to the width It's a critical factor in determining Measurements such as span measurements, or
Tooth thickness of a gear tooth measured along backlash, load capacity, and contact ball/pin measurements over teeth will be
the pitch circle. characteristics. affected.

tooth thickness becomes excessive, friction and

heat generation can increase.
 The gear that transmits power in a
Driving gear
gear pair (usually the input gear).

The flank (side surface) of a gear

Working flank
tooth that transmits load during
Gear
operation.

The rotational movement of a

Gear direction gear (clockwise or
of rotation counterclockwise) based on its
meshing with another gear.

The expected operational lifespan

Required
of a gear before failure or major
service life
maintenance.

Factors representing stress at the

Factors, root,
root (bending stress) and flank
flank
(contact stress) of a gear tooth.
A severe form of gear wear
caused by high surface friction
Scuffling
and temperature, leading to
material transfer between teeth.
A type of gear failure where
Tooth flank
cracks develop and propagate
fracture
on the flank surface of the tooth.
 A standard gear used for
Reference
comparison in gear inspections
gear
and calibrations.

The designed operating speed of

Nominal speed
the gear system in RPM
|n1|
(revolutions per minute).

The expected torque transmitted

Nominal
by the gear system under normal
torque |T1|
conditions.

Nominal The power transmitted through the

power |P| gear system

Tiny surface fatigue cracks forming

Micropitting due to high contact stress and
poor lubrication.

Gear failure originating below the

Subsurface tooth surface due to cyclic
fatigue loading.
Effect:

The probability that a gear

Reliability operates without failure for its
designed lifespan.
 A safety factor accounting for
Application
load variations and real operating
factor
conditions.

A correction factor that accounts

Dynamic
for dynamic forces during gear
factor
operation.

The ratio of actual load to nominal

Transverse
load acting in the transverse
load factor
direction of gear teeth.

Mesh load A factor considering variations in

factor load during gear meshing.

Alternating The stress factor considering cyclic

bending factor bending loads on gear teeth.

Face load Accounts for load variation across

factor the facewidth of the gear.

Flank line Adjustments made to the tooth

modification flank to improve load distribution.

Position of
The area where gear teeth
contact
contact during meshing.
pattern
When Decreased Diagram

__

__

Smaller teeth result in reduced bending strength

and load-carrying capacity.

A smaller normal module allows for more

compact gear designs.

Smaller teeth can, in some instances, lead to

smoother and quieter operation, particularly at
higher speeds.

Smoothless and contact ratio increases

A smaller helix angle reduces the overlap of tooth
contact, leading to a lower contact ratio.

A smaller helix angle reduces the axial thrust

forces, lessening the burden on bearings.

The reduced contact ratio can lead to a

decrease in the gear's load-carrying capacity.

less overlap of the teeth can lead to more noise.

A smaller pressure angle results in a narrower

tooth root, reducing the tooth's load-carrying
capacity.

Decreasing the pressure angle, increases the risk

of undercutting, particularly in gears with fewer
teeth.

A lower pressure angle reduces the radial force

on the bearings.

Lower pressure angles can contribute to smoother

and quieter gear operation.
Backlash decreases, which can be beneficial for
precision but can also lead to binding or seizing if
the clearance becomes too small.

The decrease of the center distance causes a

decrease in the operating pressure angle.

If the center distance decreases too much, the

gears might not rotate.
Fewer teeth result in a lower contact ratio, which
can lead to increased noise and vibration.

With fewer teeth, the load is concentrated on a

smaller number of teeth, potentially reducing the
gear's load-carrying capacity.

Decreasing the number of teeth, especially in

small gears, increases the risk of undercutting.

Fewer teeth allow for smaller, more compact

gear designs.

fewer teeth result in larger speed increments.

A narrower face width reduces the contact area,
leading to a decrease in the gear's ability to
handle high loads.

The load is concentrated on a smaller area,

resulting in higher bending stress on the teeth,
which can increase the risk of failure.

concentrating the load can increase wear on the

gear teeth.

A narrower face width allows for a more

compact and lighter gear design, which can be
advantageous in space-constrained applications.

A negative shift thins the tooth root, reducing its

bending strength and load capacity.

It increases the likelihood of undercutting,

particularly in gears with fewer teeth.

Similar to positive shifts, negative shifts can also be

used to adjust center distances.

Negative shifts will also change the contact ratio,

and sliding velocities.
A lower coefficient means a thinner rim, making
the gear more susceptible to deformation and
failure, especially under high loads.

The rim may not provide adequate support,

leading to higher stress concentrations at the
tooth root.

In extreme cases, a very thin rim can fracture

before the gear teeth fail, leading to catastrophic
failure.

A thinner rim will not dampen vibrations as well.

Decreasing the thickness of the rim will decrease

the weight of the gear.

A smaller ID increases the strength and rigidity of

the gear's hub, making it better able to withstand
high torques and loads.

A smaller ID increases the gear's rotational inertia,

making it more resistant to changes in speed.

A smaller ID results in a heavier gear.

More material is used in the manufacturing of the

gear.
Decreasing the inner rim diameter increases the
rim thickness.

A thicker rim provides greater rigidity, reducing

deformation under load.

A more rigid rim distributes loads more evenly,

minimizing stress on individual teeth.

Increased rim thickness can dampen vibrations,

leading to quieter operation.

The primary advantage is a reduction in gear

weight, which can be beneficial in weight-
constrained applications.

A thinner web results in reduced rigidity, making

the gear more susceptible to deformation and
deflection.

A thinner web can lead to increased torsional

deflection, reducing the gear's ability to transmit
torque effectively.

A
A less
lowerrigid webmeans
factor can amplify vibrations,
a thinner leading
web, making theto
gear more prone to deformation.

The web provides less support, potentially leading

to uneven load distribution and stress
concentrations.

Torsional deflection may increase, reducing the

gear's ability to transmit torque efficiently.

A thinner web can amplify vibrations, resulting in

increased noise.
Reduced runout minimizes vibration and noise,
resulting in smoother and quieter gear operation.

The load is more evenly distributed across the

gear teeth, reducing stress concentrations and
extending gear life.

Reduced runout improves the gear's ability to

provide precise motion transmission.

Evenly distributed loads, decrease wear, and

increase the life of the gear.

Effects of increasing the nomenclulature like root

radius, addendum, and dedendum.

A shallower dedendum results in a thinner tooth

root, reducing its bending strength and load
capacity.

Decreasing the dedendum can also increase the

likelyhood of undercut, especially in gears with
low tooth counts.

Increase the risk of interference or binding

A smaller root radius concentrates stress at the
tooth root, increasing the risk of fatigue failure.

The gear tooth is weakened, reducing its load-

carrying capacity.

Increased stress concentrations lead to a shorter

fatigue life.

A negative shift thins the tooth root, reducing its

bending strength.

increase to the tip thickness of the gear tooth.

Provides a means of adjusting center distance.

Decreasing the protuberance height increases

the strength of the tooth root.

Smaller protuberance can lead to interference

between the shaving or grinding tool and the
gear tooth, resulting in poor surface finish or
damage.
A smaller angle reduces the clearance for the
finishing tool, increasing the risk of interference.

The angle effects the shape of the blended area

between the root radius and the gear flank.

A lower coefficient can reduce the contact ratio,

potentially leading to increased noise and
vibration.

Increases the likelihood of undercutting.

Decreasing the tip form height coefficient, or

negative profile shift, increases the thickness of
the tooth tip.
Smaller angle reduces the clearance provided by
the chamber.

increases the likelihood of tip interference,

especially under load or misalignment.

Chamber changes the effective involute profile

of the gear tooth.

The "reference profile" selection directly relates to

the precision of the tooth shape. Generating
processes are essential for achieving the
accuracy required for involute gear profiles.

Forming processes create the general shape, but

they do not provide the level of accuracy
needed for the tooth profile itself. Gears
produced by forming processes often require
further machining (generating) to achieve the
desired involute profile.
Start of modification closer to the root base
reduces the extent of the root relief.

Modification is a root fillet, reducing its extent can

increase stress concentrations.

Reduce clearance for the mating gear or

manufacturing tools.

lower coefficient means the modification is more

localized near the root base.

Decreasing the height coefficient changes the

active profile of the gear tooth.

Less material removal can result in a potentially

stronger tooth root.

Transition is too abrupt, it can increase stress

concentrations.
increases the risk of undercutting.

changes the contact ratio of the produced gear.

affects center distance adjustments.

reduce the contact ratio, potentially leading to

increased noise and vibration.

Shorter teeth reduce the risk of interference.

thicker tip thickness of the gear tooth.

change the root geometry of the gear tooth.

smaller radius may slightly reduce tool wear.

gear teeth produced will have a smaller root

radius.
Tighter tolerances result in more consistent tooth
thickness, reducing backlash.

More consistent tooth thickness leads to smoother

operation and reduced noise and vibration.

tight tolerances can lead to binding or seizing if

there are any thermal expansions or debris
present.

reduces the clearance between meshing teeth.

Reduced backlash improves the precision of

motion transmission.

Decreased backlash increases the risk of binding

or seizing, especially in applications with thermal
expansion or contamination.
decrease in the measured base tangent length
suggests that the teeth are thinner than intended.

Increased backlash reduces the precision of

motion transmission.

base tangent length can point to errors in the

gear manufacturing process.

Reduced backlash improves the precision of

motion transmission.

Decreased backlash increases the risk of binding

or seizing, especially in applications with thermal
expansion or contamination.

backlash is too tight, it can increase wear due to

excessive contact pressure and insufficient
lubrication.
backlash is too tight, it can increase wear due to
excessive contact pressure

Decreased backlash increases the risk of binding

or seizing

reduces the clearance between meshing teeth,

decreasing backlash

tip diameter, changes the active depth of the

gear tooth.
root diameter allowance, changes the
dedendum of the gear.

smaller allowance can result in a thicker tooth

root, potentially increasing its strength.

measured base tangent length will change

proportionally to the number of teeth spanned.

span measurement will change proportionally to

the number of teeth spanned.

smaller ball/pin diameter will result in a different

span measurement value. The measured value
will be smaller.

diameter of the ball or pin is changed, the

calculations used to determine tooth thickness, or
other gear parameters, must also be changed.
tighter tolerance results in more consistent center
distance, leading to reduced and more
predictable backlash.

operating pressure angle will remain closer to the

designed value.

contact ratio will be more stable, resulting in

smoother operation.

Tighter tolerances require more precise

manufacturing, which increases cost.

reduces the clearance between meshing teeth.

reduces the clearance between meshing teeth

contact ratio may increase.

Thinner teeth increase the clearance between

meshing gears, resulting in increased backlash.

Thinner teeth have reduced load capacity.