In this video we will learn

how to design spur gears.

Here we will learn the design of spur gears for its

mechanical strength, for dynamic loading conditions, and finally

for surface durability.

We will meet all the design requirements conforming to

the AGMA standard.

In a really simplified manner.

So, let's get into it.

Before starting the design will have the following design requirements.

or design inputs.

Here the gear should be able to transform an angular velocity to another angular velocity

RPM1 to RPM2

and it should transmit a specified amount of power

also there will be some space constraints

so this design should be able to meet that also

And most of the time

material of design is an input to the designer

So using this design data, the designer has to find out

The following gear parameters such as

Number of teeth on both the gears

Pitch circle diameter

addendum and dedundum

face width

and tooth thickness

so these are the outputs we are expecting from a gear design

so lets see how we can deduce values from this input data

We will start the design by considering the space limitation constraint

the designer cant design a gear of any size

if he does so there can be two problems.

First, the gear may not be economical at all

Second, the gear may not get fit into the space which is supposed to get fit

so there is a space constraint when designing the gears

Assume the desired gear should go within the desired area. Something like this.

So the designer cannot xxxx say

if some this diameters of these two gears

they should less than the allowed width,

say eigthy percent of the allowed witdth

so this is one equation

And we also know the speed ratio of the gear

so we can write another equation like this

Next step, determination

of number of teeth on each gear

first step, you have to assume

a number of teeth t one for small gear

here, I should say something to you: desing

is an open ended problem

there can be many solutions for a single

problem and all of them can be right

according to your first assumption

the design may change but

you have to star like this

if you know t one you can find out

number of teeth on second gear using this relation

and this ..

diametal pitch

Now we got the number of teeth on both of gears

but still there is a small issue

it has to be checked for

The issue of interference

Interference means if

your gear has got profile below base circle

that won't be involute shape

so if this portion of the gear comes in contact

with the meshing gear it can

cause material erosion and huge problems of noise

but you could avoid this interference

if following conditions are satisfied

if number of teeth are more ....greater than

this value then

there won't be any interference

So for check for this

if this conditions is true evertything

is perfect you've got number of teeth in both gears

but if this condition is wrong

then you have increase value of t1

and have to redo this calculation again

and here aw means addendum value

and xxxx per xxx of gear

and usually sin of phi takes 20 degres

in that case you can take addedum of one module

and deddendum one point two module

and module is defined like this

Next, design for strength of gear

or your gear should able to withstand

the force acting on the gear

here, if there is a force acting on the gear

the gears has two components one: tangential

and one radial

the tangential ....induce a bending stress

over the xxx of the gear

and if the maximum value is bending stress induced over here

is more than the allowed stress limit

the gear will fail

you can avoid this can of failures

by designing with help of

an equation call Lewis bending equation

before preceding to the Lewis bending equation we

should determine tangential force first

you know tangential force at gear multiplied by xx velocity

And you know the power transmitted

so you can solve for Ft

Now, according to Lewis bending equation

maximum bending stress induced over here

will be this