- [Instructor] Before we begin modeling our Spur gear,
let's go over some of the main equations that we'll need.
As you recall, the module is the measure of the tooth size
for metric gears.
It's calculated by dividing the pitch circle diameter
by the number of teeth.
Based on your knowns and unknowns,
you can also manipulate the same equation
to calculate the number of teeth
if you knew what the pitch circle diameter
and the module were.
And if you know the module and number of teeth,
you can use the same equation to calculate
the pitch circle diameter.
The center point distance between two mating gears
is simply the two gears respective pitch diameters
added together and divided by two.
The outer diameter is calculated by taking the number
of teeth, adding two and then multiplying it by the module.
The circular pitch is simply PI times our module.
The circular tooth thickness
is our circular pitch divided by two
and then minus the circumferential backlash.
For this course, we're going to simply assume
that the circumferential backlash is equal to 0.3 times
our module.
There are many industrial standards that outline
how you properly calculate the backlash for your gear
based on many environmental factors.
But that is beyond the scope of this course.
Note that if you're measuring the distance between the teeth
you add the backlash rather than subtract it.
The equation for our whole tooth depth
will vary based on the value of our module.
If the module is less than 1.25,
the whole tooth depth will be 2.4 times our module.
If the module is equal to or greater than 1.25,
the tooth depth will be equal to 2.25 times our module.
This will allow for sufficient clearance
as the gear increases in size.
And lastly, the addendum is simply equal to our module.
And the dedendum is calculated by subtracting the module
from the tooth dept.
This has been a quick overview of the metrics Spur gear
equations that we're going to use to model our gear.