- [Instructor] Our first step in creating our gear
is to make a cylindrical blank
that we'll cut away from to create our finished part.
Start by opening up a new part in SolidWorks.
Make sure that the units are set to millimeters,
grams, seconds.
You could also open up the chapter start file
from the course exercise folder.
Our first step will be to create our global variables
for the gears module, pressure angle, bore
and number of teeth.
For this example, we're going to have a module
of one millimeter, pressure angle of 20 degrees,
bore of 10 millimeters and 36 teeth in the gear.
Let's open up our equation window
by clicking the tools dropdown and select the equations.
And we'll enter in our variables here
under the global variable header.
So that is a module of one.
A pressure angle of 20.
A bore of 10
and number of teeth equal to 36.
Okay.
These constants will be the foundation
for a series of equations.
That'll drive the geometry of our gear.
So if we want to change the gear size,
we would only have to modify these variables
and refresh the model.
Hit okay to close out the window.
Now that our global variables are created,
we're ready to start modeling our gear blank.
We'll open up a new sketch on the front plane.
And we're going to create two concentric circles
based about the origin.
These circles will serve as our gears outer diameter
and bore.
The bore is simply the inner diameter or the through hole
that runs through the center of the gear.
So now we have to define our sketch.
So, start with the bore diameter.
And we are going to set this to be equal
and select the bore from the global variable dropdown
and hit the green check box to link the dimension
to the global variable.
Hit okay.
You know the variable is linked
when you see the red Sigma in front of the dimension.
We're going to create another dimension
for the larger circle.
This will be our outer diameter.
Our outer diameter equation is the sum
of the number of teeth plus two times the module.
So, are we going to set this to be equal to open parentheses
and then select number of teeth plus two times,
be sure to put spaces between all of your characters
cause it allows you to continue to pick
from the dropdown menu.
So we want our module.
And hit the green check box again.
And you should have a value of 38 millimeters
for your outer diameter.
Okay.
We're going to exit the sketch
and we will do a simple extrude boss base.
For the direction we're going to set it to be mid-plane.
I like to do this because it centers the front, top
and right planes about the center of your part.
Which just makes modeling a lot easier to do in my opinion.
And we will keep the width set to 10 millimeters.
This will be the width of our gear.
And hit okay.
Now that we've made our gear blank,
we're ready to start creating our gear tooth geometry.