>> This is a short video with hints
for doing homework number three and lab number three.
Let's start with homework number three.
Okay, first part of it is doing a linear sweep.
This problem here, we are given a series
of three dimensional profiles that are constructed on the X,
Y. So for this one here, we're supposed to do a linear sweep,
okay, in the positive Z axis two units.
So what we need to do is move this profile here,
make a copy of it two units forward in positive Z direction
and then connect them with lines.
The original profile and then your profile created.
Now, how does that work?
You're supposed to do that on paper and pencil.
But how does that work on auto tab?
Use that illustration.
I'm going to do it for the second one, okay?
For the second one here, it's the original profile.
Let's change our point of view so that we see X,
Y and Z. I'm going to be working on the one on the left.
So I'm going to do what's called an extrude.
This whole profile here, I'm going to extrude it
in the positive Z direction to give it depth.
And that becomes a solid.
So that's one we are creating 3D objects from 2D objects, okay?
That's called linear sweep.
And you're going to do it right
on the paper that's provided right on the profile.
Now, the second part, we do what's called a circular sweep.
So this profile here of B,
we go to the Y axis becomes number five.
So it's multiple choice or matching.
So if you look at A and again the one above the Y axis,
it becomes number eight.
That's a circular sweep.
Now, let me illustrate circular sweep again, 4.3,
focusing on this profile, the second profile B. I'm going
to illustrate how that works.
When you rotate it about the Y axis at 360 degrees.
So going back to AutoCAD,
looking at the same profile here, this time on the right,
okay, I'm going to revolve this, rotate this, do a circular sweep
of this profile about this line to this end point
and this end point and at an angle of 360 degrees.
So this is a resulting solid, it's a solid revolution
by revolving the original profile here
about the vertical axis of the Y. So what you need
to do is catch the resulting circular sweep.
Now, the last part of this homework is you're given three
solids, the cylinder and two boxes.
You're supposed to position the boxes,
relative to the cylinder shown here,
and then to this Boolean operation,
I'll subtract A minus B minus C,
and then the resulting profile, solid sketched in the isometric space.
Illustrate it in AutoCAD again.
Here are the three cylinder horizontal box
in the vertical box.
The first thing I do is move the horizontal box
from its current location so that the midpoint
on that edge is going to then over the center
of a circular box for the cylinder.
And then repeat the move command this time
for the skinny vertical box by taking the midpoint again
to the same location here in the center of the circle on top.
And then I'm going to do the boolean operation
of subtract, okay?
Object to subtract from over the cylinder, press enter,
objects to subtract are the two boxes and then press enter.
This is what is the resulting 3D object.
And you're going to sketch that 3D object
in this isometric space that's provided.
Finally, the last part of this tutorial is related
to lab three.
Lab three, you're going to use concepts of internally tangent
and externally tangent circles.
These circles are externally tangent, such as this one here
in the middle and this one on the right.
They are tangent to each other.
And the smaller one is outside.
Here is another pair of externally tangent.
The biggest one is 3.5 and externally tangent.
Internally tangent example is the 3.5, the big one
and the tiny one already is 1.5 because the small one is inside.
Now, the relationship between externally tangent is the
difference between the centers, okay, 5, is equal to the sum
of the radii, 3 and 2, when they are externally tangent.
Another illustration is let's see the pair,
externally tangent is two biggest ones, okay?
If we look at the distance between the centers of the two,
center of the big one and center three, the distance
between them is 6.5 because the sum of the radii is 3.5 less 3.
On the other hand, for the externally tangent, okay,
the distance between the two,
the center for the two is two units
because it's the difference between the radius
of the bigger one, 3.5, minus the smaller one.