Chapter 20- Springs, Screws and Gears

Chapter 20- Springs, Screws and Gears
So far, we see that Blender has many features that are found in
almost all 3D computer programs like the ability to extrude along
paths, subtract and add meshes through Boolean expressions and
now we will examine revolving-type, or spinning commands. The
commands used for these effects are found in the Tool Shelf and
are visible when in Edit Mode. The Spin and Screw commands can
be used to revolve around a center point with duplicate objects or
smooth spinning. You can also provide an offset that will create a
spiral. The process to get them to work can be confusing to
beginners so we'll create some basic shapes.
Creating Screws and Gears
There are actually mesh add-on tools that can create both of these items easily that will
be discussed later in the chapter, but for now, we will look at the traditional way to
create these items.
Screws and Springs:
In order to make these items, you need a closed shape for the profile (ex. circle or
triangle) and a 2-vertex line that controls the spacing from one coil to the next. We'll
make a screw form for our first example. Start by
adding a Plane. In Edit mode, select the 2 right side
verticies and scale them down to make a triangle
form that will represent the triangle thread. Move
the 3D cursor to the left side and place it where you
want the center of the screw to be.
Now add another plane (while still in edit mode),
delete the 2 right side verticies so that all you have is
a line, and place those 2 verticies on the 3D cursor.
These 2 verticies control the distance between the
coils and must be part of the 1st mesh. If they are not
joined together, use “Ctrl-J” to join them. My
example has the line the same size as the edge of
the triangle. This means that the threads created will be tight together. If you want
space between the threads, make the line longer. I place these 2 point on the 3D
cursor so it is easier to delete them later. Stay in Edit mode.
Now, use the “A” key to
select All verticies. The line
and triangle verticies should
all be selected. Make sure
you are in a principle view
since the spinning will occur
related to your view. Select
the Screw command.
Chapter 20- Springs, Screws and Gears
When you select the Screw
command, additional options
will display below the Tool Shelf.
Steps will control the quality of
the circular curve (I used 32).
Turns is the number of coils.
Center and Axis will do some
fine-tuning for you.
By spinning the mesh, you will be able to select the string of
verticies created from the line down the center.
In order to make a spring, you do the exact same thing as the screw, except you use a
circle instead of a plane. I will create 2 examples using a short line for close coils and a
longer line for wider coils.
Chapter 20- Springs, Screws and Gears
RoboDude Asks: How could I animate a spring stretching and compressing?
Remember how we made shape keys? Scale the shape along the axis and use
the slider to animate it.
Since a gear uses a 3D shape for the tooth and not just a 2D
profile like screws and springs, we need to use the Spin
command for that and duplicate the object as it is revolved. To
start, add a cube, switch to a front view and shape the one
edge to look like a wedge. I selected the 4 right edge verticies
and hit “S” to scale and “Z” to scale on the Z axis only. This is a
pretty simple gear tooth, but good for discussion.
Now move the 3D Cursor to
a location where you would
like the center to be. (still in
the front view). Enter Edit
Mode and select all verticies.
In the Tool Shelf, select the
“Spin” command. You will
need to adjust:
Steps to match the number
of teeth.
Degrees to 360 (full circle).
Dupli may need to be
verticies rather than spin
RoboDude Says: After spinning an object, you will probably have a double set of
verticies over the original tooth. Select all verticies and use the “Remove Doubles”
command in the Tool Shelf.
To finish off the gear, add a cylinder to the center and
shape/scale it to fit the teeth. You could also use
Boolean modifiers to cut holes for more detail. Join the
meshes together when finished.
Chapter 20- Springs, Screws and Gears
Creating Revolved Shapes
If you wanted to make a revolved shape, like a goblet or an alien
flying saucer, you could start with a circle and extrude it to make the
shape, but you could also use the Spin command.
For this example, I started with a plane, deleted one vertex, and
shaped/extruded the mesh into the profile of a goblet. Make sure the
3D Cursor is somewhere on the center axis line of the mesh.
Switch to a front view (or whichever
view you need) so you are looking
down at the shape and displays as a
line. Spinning is related to the view
you are working with.
Just like we did for the gear,
make sure all verticies are
selected and hit the “Spin”
command. You will need to
change the “Steps” (I used
“Degrees” to 360
for a full circle.
You will also want
To the left is a profile extruded in the top
view. The examples show spinning that
shape in a front view and a side view.
The active view at the time does make a
Don't forget- there are Modifiers listed that can do some of these features, only a bit
differently. You can actually specify an object for an axis and a few other things. Feel
free to experiment with them now that you have a better understanding of how to do
Chapter 20- Springs, Screws and Gears
Blender Add-On Meshes
Using the above techniques have always been in Blender and can work well for making
mechanical parts like screws, bolts and gears, but with version 2.5, there are now easier
ways to do these things. For the past several releases, there has been a script included
with Blender called Bolt Factory. It worked great for making bolts and nuts, but many
users didn't know it existed. Now, you can have that feature (and others) appear in the
“Shift-A” add menu by enabling the “Add-Ons” in the User Preferences menu. This has
been discussed earlier in the book, but here are the details again.
Go to the “File” pull-down menu and select “User Preferences”. In there, you will see a
tab called “Add-Ons”. There are a lot of nice features you may want to use in there
and by checking the box, the script will be enabled. For now, we are checking “Add
Mesh- Bolt Factory” and “Add Mesh-Gears”. If you want these enabled at all times,
save the defaults. There are
also many other mesh types
that could be useful in the
Add-Ons. These features are
pretty simple and easy to
figure out, but here are the
Bolt Factory:
When you hit “Shift-A” now, you will
see the 2 new options in the mesh
menu. By selecting “Bolt”, you will see
a list of options in the Tool Shelf area.
You can select bolt or nut, a preset
metric size, head shape and type,
lengths, etc. Almost everything you
need for quick hardware.
There are 2 different types of
gears you can add. A worm
gear and a gear (spur gear).
You have many setting options
that can be changed with
terminology related to real
gear development.
Gear Design Practice Exercise
Create a worm gear and a spur gear to mesh with each other using the information
discussed in this chapter. You can use the “Spin” and “Screw” Tool Shelf commands or
use the Gears Add-On in the User Preferences. Either method, try to keep the gear
teeth equal on each part. Try using the copy command for the basic tooth shape. Add
materials, textures and appropriate lighting. Make a 200 frame animation of the gears
turning. Try to make them mesh perfectly! Remember the Linear Extrapolation options
available in the Graph Editor Window. All you need to do is create a small section of the
animation and let the computer do the rest! If you need a refresher, review the
animation chapter and page 9-9 for animating the light in the lighthouse.
** Call the instructor when finished**
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