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Back to Tutorials
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Part 4 Constructing the Bearing
Cage
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| Video tutorials of this pages contents | |
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When
we inserted the UVsphere that formed the ball bearings it was important
to ensure that one of the poles pointed to the centre. By doing this it
has left us with the rings of the ball running perpendicular to the to
the bearing center axis and this allows us to extract the geometry
from the surface of the UVsphere to form the inner profile of the
bearing
cage. This will become as little clearer as we work through this part
of
the tutorial.
In
front view select the balls, as the bearing race will get in the way of
our view select local view NumPad
/. This will remove everything from view except the
selected objects.
With
only the balls in view, zoom in and pan on to the top ball, SW (scroll wheel) to
zoom, Shift MMB
to pan.
Tab into Edit Mode
and go into solid view Z. |
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On
the view header select the Limit selection to visible button, so you
only select vertices from one side of the sphere. |
Without this being
checked you would also select the unseen vertices from the back of the
sphere.
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Box
select B 8
rings of vertices starting from the centre ring and moving towards the
bottom of the sphere.
We
will copy these vertices and turn them into a new object, they will
then form the inner part of the bearing cage. |
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Press Shift
D to copy the vertices, then press Esc so
they aren't moved from their original position. A new set of vertices
has been created on top of the sphere. With these still selected press P
(part) to separate them from the 608-Balls object. A new object has now
been created and removed from the current Edit Mode selection. |
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Tab into Object mode
and though not visible the new cage object is on top of the top
UVsphere. RMB
click over the cage and its outline will be highlighted. Tab back into Edit
Mode. |
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Currently
the vertices of
the cage are sitting on the surface of the
ball which would stop the bearing from turning, so we need to add some
clearance. To achieve this we will scale the cage from the centre of
the top ball bearing.
First
we need to set the cursor at the centre of the top
ball. Tab
into Object Mode and select the 608-Balls Object. Tab into
Edit Mode and de-select all A
move the mouse close to a vertex on the top ball and press L
(link select) this will select all the vertices directly linked by an
edge to the vertex you are closest to. All the vertices of the top ball
will now be selected. Shift-S
and snap Cursor->Selection, this will centre the cursor on the
top ball.
Tab back into Object
Mode and select the Cage then Tab
back into Edit
mode.
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| Make sure the Pivot Point is set to 3D
Cursor and scale S
the cage 1.02 This
will give you a clearance of 0.0395 between the ball and the
cage. ((Diameter * 1.02) - Diameter) / 2 |
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We
have now got the inside profile of the cage but we need to add
thickness to it. We could simply Extrude a new set of vertices and then
scale them from the centre however we would need to work out a scale
factor. Instead Blender has the ability to scale all faces in the
direction of the face normals (see Blender Wiki for explanation of
Normals). As we are scaling individual vertices then we only need to
use the thickness as the scale factor.
With
all the vertices selected extrude E
select “Region” from the sub menu and then press Esc
so the new vertices don't change position. Press Alt-S to scale along
normals and -0.3
for the thickness then press Enter.
The cage is now 0.3mm thick |
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As
we have created the thickness of the cage by scaling in
the direction of the faces,
the new end vertices are
no longer on the centreline of the bearing. With the cursor still on
the centre of the top ball and Pivot set to 3D cursor, select the new
end vertices (you will
need to deselect the |
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| "Limit selection to visible"
button or go into wire view Z)
Shift-RMB
and scale S
in the Y
axis to 0. (It
may be easier to select all the end vertices of the cage as those that
are already on the centreline won't move. Box Select vertices
within the area outlined
above then with pivot in 3D Cursor, Scale
Y-axis
to 0) |
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now have the cage form that surrounds the bearing but if we Spin Dup
this we will still be missing the section that bridges between this
ball surround. Therefore before we Spin Dup this section we need to
locate vertices so the bridging section when formed is 0.3mm thick.
In
top view
select the outer most vertex and extrude it -0.3 in the Y axis. This
vertex will be the reference point to cut a new row of vertices.
Select
all A and
press K
(knife) a sub menu will open select Knife (Exact). The mouse icon will
change to a knife. Move the knife close to the reference vertex and
holding down Ctrl
click with the LMB
the cut line will be snapped to the reference Vertex. |  |
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Drag
the line to the right and click MMB
this will constrain the cut to a line running horizontally along the
view, which is the X axis. With the line passing all the edges of the
left side of the cage click LMB
to set the line and then Enter
to cut new vertices. |
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Repeat
the cut on the other end of the cage,
then delete X
the reference vertex.
We now have a row of vertices running parallel with the back face of
the cage at 0.3mm. We will need to delete the faces
and edges
between this new row and the back edge. To make selection easier go
into Edge Select.
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Shift-RMB
over the 6 edges indicated and delete X selecting Edges
from the delete menu. Repeat this on the other end. |
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The
cage profile should now have a row of faces
missing on either end. When extruded and joined to the next cage
profile, this will allow us to have a continuous shell without any
faces or edges inside the model. |
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In
front view extrude the selection E
and accept Only Edges from the
sub menu. Drag the extruded vertices towards the next cage profile.
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now need to merge the extruded vertices onto the next cage
profile. To do
this select one vertex on the extruded edge (1) then Shift select the
corresponding vertex on the next cage profile (2). Press Alt-M to open
the Merge sub menu and select "At Last". This will join the vertices
at the position of the last selected vertex. |
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Repeat
this for all the vertices around the loops to be joined.
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We now have two cage shells joined together
with a connecting bridge all with a thickness of 0.3mm.
Soon we will mirror this cage to form the cage on the other side. But
before this a
little more geometry is needed, as the two half cages are joined
together with a folded tab over the outer circumference of the cage. |
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To
create
the vertices that will eventually form the joining tab,
select all A
and
cut through the bridging section K
but this time accept Knife
(Multicut) from the Cut Menu. A new sub menu will open allowing you
to choose the number of cuts. Accept the default 2.
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With
the two edge loops slid to a position 0.3mm from the cage spheres
select the vertices of the bridge section. (The two edge slide loops
and the two loops connecting the bridge to the sphere. |
Ensure the cursor is
still on the bearing centre axis and Spin Dup the selected vertices.
Degr: 360, Step:7.
Select
all and remove doubles.
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You
have now made the basic construction for one half of the cage.
We
will chamfer the edges of this but first we need to copy and mirror
this object to make the other half of the cage.
In the Links and Materials panel change the Objects name from
OB:608-Balls.001 to OB:608-CageA. The previous name was automatically
assigned by Blender as copy 001 of the 608-Balls object, from which we
copied
the cage geometry.
If you have not been doing so at frequent intervals press Ctrl-W and save your
work.
In Object Mode go to the side view NumPad-3
and copy the cage Shift-D
then press Esc
so the position of the copy does not move.
We now need to Mirror this copy on the Y axis. Ensure the cursor is on
the Object Centre (centre of the bearing) and press Ctrl-M (Mirror) |
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This
will bring up the Mirror Axis sub menu choose "Y Local".
The copy will flip over to be a mirror image of OB:608-CageA with the
name OB:608-CageA.001. |
In
the Links and Materials panel rename this object OB:608-CageB.
Our model
now consists of four objects. To make selection easier
blender has the ability to show an object layout in the form of
a tree structure. This is seen in the Outliner window.
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To
enable this we first need to make room on our screen for a new window.
Move the mouse over the join between the 3D view and Buttons Windows.
The mouse pointer will change to a double arrow |
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RMB click whilst
the arrows are showing and a sub-menu will appear, LMB click on Split
Area. A split line will follow the mouse pointer. Move the mouse over
the 3D view. |
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LMB click and a new
3D view will be created.
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Click
on the Window type button in the lower left corner of the new window, a
Window type menu will appear choose Outliner.
The view will now show a list of all the objects that are in our scene
(assembly and 3D space). Together with the default Lamp and Camera.
It may be necessary to increase the width of the outliner window to see
all the options. To do this move the mouse pointer over the
join
between the 3D view and outliner, the pointer will change to a double
arrow. Hold down the LMB
and drag, the size of windows will change according to the mouse
position.
By clicking on the objects name in the outliner, the object will become
selected in the 3D view.
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Clicking
on the arrow  will lock the object
so it can't be accidentally edited.
The square camera icon  stops
the object being rendered to a bitmap image but still allows you to see
it in the scene.
Clicking on the eye symbol  will
show or hide the object in the 3D view. |
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Now
we have both sides to the bearing cage however there is still one
operation that
needs to be performed on OB:608-CageA. No mechanical parts have a
perfectly square edge especially pressed parts like the bearing cage.
So
we need to add a chamfer to the outer edges of the object.
This
process is greatly simplified by using one of the python scripts,
so we need to open a scripts window. As above with the Outliner, split
the 3D view but this time on the right hand side of the view. From the
window type menu choose scripts window. In the scripts window LMB click on Scripts
go to mesh and choose Bevel Centre. This will be used to add a chamfer
to the chosen edges. |
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In
the outliner window click on 608-CageA to select it and then click on
the eye icon for the other objects to remove them from view.
Your screen will become quite cluttered and with the need to open more
and larger windows the 3D view will become uncomfortably small,
especially if you are using a small monitor. To make selecting and
modeling easier you can force any of the windows to full screen by
pressing Ctrl-Down Arrow
with the mouse pointer over the
window, giving a much better work area. pressing Ctrl-Down Arrow
again will return the screen to the normal layout.
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Edit Mode zoom in on one of the cage spheres and set the selection
to Edge Select. |
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I'ts
now a matter of selecting all the edges on the outer and inner
circumference.
Shift-Alt-RMB
select the edges
indicated and work your way all around the circumference of the
cage. |
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you have four continuous loops selected. This check may be easier
in
wire mode Z. |
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 In
the Bevel Centre Shift-LMB
over the
thickness figure and change it to 0.05. This will give a 0.05mm chamfer.
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| Blender 2.46 Update
Blenders internal Bevel tools have been improved so you no longer need to use the "Bevel Center" script for chamfers.
To create the same bevel as detailed simply select the edges you wish to bevel press W for the Specials menu and select Bevel, Type the bevel size you require (in this case 0.05mm) and Enter. The bevel will be created.
The Bevel Center script is still useful as the Blender internal bevel does not yet support recursive (bevelles with a radius). |
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Press
Bevel and after a few seconds a chamfer will be created on the selected
edges.
To
get a smooth appearance
on our cage we will add an Edge Split modifier. In vertex Select,
select all vertices A
and in the Mesh Tools panel press Set Smooth.
In
the Modifiers panel press
Add
Modifier, From the pop up menu choose Edge Split.
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modifier "From Marked As Sharp" and "From
Edge Angle" will already be selected. Leave Split Angle:30.
Which
will
smooth the join between any faces with an angle of 30 degrees or
less. |
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If black patches appear
on the surface this is because the computer
doesn't know what side of the face is outside. To correct this press Ctrl-N and
recalculate normals outside |
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OB:608-CageA
is now
complete.
Pres Ctrl-W
and save your work.
In part 5 we will add the clasp that joins the two half cages to
OB:608-CageB. |
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The following
are video tutorials of some of the details above |
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