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          Blender Tutorials: 608 Bearing - part 4

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Part 4 Constructing the Bearing Cage

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.
Select Balls

Num-Pad / Local View
Deselect all vertices A then Link Select the vertices of the top Ball, you do this by holding the mouse cursor close to a vertex on the top ball and pressing L.
We need to snap the 3d Cursor to the centre of this ball. Press Shift-S and choose Cursor to Selection.

Limit selection to Visible 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.

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.
Select Verts

Seperat Part 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.
Half Sphere
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.

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. 
Scale Verts
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

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 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
Extrude along Normals

Snd Vertices misaligned 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 
Scale Y axis to cursor
"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)

We 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.

For the knife to work from this vertex we now need to create a face as the knife only snaps to vertices that belong to a face.

Knife Cut

Knife Cut

Shift-RMB select the two top edge vertices closest to the new vertex and press F to add a new face.

Create a similar face on the other side of the bearing cage.

Go into wire frame mode Z and select all A and press K for knife. The mouse icon will change to a knife.

Move the knife close to the reference vertex and holding down Z
when a green snap point shows over the vertex click and release with the LMB, the cut line will be snapped to the reference Vertex.

Cut Line
Drag the line to the right and when you are near to the reference vertex on the other side of the bearing cage the snap point will apear on that vertex.  Click LMB to set the cut line and then Enter to cut new vertices.

Cut Line You can now select and delete the two reference verticies, which will also remove the unnecessary faces.
New vertices

Select 6 edges

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. 
Edge Select
Select Shift-RMB over the 6 edges indicated and delete X selecting Edges from the delete menu. Repeat this on the other end.
Select edge loop 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.

Spin Dup Cage As the cage has been created from the 608-Balls Object, its object centre is on the bearings centre axis. Tab into Object Mode and snap Shift-S the cursor to Selection this will centre the cursor on the bearing axis. Tab back into Edit Mode and select all vertices A.
On the Tool Shelf click Spin set Angle: to 360, Steps: to 7 and select Dupli. To remove the doubled vertices on the top cage, select all vertices A and remove doubles W
Vertex Select

Select Loop
Click back into vertex select mode.

We now have 7 cage profiles that need to be joined together.

It is easier to work on the bridging section at the bottom of the cage as it will be horizontal and aligned to the world axis.
Zoom in on the bottom two cage profiles and select the loop of vertices around one of the open ends Alt-RMB

Extrude Edge loop Shift-Alt-RMB select the loop of vertices on the horizontally opposing cage.

We now need to bridge the gap between the two selected loops of verticies. Fortumately Blender provides a tool to carry out this function.

Press W for the Specials menu and choose "Bridge Two Edge Loops". The two cages will be joined together by a loop of new faces.
Local View

2 shells joined 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.
Delete loos shells
To create the vertices that will eventually form  the joining tab, we need to cut two edge loops around the bridge section. To do that position the mouse over the bridge and press Ctrl-R to cut an edge loop, then press 2 from the keyboard numbers (not NumPad) which will draw two magenta edge loops. Press enter to cut the edge loops.

Two Edge Loops
Two new edge loops will be formed on the bridging section, but not in the position we require them in.

To reposition the vertices we will use Edge Slide to slide the loops of vertices towards the cage sphere profiles. Alt-RMB select one loop and turn on "Edge Length" in the Mesh Display panel.  
Edge Slide

Edge Slide
Press Ctrl-E to open the Edge Specials menu and choose "Edge Slide". Slide the loop of vertices until the bottom vertices are 0.3mm from the cage sphere profile as shown above. Whilst moving the loop you can press Shift to give finer control of the movement.

2 new edge loops 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 Dupli the selected vertices. Angle: 360, Steps:7.

Select all and remove doubles. 

Edge slide apart

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 Object Data panel change the Objects name from "608-Balls.001" to "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-S and save your work.

Ensure the 3D Cursor is still on the object center.

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 do
es 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) then Y for the axis. Press Enter to accept the Mirror operation.
Spin Dup 1st cage

The copy will flip over to be a mirror image of "608-CageA" with the name "608-CageA.001".

In the In the Object Data panel rename this object "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 which is on the top right of the default layout.

Mirrored Bearing Cage

By clicking on the objects name in the outliner, the object will become selected in the 3D view.

Clicking on the arrow will lock the object so it can't be accidentally edited.

The 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. 
Outliner Tree

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.

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.

Blender Window

In Edit Mode zoom in on one of the cage spheres and set the selection to Edge Select. Edge Select

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.

Check you have four continuous loops selected. This check may be easier in wire mode Z.

To bevel press Ctrl-B then press 0.05 for the bevel size. Press Enter to accept the Bevel.
Select Edges

Applied Chamfer Press Bevel and after a few seconds a chamfer will be created on the selected edges.

To get the correct smooth appearance on our cage we will add an Edge Split modifier. In vertex Select, select all vertices A and in the Tool Shelf Shading tools press Smooth.

In the Modifiers panel press Add Modifier, From the pop up menu choose Edge Split.

In the Edge Split modifier  "Sharp Edges" and "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. 
Mesh Modifiers

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

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.
608-CageA finished


<< 608 Part 3 Ball Bearings Tutorials 608 Part 5 The Cage Clasp >>

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