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          Blender Tutorials: 608 Bearing - part 4

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Part 4 Constructing the Bearing Cage

Video tutorials of this pages contents

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
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.
Select Verts

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.

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 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
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.

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.
Knife Cut

Cut Line 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.
New vertices

Select 6 edges 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. 
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->Selection to centre the cursor on the bearing axis. Tab back into Edit Mode and select all vertices A.
In the Mesh Tools panel set Degr: 360 and Step:7 and Spin Dup the vertices. Select all vertices A and remove doubles W
Select Loop Click back into vertex select mode.
Vertex Select

We now have 7 cage profiles that need to be joined together. Zoom in on the top profile and select the loop of vertices around one of the open ends Alt-RMB

Extrude Edge loop
In front view extrude the selection E and accept Only Edges from the sub menu. Drag the extruded vertices towards the next cage profile.

We 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.
Local View

Merge Vertices
Repeat this for all the vertices around the loops to be joined.

Merge Loop

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, 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.

Delete Vertices of one shell 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 Tools 1 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 top 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 Dup the selected vertices. Degr: 360, Step: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 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 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)
Spin Dup 1st cage

Mirror Axis Sub Menu 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.
View Border Arrows
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
Mirrored Bearing Cage

Split Screen 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. Split Line
New 3D Window
LMB click and a new 3D view will be created.

Outliner 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.

Outliner Tree
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. 

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.
Bevel Cener

Blender Screen 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.

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

Select Edges 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.
Bevel SettingsIn the Bevel Centre Shift-LMB over the thickness figure and change it to 0.05. This will give a 0.05mm chamfer.

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).

Applied Chamfer 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.

In the Edge Split 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. 
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

The following are video tutorials of some of the details above

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

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