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Back To Tutorials
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Part 6 Modeling The Dust
Shield |
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The dust
shield will be formed in the same way as we made the bearing
inner and
outer race. We will create a section through the dust shield and spin
this around the bearing centre to form the 3D component.
In the Outliner set the
608-Race to visible and hide all the other parts. In
Object Mode snap the cursor to the 608-Race object to set the cursor in
the centre of the bearing.
We will start this object
with a plane, so press the Space
Bar to open the Tools menu and
Add>Mesh>Plane. The plane opens in Edit Mode.
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Drag
the four vertices of
the plane and position them in the retaining grove of the outer race.
Select the bottom two vertices and delete them X as we will start
the
dust shield using only the top two vertices. |
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Grab G the end vertex and
move it along the Y axis 1.75mm
so the top edge measures
0.25mm, the thickness of the dust shield.
Extrude E
(Only Vertices) the two end vertices in the Z axis -0.75.
Grab G the
inside bottom vertex and move it in the Z
axis
a further -0.144mm
to form an angle between the two vertices of 60 degrees from
the
vertical. |
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Set
the cursor on the
inside lower vertex and then extrude this -1.5mm in the Y axis.
Rotate R this
edge -30
degrees from the cursor.
Repeat
this for the outer
edge. |
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The dust
shield
offsets 0.85mm so extrude two reference vertices from the top corner.
-0.6 then -0.25 in the Y axis
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Extrude
a face from these vertices constrained to the Z axis and position the
new vertices between the dust shield edges. Extrude another face along
the
Z axis below the dust shield.
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We will use the reference
edges to accurately cut the angled dust shield edges to length.
Select
all vertices A
and open the knife menu K,
select Knife (Exact)
Click LMB
below the lower right reference vertex, press Ctrl and move the
knife towards the bottom left vertex the cut line will snap to the
vertex click LMB
to set the line then move to the vertex above Ctrl LMB this vertex
to snap the cut line, then press Enter to accept the cut. |
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Repeat
this on the outer
edge but start the cut line on the top left vertex and cut to the
vertex below.
We now have two new vertices setting the offset width of the dust
shield.
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We no longer need the
reference vertices or the end vertices of the dust shield edges.
Select these vertices and delete them X
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Select
the two end
vertices of the dust shield ready to extrude them. |
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Before we extrude them we
need to set the cursor on the top of the inner bearing race. Tab into Object mode
and select 608-Race. Tab
back into Edit Mode for this object. Select a vertex from the top of
the
inner race RMB
and snap the cursor to this, Shift-S
Cursor->Selection.
Tab
back into Object Mode, select the Plane object (dust shield) and Tab
back into Edit Mode for this object. |
Extrude
the two selected
vertices towards the inner race constrained in the Z-axis.
We will now scale them onto the inner race.
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With
the pivot point still set to 3D cursor press S for scale Z to constrain
the movement to the Z axis and 0
to scale the lines level to the cursor.
The vertices are now touching the inner race so we need to back them
off a little to provide some clearance. |
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Move
the vertices G
(grab) Z
constrain 0.02
for the clearance. The vertices will now be
clear of the inner race.
To complete the basic shape of the dust shield press F to put an edge
between the vertices. |
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We
now have the basic cross section of the dust shield positioned
accurately against the bearing race. As we no longer need to reference
the bearing race press Num-/
to go into local view for the dust shield.
The last thing to do to the cross section is add some fillet radii to
the offset corners.
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Adding
Fillets
I
will show two methods of accurately positioning the fillets, one using
trigonometry and one using reference geometry that has no need for a
calculator. For both methods you will need to know the angle between
the edges,
the fillet radius and have one edge aligned to a known axis.
Fillets
- Trigonometry Method |
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First
we need to know the angle between the edges we are going to fillet. If
you haven't been planning the construction of your model and placing
lines arbitrarily you can find the angle by forming a face from the
three vertices and using the edge angle button in the Mesh Tools 1
panel.
Another requirement is for one of the edges to align with a known axis. |
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work out the centre point of the fillet we simply construct a right
angle triangle with half angle A and the radius. The hypotenuse is the
distance to the centre point at an angle of half A |
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Therefore
Sin
1/2A = Radius/ Hypotenuse
Hypotenuse = Radius/ (Sin (A /2)) |
Once you have determined
the hypotenuse simply extrude E
this from the intersect along the known
axis and rotate R
it 1/2 angle A |
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Fillets
- Reference Geometry Method |
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Using
the knife tool K snap
a cut line Ctrl-LMB
between the two reference vertices parallel to the known axis line and
cut a new vertex on the centre point of the fillet. |
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From
the centre point extrude a vertex perpendicular to the edge on the
known axis at the length of the fillet radius. |
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Set
the cursor on the centre point and spin the vertex on the end of the
radius edge through an angle of
180 - Angle A |
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Delete
the reference vertices. |
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Re
make the edges between the fillet and surrounding vertices. |
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Getting
back to the dust
shield we will use the reference geometry method to position the
fillets with a small radius of 0.1mm and a large radius of 0.35mm. The
angle between the edges is 120 degrees. |
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From the intersect on the
inside of the angle extrude E
a vertex along the Z
axis 0.15mm,
then
rotate R
the vertex -60 degrees. |
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extrude a vertex -0.1 in the Y axis (distance of radius ) and
then extrude this above the 60 degree edge. |
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In
edge select mode press B
twice to bring up the selection painter reduce
the size of the selection circle MW
and select LMB
the
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edges between
the fillets. Delete X
these edges.
Repeat this procedure to produce the bottom fillet.
Back
in Vertex Select mode, select the
reference vertices along with those on the original angle intersects
and delete them. We are now left with the fillet's and top and bottom
edges of the dust shield. |
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Select a vertex either
end of a missing edge and press F
to insert a new edge.
Repeat
this for all the open sections. |
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We
are now left with a completed cross section through the dust shield
ready to spin into the 3D object, however as before the cursor is in
the wrong position.
Select all A
the vertices and Tab
into Object Mode. |
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Snap
the cursor onto the object centre. Shift-S
Cursor->Selection.
Tab
back into Edit Mode and go to front view NumPad-1.
In the Mesh Tools panel set Degr:360 and Step:64 press spin to form the
3D object.
Select all vertices A and remove Doubles W. |
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The
dust shield is now almost complete, but chamfers are required on the
corners.
In edge select mode loop
select the four edge loops indicated Shift-Alt-RMB. |
Using the Bevel Centre
script detailed in
Part
4, add a 0.05mm chamfer.
Finish the dust shield by adding an Edge Split modifier also detailed
in Part 4.
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A
Dust shield will also be required on the other side of the bearing.
Rather than repeating the modeling process we will duplicate this dust
shield and Mirror it across the bearing centre.
Tab
into Object Mode and go to the side view NumPad-3. Check the
cursor is still on the object centre.
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Press Shift-D
to duplicate the object then Esc
to leave the duplicate on top of the original.
Press Ctrl-M to open the
Mirror sub menu and select "X Local". |
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Both
Dust shields
have now been created so it is time to give them a meaningful name.
Select Plane in the outliner and then in the Links and Materials panel
change its name to OB:608-ShieldA. Repeat this for Plane.001 naming it
OB:608-ShieldB.
Press Ctrl-W
and save your work.
The final components for the bearing assembly are the circlips that
retain the dust shields in place. These are covered in the next section. |
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