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Back to Tutorials |
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Designing a casting. Part 2 Initial Layout |
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We now have all the components needed for the X-axis roughly
positioned. So it's time to put a little thought into what shape the casting
needs to be to accommodate the components. | |
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In front view the components are fairly spread out and could possibly
be moved closer to the centre to reduce the footprint of the X-axis. |
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side view its clear that some of the components will penetrate the
front mounting face of the casting. It will be necessary to
provide a recess behind the roller nut and top right hand bearing.
The size and location of the recesses will determine how close the other components can be to the centre of the casting. |
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The
first part of the casting to model is the recess behind the
Roller-nut. To make modelling easier you can hide the slide shaft and
lead screw by clicking the eye icon in the outliner. Select an adjuster
block and in Edit mode snap the cursor to the front face of one of the
adjuster blocks. Tab into Object mode and in front view add a plane. In
object mode move the plane central to the Roller nut and resize it so
it is larger than the nut. One side should be aligned with the back of
the axle flange.
Delete X Only Faces to remove the face from the plane. |
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Extrude the four edges Y 8mm. This will add depth to the recess.
In side view Grab the top back vertices and move them, Z -8 mm to give a 45 degree angle. Move the bottom vertices up 8mm. |
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In top view move the back side vertices in 1mm to add a withdrawal taper.
Finally add a face to form the back wall. |
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I
have repeated the process for the top Right-hand bearing. This time
making a little extra room for the axle and nut which also penetrate
the front plane of the casting.
With the two recesses modelled it's easy to see where the rest of the
components can |
be repositioned to make the casting more compact.
Theirs plenty of room to allow me to move the V-roller centres from
150mm to 110mm. It's also apparent the Adjuster blocks are larger than
they need to be so I will reduce their size. |
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Select one of the adjuster blocks and Tab
into edit mode. It's not possible to just scale everything to a smaller
size because this will also resize the centre hole, slots and flange
widths. So I need to resize it in stages.
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The square centre hub is 44mm
and I am going to reduce it to 36m. Box select the centre hub and
flange vertices directly above and below it. Scale this on the X-axis by 1.2222 (44 / 36).
Now box select the vertices of the right hand flange and move G these on the X-axis -4mm (1/2 the 8mm difference). |
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Repeat this with the left-hand flange. Moving it 4mm on the X-axis.
Box select the vertices of the centre boss and the flange vertices
directly to the left and right of it and again scale this 1.2222 but on
the Z-axis. Then grab and move the top and bottom flanges 4mm.
You should now have a square adjuster block. |
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In
scaling the adjuster on the Z-axis we have also just scaled the slotted
bolt holes. These need to be returned to their original size.
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We can
do this by scaling the vertices of the slots by the inverse of the
original scale (1 / 1.2222 = 0.81818).
Select the vertices of the first slot and Scale it Z 0.81818 Repeat this on the other three slots. Finally scale the centre hole on the X and Z-axis by the same amount to return the hole to the correct diameter. (Scale Shift-Y 0.81818) |
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With the
adjuster blocks reduced in size I have been able to further reduce the
V-roller centres, which are now 100mm apart. I have also moved the
bottom V-rollers in 6mm so the edge of the adjuster blocks are level
with the outside of the top V-roller's.
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To form the pockets in the casting where the adjuster blocks sit we can copy both adjuster blocks Shift-D then press Escape to
leave them in position. We can then cut and adapt the copied adjuster
blocks mesh to form the adjuster locations in the casting.
With the copied blocks still selected go into local view NumPad /.
In side view select the front face of the adjusters. Snap the cursor to
the selection so it's on the same plane as the front face, then delete
the vertices.
Because of the chamfer the front loop of vertices is no longer aligned
on to the front face of the casting.
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cursor select mode Scale the vertices on the Y axis to 0. This will bring the edge back into alignment. |
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Select and delete the vertices of the central hole, to leave us with a recess the same shape as the adjuster.
If it were left like this there wouldn't be any room for the adjuster to
slide on the Z-axis. So we need to mover the top and bottom flange to
allow the adjuster to move. |
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| Select the vertices of the top flange and Grab them moving them on the Z-axis 4.5mm. Move the bottom flange -4.5mm. This will give us the room for the adjuster block to move up and down. |
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The adjusters will be secured with a 4mm bolt, so the casting needs a 4mm-tapped hole centrally to the slot.
It's not practical to model the thread so it will simply be represented by a hole at the tapping drill size, which is 3.3mm.
Select the four vertices from the straight edges of the slot and snap
the cursor to their centre. Add a circle with 16 vertices and a radius
of 1.65mm. |
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Delete the vertices of the slot then rebuild the faces around the hole.
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Using Blenders snap tools, copy and paste the hole and surrounding faces to the other locations.
At this stage it will also be good to delete unnecessary vertices and rebuild the faces as larger quads.
Blenders skin Face/Edge Loop feature will be useful for this.
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Once one adjuster recess is complete, copy it and move it 88mm on the X-axis so it sits behind the other adjuster.
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To position the fixed axle holes, RMB select a fixed axle and go into Local View NumPad /. Select Shift-Alt-RMB the loop of vertices at the back of the
fillet and snap the cursor to the centre of them, Shift-S Cursor>Selection. This gives us the
location point for the adjuster. Go into Object Mode and in front view Insert a
mesh circle, SpaceBar
Add>Mesh>Circle, in the popup menu set Vertices: 32 and Radius: 3. Repeat this for the other axle.
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Select the axle location circles, the pockets behind the roller-nut and
bearing and the adjuster recesses and combine them into one mesh, Ctrl-J.
These are the first features of the casting.
In order to locate the roller-nut and bearings, three adjuster brackets
are required. I will construct these in Part-3. This will then
allow me to add their mounting locations to the casting.
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