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          Blender Tutorials: Designing a Casting - part 1

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Designing a casting. Part 1 Positioning the components

By now you should be fairly familiar with Blenders modelling capabilities. The 608 Bearing and V-roller tutorials have covered most of the commonly used tools and techniques, so this won’t be so much of a tutorial as a discussion on the steps needed to use Blender as a tool to help you design a casting. As the next stage of my CNC router upgrade is to redesign the X-axis slides I will use this as the motive for designing the casting. We will again reuse the bearing and V-roller as the building blocks for the casting layout.

There are many casting techniques that could be used for this component such as sand casting, die-casting and centrifugal casting, but because of my limited workshop facilities and the availability of a pottery kiln, I have chosen to use the investment casting technique. This is where a wax model of the part is fabricated then dipped into a refractory slurry which is dried, the wax is melted out leaving the refractory casing which when fired becomes the mould for the molten aluminium. The mould is then broken away from the aluminium when it has cooled.

The benefit of this method is you can produce an accurate wax model without worrying too much about withdrawal tapers or undercuts, If you can make the component in wax you should be able to produce an investment mould from it. I will go into a little more detail about the mould making and casting process in the foundry section. Here I will concentrate on using Blenders modelling capabilities to design the casting.

If you haven’t already got blender running this is the time to start it up? Delete the default cube X and then append into the scene Shift F1 the V-Roller, bearings, shaft, nut and washer assembly created in the V-Roller tutorial. They will be placed into the scene rotated so the roller will run along the X-axis. Go into side view NumPad 3 as we need to add a shaft for the V-Roller to run along. To make sure the shaft is centred to the V-Roller, select the V-roller and in the Edit Buttons click “Centre New” this will ensure the object centre is on the centre of the V-Roller. We can now snap the cursor to the V-Rollers object centre Shift-S Cursor>Selection. V-Roller assembly

Add a cylinder to represent the shaft SpaceBar Add>Mesh>cylinder and in the popup menu set Vertices: 32, Radius: 9, Depth: 100. In its current position the shaft penetrates through the V-Roller so we need to move it down so that the shaft sits below the ‘V’.  Shaft centred on V-Roller

Tab into Object Mode then Grab the shaft and move it on the Z-axis until it sits just below the V-Roller. Zoom in fully and repeat this if necessary to get the closest possible alignment.

You can also zoom into a selection box by pressing Shift-B and dragging a selection box over the zoom area you require.

In front view NumPad 1, Tab into Edit mode and Box select the right-hand vertices. Move these vertices G along the X-axis 300mm. This will make the shaft 400mm long. Tab back into Object Mode.
Align Shaft

It's possible to have the V-Roller rigidly aligned to the X-axis using just 3 rollers, as I am going to reuse this set-up on other areas of the machine I am going to use 4 rollers. In front view NumPad 1, Box select the V-Roller assembly and copy it Shift D. Move it along the X-axis 150mm. Now Box select both V-Roller assemblies and copy them Shift-D, moving the copies on the Z-axis until the ‘V’ is below the shaft. In side view NumPad 3 Zoom in close to position them as accurately as possible V-Rollers

Its not feasible in a home workshop to make components to micron accuracy so some form of adjustment will be necessary to position the V-Rollers tight to the shaft. I am going to fix the top two rollers into the main casting, but allow the bottom rollers to be adjusted on the Z-axis. For this I will use a simple rebated block with elongated bolt holes. This can simply be located within a rebate in the main casting. Axle alignment

The Adjuster Block

To make the adjustable block, RMB select the bottom right hand V-Roller 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. Position Cursor

Whilst still in Edit Mode add a Plane and Scale it by a factor of 22 to give a 44mm square. Delete the face from the plane X “Only Faces” then subdivide the edges 7 times. W “Subdivide Multi” and set 7 in the popup menu. This will give our outer square the same number of vertices as the inner circle. Add faces between the inner circle and outer square by pressing F and selecting "Skin Faces/Edge Loops". Select all and Extrude "Region" along the Y-axis 10mm, to add thickness to the component. Face of Adguster

In order for the adjuster block to be able to be positioned in the casting it needs some side flanges that will also incorporate the elongated bolt holes. In side view NumPad 3 cut a loop of vertices K "Midpoint". Grab the new loop of vertices and move them on the Y-axis -2mm, this will give us a 3mm face to form the flange from.

Select the flange face's, one side at a time and extrude them 10mm. The top and bottom flange will shield the components of the slide from dust produced by the router.
Cut Vert's for Flange

Extrude Flange Delete the two corner faces indicated, X "Faces" on each of the corners. Make sure the edge between the two faces is also deleted.

Select the vertex indicated and snap the cursor to it. Shift-S Cursor>Selection. Then select the four vertices from one of the deleted faces.

In front view spin a corner radius with five vertices.
Spin corner radius When all the four corners have been spun Select All and remove doubles W.

Cut loop of vert's We now need the centre line of the flange to position the elongated bolt holes. It can't be loop cut because the corner faces are triangles.

Use the Knife tool (Midpoints) and cut the loop indicated.
Cut Loop to form chamfer To add a chamfer to the edge of the adjuster loop cut Ctrl-R the outer loop of faces. With the Edge Length button activated, slide these to 0.5mm from the edge. Do this on the front and back of the flange.
Now select the front outer edge loop and move it 0.5mm on the Y-axis. Do the same on the back outer edge but move this -0.5mm.

Position Cursor
Snap the cursor to the middle of the two vertices on the left-hand picture.

In front view add a circle, Vertices: 16, Radius: 2.2 (clearance for a 4mm bolt).
Add Circle and adjust for slot
Copy the vertices from the circles centreline and above and move the copy 4mm on the Z-axis. Then copy the vertices of the circle from the centreline and below moving them -4mm on the Z-axis.

Delete vert's
Delete the original circle and the flange vertices closest to it.

This leaves you with the outline of the slot positioned centrally on the flange.

Rebuild Faces Alt-RMB select the vertices of the elongated hole, then Shift-Alt-RMB select the vertices of the flange that surround it. Shift-F to fill the area with faces. Alt-F to beautify the fill and Alt-J to convert to quads.

Copy the new faces and move them 3mm on the Y-axis.

Shift-Alt-RMB select the two elongated slots and loft faces between them F "Skin Face/Edge Loops".

Select all and remove doubles.
Copy slot
Select the vertices central to where the other three slots are required and delete them. Copy the slotfaces and surrounding faces. and use Blenders snap tools to snap the copy to the other locations. (Snap described here)

Completed Adjuster First Rotating the two left-hand copies 180 degrees.

Finally select all and remove doubles to complete the adjuster.
Copy to other V-Roller
Once the flange is complete go back into Global view NumPad / and copy the adjuster to the other V-Roller

Shift-D X -150

The Lead Screw & Roller-nut

WE have now got the locations for the fixed rollers and the adjuster blocks. A few other components are needed on the casting because it will also hold the lead screw roller-nut.

Lead Screw and Nut Roller Nut
I am using an M16 threaded rod as the lead screw and have designed a simple roller-nut based on the V-Roller and axle. It’s simply a series of slots at 2mm pitch to marry in to the M16 thread.

To stop the lead screw from flexing away from the nut a couple of bearings will be located above the lead screw and offset slightly to either side of the centreline. These bearings will use a shortened version of the V-Roller axle.
The roller-nut and bearings will also need to be adjustable, so the brackets that hold them back to the main casting will also need to allow some movement in the Z-axis.

My CNC machine is configured with two X-axis slides, one either side of the table. The Y-axis runs between them forming a bridge type layout. The X-axis therefore also has to locate the mounting points for the Y-axis. If you have a look at the photos of my old machine on the CNC page this will make more sense.

At this stage of the design, things are very flexible, none of the component positions are fixed and it's easy to move things around to optimise their location.

We have now accounted for all the parts of the X-axis, so in  part-2, I will start constructing the main casting around them.

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Casting Part 2 Initial Design >>

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