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          Blender Tutorials: Designing a Casting - part 3

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Designing a casting. Part 3 Roller-nut Mounting Brackets

To finish off all the mounting locations on the casting, we need three more components, the mounting brackets for the Roller-nut and support bearings. Because the design of the brackets relies on the position of the casting face from the axle centres and also any pockets in the casting, it has not been possible to design the brackets until now.

Hide all the components other than the Roller-nut assembly, casting and lead screw. It will be easier to see the available space for the bracket without the other components.

Tab into Edit Mode for the casting and snap the cursor to the front face. I have selected the two vertices of the recess, so the cursor is on the edge of the recess and aligned with the mounting face of the axle.
Roller-nut Assembly

Roller-nut Adjuster

Bracket Mounting Back in Object Mode, add a Plane. Scale the left-hand side vertices to the cursor, its height to 30mm and width to 4mm. Extrude the right hand vertices on the X-axis 6mm then again on the X-axis 10mm, the 6mm section will be used to form a locating key, the 10mm section will become the bolt flange.

Extrude the three faces to give a thickness of 3mm.
Centre Boss Tab into Edit Mode for the axle and snap the cursor to the vertices on the flange fillet as detailed in Part 1. Tab back into the adjuster Bracket.

In side view add a circle with 32 vertices and a 3mm radius.

Extrude these vertices then press 

Construct Face Delete some of the vertices from the outer circle and add edges back to the mounting flange. With careful choice you can get a tangential alignment. 

Midpoint cut a row of vertices on the mounting flange and delete the vertex that would become inside the bracket. This will remove four faces from the mounting.
Rebuild new faces around the hole.
Extrude to form face Select the vertices indicated and Extrude them on the X-axis 4mm then again 6mm.

In wire view delete the vertex that has been created internal to the bracket. Select all and remove doubles.
You will also need to rebuild the faces of the original face, as these will be removed by the extrusion process.

Add elongated bolt holes As detailed in Part-1 for the V-roller adjuster brackets add two elongated holes to the flange and also a fillet to the outer corners.

Finally the bracket needs to be constrained to a movement perpendicular to the leadscrew.
Add Key To achieve this I have purposefully created vertices that will allow the incorporation of a key, which will be located in a slot machined into the face of the casting.

Select the two faces indicated and extrude them 2mm.

Support Bearing Adjusters.

Adjuster The support bearing adjusters are modelled in a similar way to the Roller-nut adjuster bracket. I have slimmed down the bracket to 6mm and moved the mounting flange above the bearing.

The right hand adjuster will be set back into the pocket provided in the casting.
Adjuster Penetration The view from the back shows the 6mm key, which penetrates the face of the casting.

Some work will be required to provide the mating slot in the casting and the bolt holes.

Adjuster 2 The left-hand adjuster stands out further from the casting to allow support forward of the leadscrew centreline.

Transferring Geometry to the Casting

Back face of adjuster Select an adjuster and Tab into Edit Mode. In top view NumPad 7 select the vertices on the back face of the adjuster.
Copy the vertices Shift-D then Escape to leave the copy in place. Separate the copy from the adjuster mesh P.

Tab into Object Mode and select the copied adjuster face, then Shift-RMB select the casting. Join the copied face to the casting Ctrl-J.

Repeat this for all three adjuster brackets.

Some work is now needed to modify the copied geometry to suit the casting.
Adjuster Geometry

As with the V-roller adjuster, the lead screw adjusters will be secured with 4mm bolts, so the casting needs 4mm-tapped holes centrally to the slot.

Again these will be represented by a hole at the tapping drill size, which is 3.3mm.

Alt-RMB Select the vertices from the slot and snap the cursor to their centre. Add a circle with 16 vertices and a radius of 1.65mm. Repeat this for all slots.
Centre tapped hole

Increase length of slot Delete the unnecessary vertices, leaving the keyway slot and tapped hole circles.

In order for the adjuster to move in the slot the slot length needs to be increased by at least the amount of
movement available on the elongated bolt holes. Grab the top vertices of the slot and move them on the Z-axis 5mm.
Elongate slot I have also cut the slot lengthways with a mid point cut. This has enabled me to spin a radius at the top of the slot, which on the casting will be cut using a 6mm slot drill, giving the radius on the ends.

A mid point cut has also been made horizontally across the recess to align vertices with the centre vertices of the key slot.

Face Penetration The slot on the top right adjuster poses a different problem, as it has to penetrate the face of the bearing recess.

To add vertices and edges for this penetration use the Geom tool. Select the intersecting faces and  in a script  
window choose Scripts>Mesh>Geom Tool

Select Intersect: Face(s) (Cut)
Intersect Cut The Geom Tool will cut a new series of edges around the intersection. It will also triangulate all the selected faces.

Delete all the unnecessary faces and convert the remainder to quads, Alt-J.

Completed Slot Extend the top of the slot 5mm to allow the adjuster bracket room to slide.

Cut a vertical row of vertices down the slot and bearing recess, using the knife with a mid point cut.

Spin the top radius.
Left Hand Slot The left-hand adjuster slot just needs to be extended 5mm top and bottom.

A vertical mid point cut will allow the ends to have a radius spun to match the slot width.

All the mating geometry needed to complete the casting has been accurately extracted from the component assembly.

In the next part I will complete the casting by building faces between all the extracted geometry elements.
Casting Geometry

<< Casting Part 2 Initial Design Tutorials Casting Part 4 Finishing Off >>

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