CAD Modelling
CAD Modelling
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3D CAD (Computer-Aided Design) modelling is an exciting and essential tool in the world of design and engineering. It allows us to create detailed, accurate, and visually engaging digital representations of objects, from simple shapes to complex structures. Using specialised software, we can bring our ideas to life in three dimensions, experiment with designs, and refine them before they are ever made in the real world. Whether it’s designing a product, planning a building, or exploring creative concepts, 3D CAD modelling combines technical skills with creativity, making it a vital skill for modern industries and an excellent way to express your innovative ideas.
Modelling Tree
Modelling Tree
The modelling tree, located on the left-hand side of your screen in Autodesk Inventor, stores all your previous work, including sketches and features. It allows you to revisit and edit sketches or models without the need to delete or start anew. You can also rearrange your work or temporarily disable a feature by suppressing it.
There are numerous advantages to using the modelling tree; for instance:■ It saves time, as you do not need to redraw or model again. Instead, you can modify that feature directly in the modelling tree■ If you make a mistake further along in the process, you do not need to undo your work. Instead, you can edit that specific section■. By using suppress, you can turn off certain features to concentrate on previous stages.
There are numerous advantages to using the modelling tree; for instance:■ It saves time, as you do not need to redraw or model again. Instead, you can modify that feature directly in the modelling tree■ If you make a mistake further along in the process, you do not need to undo your work. Instead, you can edit that specific section■. By using suppress, you can turn off certain features to concentrate on previous stages.
Work Planes
Work Planes
Work planes are like digital sheets of paper where you create 2D sketches. Most 3D CAD software gives you three main work planes to start with: one for the elevation (front view), one for the end elevation (side view), and one for the plan (top view). You should choose the right work plane before starting your sketch.
You can also add extra work planes to your model to help with more advanced designs or to sketch on curved surfaces.
You can also add extra work planes to your model to help with more advanced designs or to sketch on curved surfaces.
Axis
Axis
When sketching, you will always see the axis you are drawing on. Sketching happens on two axis lines at a time, like X and Y. To turn your sketch into 3D, you use the third axis, Z. These three axes—X, Y, and Z—help you create 3D models.
2D Tools
2D Tools
Line
It enables you to draw straight lines.
Circle
It enables you to draw circles.
Ellipse
It enables you to draw ellipses.
Rectangle
It enables you to draw a four-sided shape like a rectangle or square. A two-point rectangle will start drawing from the corner, whereas a two-point centre rectangle will enable you to draw from the centre.
Arc
It enables you to draw arcs/ curved lines.
Polygon
It allows you to create polygon shapes like triangles, pentagon hexagons, or octagons.
Chamfer
A chamfer can be used in a 2D sketch or applied to a 3D model. This action cuts the corner of your shape, creating an angle. It defaults to 45 degrees however this can be changed depending on the model.
Fillet
A fillet can be used in a 2D sketch or applied to a 3D model. This action curves the corner of your shape.
Copy
Enables you to replicate a shape or sketch without needing to redraw it.
Trim
Using trim will allow you to remove any excess lines or portions of a shape, provided that another line interacts with it.
Rotate
It allows you to turn your sketch around.
Mirror
The mirror duplicates a sketch across a work surface or axis of your choosing.
Extend
Adds lines to fill a gap in a sketch.
Offset
Offset enables your shape to be replicated on either the outside or the inside of the original shape.
Project Edge
You can project geometry to copy an edge, line, or face onto a new 2D sketch.
Linear Array
A linear array can be used in a 2D sketch or a 3D model to repeat elements a specified number of times along a line/axis.
Radial Array
A radial array can be used in a 2D sketch or a 3D model to repeat elements a specified number of times in a circle to a chosen degree.
Box Array
A box array can be used in a 2D sketch or a 3D model to repeat elements a specified number of times in the shape of a box/rectangle.
Extrude
Extrude
Extrusions are 3D models that maintain a uniform shape and consistent thickness throughout their entire length. The thickness and shape remain the same from the bottom to the top. They are often used to create objects such as cylinders or blocks.
Profiles can be extruded in three directions:
Extrude subtract is used to cut away material from a 3D model. It works by pushing a shape through the model, removing any material in its path. This is useful for creating holes, slots, or other cut-out shapes in your design.
Profiles can be extruded in three directions:
- Above the workplane
- Below the workplane
- Symmetrically through the workplane
Extrude Subtract
Extrude subtract is used to cut away material from a 3D model. It works by pushing a shape through the model, removing any material in its path. This is useful for creating holes, slots, or other cut-out shapes in your design.Extrude Subtract
How to answer an extrude question
How to answer an extrude question
- PROFILE - Describe how to sketch out the 2D shape.
- DIMENSION- Provide the dimensions for the 2D profile.
- COMMAND - Identify the 3D modelling command extrude.
- DIMENSION - Provide the size for the extrude.
Extrude Subtract
Extrude Subtract
- PROFILE - Describe how to sketch out the 2D shape that will be cut out.
- DIMENSION - Provide dimensions for the 2D profile.
- COMMAND - Identify the 3D modelling command extrude subtract.
- DIMENSION - Provide the dimensions for the 2D profile.
Revolve
Revolve
Revolve is used to create cylindrical, symmetrical 3D shapes.
To do this, you must have two items:
You can choose to spin it fully all the way around for a complete shape or just part of the way for an open design.
To do this, you must have two items:
- A 2D profile, which is half of the shape you wish to model
- An axis for the profile to rotate around
You can choose to spin it fully all the way around for a complete shape or just part of the way for an open design.
How to answer an revolve question
How to answer an revolve question
- PROFILE - Describe how to sketch out half of the shape.
- DIMENSION- Provide the dimensions for the 2D profile.
- COMMAND - Identify the 3D modelling command revolve.
- DEGREE OF ROTATION - Identify if it is a full revolve (360 degrees), a revolve to next or if the shape should be revolved to a specific degree.
- AXIS - State which axis (line) to use for the revolve. Remember to identify it on your sketch.
Chamfer and Fillet
Chamfer and Fillet
As discussed in the 2D tool section, chamfer and fillet can be applied to a 2D sketch or a 3D model.
Both features enable you to modify the edges of a 3D object. Multiple edges can be selected simultaneously.
A chamfer will create an angle on your model, whereas a fillet will make a curve.
Both features enable you to modify the edges of a 3D object. Multiple edges can be selected simultaneously.
A chamfer will create an angle on your model, whereas a fillet will make a curve.
Shell
Shell
Shell is used to make a 3D model hollow, like the inside of a box or a cup. The hollow space follows the shape of the outside of the model. You need to choose how thick you want the walls to be. You can also remove a surface to create an opening, like cutting the top off a box.
It's important to add any fillets or chamfers before applying a shell.
It's important to add any fillets or chamfers before applying a shell.
How to answer a shell question
How to answer a shell question
- You will likely need to explain how you made the original model (extrude, extrude, subtract or revolve).
- COMMAND - Identify the 3D modelling command shell.
- DIMENSION - Provide the wall thickness for the shell.
- REMOVE SURFACES - Identify if any surfaces need to be removed.
How to work out a shell
How to work out a shell
There are two ways to find out what size your wall thickness will be:
The first method indicates the wall thickness on the orthographic, revealing the size of your shell. No calculations are required; you simply note what is displayed.
The second method involves reading the dimensions and performing the calculations. You subtract the inner edge from the outer edge and then divide the result by 2. For example, the outer circle measures 25mm, while the inner circle measures 21mm, resulting in a difference of 4mm. We then divide 4mm by 2 to obtain a total wall thickness of 2mm.
Sketching on a curved surface
Sketching on a curved surface
To sketch on a curved surface, you need to create a flat work plane. Your work plane may be in the centre of the model, or you may need to offset it to the correct position to draw your shape. After that, you can use extrude, extrude subtract, or revolve to add or subtract material from the model.
Array
Array
An array command allows you to repeat profiles or features without redrawing them.
There are also two ways to use the array tools:
Using an array can save a considerable amount of time in redrawing profiles and features. Because you don’t have to redraw profiles, it enhances accuracy in modelling complex features.
Box array – repeating in a ‘square’ patternLinear array – repeating in a line vertically or horizontallyRadial array – repeating in a circular pattern.
There are also two ways to use the array tools:
- an array of a sketched profile (2D tool)
- an array of completed 3D features.
Using an array can save a considerable amount of time in redrawing profiles and features. Because you don’t have to redraw profiles, it enhances accuracy in modelling complex features.
Box array – repeating in a ‘square’ patternLinear array – repeating in a line vertically or horizontallyRadial array – repeating in a circular pattern.
Intersect
Intersect
Intersect creates a new shape by keeping only the parts where two objects overlap. It removes everything else. For example, if you have two shapes that cross over each other, intersect will keep the area they share and get rid of the rest. This is useful for creating complex models where you only need the overlapping section of two shapes.
CAD Library
CAD Library
A CAD library is a collection of commonly used components that designers can utilise as often as needed. These components can be imported into a design and adjusted if necessary. For example, IKEA would have all their standard fittings, such as screws and bolts, stored in a CAD library, enabling their designers to use them when designing new furniture quickly, without the need to recreate them from scratch.Advantages:■ Saves time and effort by avoiding the need to redraw the same item repeatedly.■ Ensures components comply with proper drawing standards, which is vital when accuracy is critical.■ The components remain the same, thus reducing the likelihood of errors and improving consistency.
- Drawings are standardised as all languages can understand them.
- There is often a cost involved in accessing public CAD libraries.
- You may not always discover precisely what you desire, as CAD libraries contain numerous different models.
Examples
Examples
Describe, using the correct dimensions and 3D CAD modelling terms, how you would use 3D CAD software to model the body. You may use sketches to support your answer. (4 marks)
Answer
- Draw a profile to the dimensions shown. (1 mark)
- Revolve the profile 360 degrees on the centre axis. (1 mark)
- On the top of the model, draw a circle to 20mm and extrude it by 12mm. (1 mark)
- Turn on a workplane in the centre of the model and sketch a rectangle to the dimensions shown. Extrude add the rectangle symmetrically by 100mm. (1 mark)
A 2D logo is added to the bottom of the base. To create the logo a number of 2D CAD drawing tools were used. State the name of the single CAD drawing tool used at each stage. (5 marks)
Answer
- Line
- Trim
- Mirror
- Rotate
- Scale
Describe, using the correct 3D CAD modelling techniques, how stages 2 and 3 of the 3D model are created. You do not need to refer to dimensions in your answer. You may use sketches to support your answer. (5 marks)
Answer
Stage 1 to Stage 2: Sketch a circle on the top of the cube (1 mark)Extrude add the circle (1 mark).
Stage 2 to Stage 3:Turn on a work plane that runs down the middle of the cube. Draw a square and extrude it symmetrically in both directions. Use fillet to curve the edge.
Stage 2 to Stage 3:Turn on a work plane that runs down the middle of the cube. Draw a square and extrude it symmetrically in both directions. Use fillet to curve the edge.
2D CAD tools were used to create the mouth feature on the head component. State the name of the single 2D CAD tool used in each stage. (3 marks)
Answer
- Circle
- Line
- Trim
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