Introduction to Design Assignment Help

Introduction to Design Assignment HelpThe assignment requires the 3D modelling of a simplified 2-stroke combustion engine as per the assignment brief, this includes modelling of individual components, creating an assembly of the parts in various views as well as producing drawings with design intent of the engine and the individual components.

This is the finished model as an assembly including all components properly constrained. I worked through modelling each component individually and referencing various dimensions and features to other parts of the model using external references.
I began by creating the engine block as I considered this part to be the core part of the assembly, I used the information provided on the assignment brief to dimension the various features of this part. Where dimensions were not included I used the information provided by the other parts as a reference.
An example of referencing dimensions from other parts can be seen on the right, the brief does not include the highlighted dimensions on this part. I used the dimensions from the crankcase which connects to the face of this part in the assembly of the engine.
This was the first sketch I created to form the main body of the engine block. There are a number of different sketch tools available to use, for this one I used a centre point rectangle. By doing this I was able to relate the centre of the rectangle with the origin of the part. I then had to define the rest of the sketch, I used the smart dimension tool to apply the correct line dimensions. The small green symbols represent ‘relations’ these allow you to relate parts of the sketch in order to define the sketch.

All aspects of this sketch are constrained, the highlighted text ‘fully defined’ is an indication of this. Until the sketch is properly constrained the test will read ‘under defined’ and if too many relations or dimensions are used a warning with the words ‘over defined’ will appear.

Once the sketch was complete I then needed to turn it into an extruded base/ boss in order to create the main body. I clicked on the extruded boss/ base feature and selected the sketch. I then set the blind distance of 30 mm and pressed the green tick to accept the changes.
This image shows the preview of the boss extrude.
Extrude Specification window.
Next I needed to remove material from the outside of the main body to create the rounded profile at the back of the engine block. This was a very simple sketch as I snapped the midpoint of the circle to the origin which was located at the centre of the main body, and to define the diameter I made a tangent relation between the circle and rectangle which made the shape of the main body.

These images show the preview of the cut extrude area and the product of the cut extrude.

I then created the sketch and boss extrude for the mounting brackets, I based the sketch upon the top plane and related the centre points to the origin. I dimension ed the width as per the assignment brief and extruded it 3 mm using the ‘mid plane’ direction.

I used the chamber feature to create the required chamber on each end of the mounting brackets. The feature specification allows you to specify the angle and size, I set the angle at 45° and the size at 1 mm.

An important part of creating parts and assemblies is by following best practices of modelling, these allow you to maximise the way you use the various features provided by the Solid works software. As a starting point planes should be taken into consideration, where possible I use the planes as centre points of the model. This allows me to reference the planes when using features such as mirror, revolved base/boss, etc.

This image shows the design tree for the engine block, I aimed to keep this list of features as short as possible. This is done with production intent as the less features such as cuts and holes the less work the will be involved in setting up machinery. I used a range of features and methods to maximise the way the model is controlled with future modifications in mind, this meant that I made the model in a way that allows dimension changes to be made without other aspects of the model being changed.

I renamed various features of different parts depending on the complexity of the part, this allows me to quickly identify areas/ specific features if I need to modify the part.

These are line images of the engine block in isometric view, the various views highlight some of key dimensions of this part. The dimensions are from various sketches which are defined and turned into various features such as extruded boss/ base and cut extrude. It is important to keep in mind the stages at which you decide to use certain features, depending on where a cut is placed in a design tree can change the outcome of the cut. Some of the dimension values have been ‘linked’ this means that I can reference the dimensions in equations or other parts of an assembly at a later point.

There are a number of different ways to use the features but they all follow similar rules and reference points. In this example I have made a cut on the model, instead of specifying the dimension using ‘blind’ I used ‘offset from surface’. I then specified the dimension I wanted the cut to finish away from the selected surface.
The assembly requires M3 bolts to fix two key components to the engine block itself, these bolts locate in the appropriate tapped holes as per the assignment brief. I used the hole wizard feature in order to create these holes, it allowed me to select the Metric standard sizes for an M3 thread as well as the type of hole and depth if applicable. An advantage to using this feature is the hole information is automatically added when creating a ‘hole cal lout’ annotation on the 2D orthographic drawings, any changes made to the hole dimensions are automatically updated on the drawings.

Hole Specification                        Hole Positions                         Hole Cal lout  Annotation

The mirror feature allows you to copy features, faces and bodies and ‘mirror’ them about a face or plane. This feature shows the importance of design intent as if you use the planes of the model correctly you make the modelling process a lot easier when it comes to using features like this.

On the engine block there are 4 M3 clearance holes on the mounting brackets, however using the mirror feature I only needed to define 2 of the holes in the original hole wizard feature. I then selected the right plane which is in the centre of my engine block as a reference and selected the holes as the feature to mirror.

The mirror plane is highlighted in blue, the preview of the new features to be created are highlighted in yellow and the feature ‘M3 Clearance Hole1’ is selected as the feature to mirror about the plane.
I used the fillet tool to create a round profile on the corners of the crankcase mounting face, the fillet tool allows you to select the edges you want to create the fillet on and specify the radius of the fillet.

I took into consideration any changes which may be made to the model later on and related and dimensioned sketches accordingly. When applicable using relations is a much better way of defining sketches as if a dimension change is made to a feature which this sketch is dependent on, then this feature would also change accordingly. The relations highlighted in red (top left image) are coincident relations, changing the dimension highlighted in blue would make the cylindrical boss diameter change as well as the width of the sketch shown.
Planning ahead when modelling parts can save time and effort, applying certain features in a certain order can be used to your advantage, I had a series of different cuts required on the inside of the engine block.

The first in the series of cuts (Cut2) removed the material from the area in which the crankshaft end is located,

This feature was modified at a later date as the distance from surface was too short, the depth of the crankshaft area was decreased in order to prevent the connecting rod from slipping off the end of the crankshaft.

The second in the series of cuts is where the piston, gudgeon pin, and connecting rod are located.
Using the face created by Cut2 I was able to configure the next cut (Cut3) to remove material up to this face, I did this by selecting ‘Up To Surface’ in direction 1 and selecting the face created by Cut2.

I then applied the exact same method as before to carry out Cut4, this is the inlet/outlet of the engine block and it cuts through up to cylindrical face inside the engine block. The selected surface is highlighted in pink and the preview of the cut is outlined in yellow.
I needed to apply a material to the part in order to later use this property as part of my drawing template. The material was not specified in the assignment brief so for the purpose of this I chose plain carbon steel.
With a material now specified I could use the properties of that material to evaluate a weight of a part, at this point of the design they do not seem appropriate, however at a later date I can link these properties to the title block data of the drawing. The linked properties will then automatically display the weight and material of the part on the 2D drawings.

Linked Properties

Setting up this type of sheet format took a bit longer than filling in the information manually, however the sheet format is now set up for future use and this will save time and make any changes update automatically. This is a very useful tool for the purpose of production and modification.

Engine Block Dimensions

The next part I modelled was the connecting rod, this part is very basic and only required 5 features to create.

I started the part with the sketch of the part body, I used a centre line to join two circles at either end a set distance apart. I then dimensioned all diameters accordingly and related the sketch until defined. I made sure that the origin was in the centre of the part as this would enable me to use the mirror feature later on. I used the features extruded boss, cut extrude, mirror and chamfer to model the connecting rod (see below).
The piston is another simple part to model requiring only 4 features to make. I used a Cut Revolve feature to remove the material from the inside of the piston.

The main shape of the piston is defined by a circle, using the origin as a centre point and turning the sketch into an extrude boss feature. The piston diameter is to suit the cylindrical cut inside the engine block.

The following sketch was made on the right plane of the model which is located through the centre of this part. Once I had fully defined this sketch I used it to create a revolved cut. The axis of revolution is highlighted in blue.

I used a cut extrude to remove the material at the side of the pin as per the assignment brief drawings.
I used a cut extrude feature ‘through all’ to create the hole for the gudgeon pin part.
There were a couple of ways I could have modelled the crankshaft, the first way would be to create at least 4 boss extrude features. This would involve drawing 4 different sketches for each different diameter circle. I used a different way which involved the use of a revolved boss/ base.

I created the sketch (shown left) on the top plane of the part, I once again made sure that the origin and any relevant planes were at the centre points of this sketch. This sketch is what forms the main body and shape of the crankshaft. I dimensioned the lines as per the brief where applicable.

The line highlighted blue indicates the axis of revolution, the direction and angle can also be specified in a revolved boss feature.

Modelling the part in this way uses less features in the design tree, this saves times and money when setting up machinery to produce the part.

The link for the connecting rod was created using the sketch on the left, I then used a boss extrude to create the feature (specification bottom right).
In order to create the keyway on the end of the crankshaft, as per the assignment brief, I first needed to insert a plane to sketch on. To do this I clicked: Insert > Reference Geometry > Plane. The following specification window appears.

There are a number of different ways to reference a plane, for this one I selected the top plane of the model, perpendicular, as the first reference. I then selected the cylindrical face which the keyway cut would be on as the second reference, tangential.

Now I had the sketch plane I could create the sketch in the shape and size of the keyway on the assignment brief and use an extruded cut to remove the material.
I then created the fillets: radius 0.5mm, and the chamfers: 0.5 X 45°. These were specified dimensions in the assignment brief.
The crankcase was modelled using the same features to those demonstrated previously. The inside diameter of this part is to suit part of the crankshaft. The Fillet1 feature also matches the radius of the fillets on the engine block, these two components are fixed together using M3 bolts. A hole wizard feature using M3 clearance holes is used to create the holes for these fixings.

I first created the base of the crankcase, this part mates to the engine block in the assembly. The dimensions are identical to the face of the engine block that it mates to including the hole locations.

I then created a sketch along the top plane with the intention of using a revolved boss extrude, this would create the cone shaped body. The dimension R13 is bigger than that specified in the brief, this was due to a change made to the engine block itself. The engine block and connecting rod were interfering so the diameter of Cut2 was increased to 26mm to correct this.
The M3 clearance hole positions were located to the same dimensions as the M3 tapped holes on the engine block. The hole for the crankshaft to pass through was created sketching a circle on the front face, I dimensioned it according to the brief and ensured it was fully defined. Once I had the cut I created a chamfer on the back face: 0.5 X 45°. This is to allow room for the radius of the fillet on the crankshaft.

The Cylinder Head is located on the top of the engine block in the assembly. It is mounted on top of the ‘head’ and is secured using M3 bolts. The clearance holes for these bolts are in the same position as the M3 tapped holes on the head of the engine block.

I used a revolved boss to create the main body of the cylinder head, I used a sketch fillet to eliminate the need to use the fillet feature later on, this reduces the amount of features in the design tree.
I then created a sketch for the extruded cut required to model the part to the design brief, where possible I used the mirror sketch entities feature to save time dimensioning each individual rectangle. To do this you must also insert a centre line (or line) to use as a mirror point on the sketch.

The M3 clearance holes are located to suit the threaded holes on the head of the engine block. The ¼ inch hole for the spark plug is in the centre of the part (looking from above). I therefore related the hole to the origin of the part.

circles, the centre points of the circles are related coincident to the holes already created by the M3 clearance holes and the ¼ Inch tapped hole. The cut is only 7mm deep, this is the same as the cuts already made through the body of the part. Instead of creating another dimension I used the ‘Up to Surface’ option in the hole specification and selected the appropriate face.

The Gudegeon Pin was a very simple part to make, it only required 2 features as shown in the design tree. It was created using a sketched circle was then turned into a boss extrude from mid plane. The purpose of the chamfer is for assembling the parts, the chamfer would make the pin easier to locate inside the piston and the connecting rod in reality.

The pin dimensions are to suit the assignment brief, the chamfer size is 0.25mm X 45°.

The final part I needed to model was the M3 ISO Metric Cap Head Screw. I needed multiple versions of this part as I needed 4 bolts 8mm long and 4 bolts 10mm long. To do this I created a design table, this would allow me to type in values and create any size bolt I needed. The new configurations created can be found in the configurations tab shown below (left).

The first part feature I created was the head of the bolt, as I knew that not all head sizes are the same (larger nominal diameter requires bigger head size) I set up a few equations. I also needed to link the dimension values in order to use them for the equations, this is done by right clicking the dimension and selecting ‘Link Values’, this requires you to name the dimension. For this head diameter dimension I labelled it ‘Head Diameter.This is a list of the equations I made inside the part. This allowed me to simply type in values in my design table which automatically update the model configurations to suit.

Example of Linked ValueThis symbol indicates that the value of this dimension is linked to a value or equation.

I created the cut for the hex key using a sketched polygon (6 sides) on the top face. The dimension across the flats was linked to a value called ‘Socket Size’. This makes it easier to identify when selecting the variables for a design table.

I created the thread of the bolt using a boss extrude of a sketched circle 3mm diameter. I also linked this value so I could use it as a variable in my design table.

I then created the chamfers for both the bottom of the thread and the top of the head. The ∑ symbol represents that the dimension is driven by an equation. I created an equation for these in order to change the size of the chamfer with respect to the thread size and head diameter.
I then had to insert a Helix/Spiral, this would be my reference geometry for the swept cut that would form the thread. I clicked: Insert > Curve > Helix/ Spiral. I then had to sketch a circle at the end of the bolt, I converted the sketch entities from the 3mm diameter circle. I then set the pitch and height of the spiral (bolt pitch dimensions came from Manual of Engineering Drawing, Colin H. Simmons).

I then created the following sketch of the profile of the thread to use for my swept cut feature. The dimensions for this came from the book – Manual of Engineering Drawing, Colin H. Simmons. Using the information in this book I set up equations which relate to the thread pitch, therefore when the thread pitch is changed in the design table, these dimensions change to suit.

I then created the swept cut feature by selected the sketch of the thread as the profile, and the Helix/ Spiral 1 as the path to follow.

After I had created the bolt I then set up the design table referring to the values obtained from the Manual of Engineering Drawing text book. The design table then imports the new created configurations into the part itself. In the assembly I would be able to specify which configuration to use and where.

With all the parts now completed I needed to create the assembly. The overview of the design tree shows I have organised the parts into various folders, this is to allow me to identify various components easily and tidy up the appearance.

This is a view of the parts inside the design tree, it shows all of the modelled parts under Components, the M3 bolts I created are in the folder called Fixings and any other features used are in the Assembly Features folder.

The Assembly is properly constrained as it is fully defined. This only applies to TDC and BTC configurations as the crankshaft, piston and connecting rod are free to move in the default configuration.

This is a list of the mates used in the assembly in order to constrain the model appropriately.

I used a derived hole pattern to pattern one M3 bolt to another 3 positions. I selected the M3 bolt as the component to pattern and the M3 tapped hole on the engine block as the driving feature, this then creates new copies wherever this feature appears.

I used the same method as before to create another derived hole pattern, this time the component to pattern was the M8 x 10 configuration of the M3 Bolt. The driving feature was the M3 tapped holes in the head of the engine block.

I created an exploded view of the assembly to use on my 2D production drawings. This will give a much better overview of how the components are assembled together.
I also updated the properties of the assembly, all of the existing properties from the parts such as weight combine together in the assembly to give a total evaluated weight. I edited the material to read ‘SEE PARTS’, this is because of the type of border template I have set up in my 2D drawings. Instead of not specifying a material in the assembly, it will refer the assembly drawing materials to other individual part drawings.

I created a second display state in order to change the transparency of the selected components. The purpose of this display state is to see the internal parts of the assembly in the different configuration settings.

Maddox Smith

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