Please enable JavaScript.
Coggle requires JavaScript to display documents.
Dimensions, Tolerances & Assemblies - Coggle Diagram
Dimensions, Tolerances & Assemblies
Dimensions
In a Drawing
- Dimension Text (Unit)
- Tolerance (how much the dimension is allowed to deviate)
- Dimension Line (arrowhead on each end)
- Extension Line (continue extend from surface and establish size of dimension)
- Extension Line Offset (a gap between the object surface and the extension line, so it is not confused with visible lines of the model)
-
Rules of Dimensioning
- Dimensions should not be duplicated, i.e. same dimension should not be repeated in different views.
- Avoid dimensioning to hidden lines and features.
- Dimension lines, extension lines and object outlines should not cross or overlap.
- Dimension and drawings must be neat.
- Dimension features or surfaces should be done to a logical reference point
Tolerance
The Importance of Tolerance
In practice, parts cannot be manufactured exactly to the dimensions stated in the drawing, due to manufacturing variations. Tolerances are included with dimensions in engineering drawings to take into account these manufacturing limitations.
Types of Tolerance
-
-
Bilateral Tolerance
Allowed to vary in two directions from specific dimension. Both directions need not vary by the same amount.
-
Clearance Fit
Example,
Maximum shaft diameter = 49.7
Minimum hole diameter = 49.9
From here, we can see that there will always be sufficient clearance for the shaft to interface with the hole. In such a scenario, we will have a clearance fit.
Interference Fit
Minimum Shaft Diameter = 49.8
Maximum Hole Diameter = 49.5
This will be a interference fit.
Assembly
What is Assembly Modelling?
In an assembly model, multiple parts are brought together to define a larger, more complex product representation. Assembly modelling facilitates the collaboration among designers, engineers, manufacturing technicians and others to ensure a product assembly works. Individuals in different disciplines can work concurrently, resulting in faster and less costly delivery of products to market.
How Assembly Modelling Works?
Constructing an assembly normally begins with bringing in a base component, selected because of its central role. Each component brought in needs to be oriented and located relative to other components in the assembly. Assembly joints are used between elements of components.
In Fusion 360, multiple parts can be created and assembled in the same file. In many other CAD software, there will be individual part files, and an assembly file to place all parts together.
Types of Joints
- Rigid
- Revolute
- Slider
- Cylindrical
- Pin Slot
- Planar
- Ball
What is Assembly Drawing?
An assembly drawing is a drawing of various parts of a machine or structure assembled in their relative working positions.
An assembly drawing shows,
- a list of all the parts of components (part list or Bill of materials, BOM)
- the general arrangement of these components
- how they fit together, and
- the overall dimensions - but not the specifics
How to use Tolerance in Fusion 360
- Create 3D models and save
- Create Drawings
- Double click on dimension to specify tolerances
- Save drawings
Application of Clearance and Interference Fits
In clearance fit, there would still be an allowance for two parts to move, such as in a door hinge.
In interference fit, it would be difficult to move (or remove) the two interfacing parts. Usually, a lot of force is needed to remove the two parts. Examples are shafts that are fitted through bearings, so that the shaft does not slip.