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Dimensions, Tolerance and Assemblies - Coggle Diagram
Dimensions, Tolerance and Assemblies
Dimensioning
9 Types of Dimensioning:
- Parallel Dimensioning (Datum Dimensioning) : Consists of several dimensions originating from a common reference surface aka the datum.
- Superimposed Running Dimensioning: Simplifies parallel dimensions in order to reduce the space used on a drawing
- Chain Dimensioning: Should only be used if the function of the object would not be affected by the accumulation of the tolerances
- Combined Dimensioning: Uses both chain and parallel dimensioning
- Dimensioning Small Features: Placing the arrows heads between the extension lines make it hard to read the dimension so the arrow heads can be placed outside the extension lines
- Dimensioning of Multiple Features: To dimension multiple same dimensions, we use (N x Dimension)
- Dimensioning of Radius: Its dimension starts with "R".
- Dimensioning of Circle, Arc & Hole: A circle is dimensioned by its diameter. An arc is dimensioned by its radius. The holes are located by their centerlines
- Dimensioning Angles: It is marked with a curved dimension line and has the degree symbol.
Rules of Dimensioning:
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4) The dimension lines, extension lines and object outlines should not cross or overlap
Tolerance
3 Types of Tolerance:
1) Bilateral Tolerance: Allowed to vary in 2 directions from the specified dimension and both dimensions need not vary by the same amount
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Clearance Fit:
EG: Shaft to be place in the hole. We calculate the max shaft diameter = 49.7. Then we calculate the minimum hole diameter = 49.9. Thus, this is called the Clearance fit as the shaft can fit into the hole even if there's tolerance.
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Interference Fit:
EG: If the minimum shaft diameter is 49.8 which is larger than the maximum hole diameter of 49.5, it wouldn't find thus this will be an Interference fit.
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How it works?
Begins with brining in a base component, selected because of its central role
Each component brough in needs to be oriented & located relative to other components in the assembly. The assembly joints are used between elements or components
Types of Joints
- Rigid joints fixes 2 components to one another and it provides no degrees of freedom.
- Revolute joints has single translational degree of freedom like a hinge and can rotate around the standard X,Y or Z axis or around an edge in the model (custom axis)
- Slider joint has single translational degree of freedom and is used for components that slide along one another.
- Cylindrical joint provides 2 degrees of freedom: 1 translational & 1 rotational. Components joined with this joint always rotate around the same axis.
- Pin slot joint also allows 2 degrees of freedom like Cylindrical joint but the components can rotate around different axes.
- Planar joint allows 3 degrees of freedom and it allows 2 directions of translation in a plane and a single rotational direction normal to that plane. It is useful for joining 2 components so they can rotate while sliding across the plane.
- Ball joint has 2 degrees of rotational freedom: pitch & yaw. Pitch allows components to rotate around the Z axis while Yaw, rotates components around the X axis.
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