Lesson 6 engineering
Parallels dimensioning
consists of several dimensions originating from a common reference surface (also known as a datum)
Tolerance
Due to manufacturing differences, items cannot be fabricated exactly to the dimensions specified in the drawing. To account for these manufacturing constraints, tolerances are incorporated with dimensions in engineering drawings.
If no tolerance is specified, the pieces must be measured precisely. The rejection rate will be extremely high and unrealistic.
The same parts can be manufactured by multiple businesses and must be interchangeable. Tolerance ensures good quality control for parts from many manufacturers.
types of tolerance
Bilateral Tolerance: allowed to vary in two directions from the specified dimension. Both directions need not vary by the same amount.
Unilateral Tolerance: allowed to vary in only one direction
Limit Tolerance: the upper and lower limits of the dimension are specified
Tolerance = Upper limit – Lower Limit
Tolerance = Upper limit – Lower Limit
Tolerance = Upper limit – Lower Limit
Clearance Fit
Interference Fit
If the minimum shaft diameter is 49.8 millimeters, which is larger than the maximum hole diameter of 49.5 millimeters. As a result, this would be an interference fit.
If the maximum shaft diameter is 49.7 while the minimum shaft diameter is 49.9. We can see that there will always be enough space between the shaft and the hole. In this case, we will have a clearance fit.
types of joints
Rigid
revolute
slider
cylindrical
pin slot
planar
ball