How do you use geometric dimensioning and tolerancing (GD&T) in DFA?

1 What is tolerance and clearance?

Tolerance and clearance are two related concepts that describe the allowable deviation of the parts from their nominal or ideal values. Tolerance is the difference between the maximum and minimum dimensions of a part, such as its length, width, or diameter. Clearance is the gap or space between two mating parts, such as a shaft and a hole. Tolerance and clearance affect the quality, performance, and reliability of the product, as well as the ease and cost of assembly.

2 Why are tolerance and clearance important in DFA?

Tolerance and clearance are important in DFA because they influence the fit, function, and alignment of the parts. The fit is how tight or loose the parts are when they are assembled. The function is how well the parts perform their intended tasks. The alignment is how well the parts are oriented and positioned relative to each other. Ideally, the parts should have a fit that allows easy assembly and disassembly, a function that meets the design requirements and customer expectations, and an alignment that minimizes errors and defects.

3 How to choose the right tolerance and clearance for DFA?

Choosing the right tolerance and clearance for DFA depends on several factors, such as the type of fit, the function of the parts, the manufacturing process, and the quality standards. Generally, the tighter the tolerance and clearance, the better the fit, function, and alignment of the parts. However, tighter tolerance and clearance also increase the difficulty and cost of manufacturing and assembly, as well as the risk of rejection and rework. Therefore, the tolerance and clearance should be optimized to achieve a balance between quality and cost.

4 How to use GD&T in DFA?

GD&T is a system of symbols and rules that define the geometric characteristics and tolerances of the parts. GD&T provides a clear and consistent way of communicating the design intent and the assembly requirements to the manufacturers and assemblers. GD&T can help to reduce ambiguity, errors, and variations in the parts and their assembly. GD&T can also help to improve the efficiency and accuracy of inspection and measurement.

5 What are some examples of GD&T in DFA?

In Design for Assembly (DFA), GD&T can be used to specify the location and orientation of a hole relative to a datum or reference point, the shape and size of a surface or feature, the variation of a circular or cylindrical part when it is rotated, and the deviation of a surface from a perfectly flat plane. This ensures that the hole is aligned with the shaft that will be inserted into it, the surface or feature conforms to the desired contour and dimension, the part has a smooth and uniform motion, and the surface is level and parallel to another surface or datum.