# A Tolerance Type Screening Method Based on Similarity Evaluation
## 3 Similarity Assessment Strategies
### Tolerance Specification Scheme  
The core of tolerance specification design is to make the tolerance specification scheme of a part conform to the functional requirements (e.g., geometric tolerance requirements) of the assembly. Where geometric functional requirements are the basis for meeting other functional requirements. The similarity assessment method for screening tolerance types proposed in this paper is related to the basis and process of determining the tolerance type of a part, on the basis of which a tolerance specification case is constructed. The process for determining the tolerance type of parts is depicted in Figure 1. Taking the shaft sleeve in Figure 2 as an illustrative example, the process of determining the tolerance type is concisely elucidated. Analyze the features of each component element of the product and determine the tolerance elements. Determine the datum framework: Analyze the assembly relationships of the product, establish the topological spatial relationships of the tolerance elements, and define the datums of the tolerance elements. First, identify the feature elements of the part that require tolerance design (referred to as tolerance elements in this paper). This bashing has six assembly feature surfaces: planar surfaces \(\mathbf{g}_{1}\), \(\mathbf{g}_{3}\), and \(\mathbf{g}_{5}\), external cylindrical surfaces \(\mathbf{g}_{2}\), \(\mathbf{g}_{4}\), and internal cylindrical surface \(\mathbf{g}_{6}\). The main function is to rotate and seal. \(\mathbf{g}_{3}\) and \(\mathbf{g}_{4}\) are the main working surfaces that connect the seals. In this example, the \(\mathbf{g}_{3}\) feature surface is selected as the tolerance feature element. Figure 1: Flowchart for determining tolerance types. Establishment of datum reference frame: Usually, the axis of shaft parts is chosen as the datum reference frame. According to the functional characteristics of the needs and dimensional characteristics, in Figure 1, the natural choice of the axis of the cylindrical surface \(\mathbf{g}_{2}\) to establish the datum reference frame \"\(A\)\"; the root assembly seals of the work characteristics, the need to determine the direction of the position between the two tolerance elements of the \(\mathbf{g}_{3}\) and \(\mathbf{g}_{4}\) needs, according to the relative size of the relationship between the selected axis of the outer cylindrical surface \(\mathbf{g}_{2}\) as a reference frame of reference \"\(B\)\". Determine the tolerance type of all tolerance elements: tolerance element \(\mathbf{g}_{3}\) plane, ideal direction position perpendicular to the reference datums \"\(A\)\" and \"\(B\)\", optional shape tolerance is flatness, relative to the datum \"\(A\)\" optional tolerance types are perpendicularity, positional degree, end face runout, end face full runout. Considering the functional requirements, full runout of the end face under reference \"\(A\)\" and perpendicularity under reference \"\(B\)\" are selected for \(\mathbf{g}_{3}\). Element \(\mathbf{g}_{3}\), the basic elements for describing tolerance type problems are a tolerance element (\(\mathbf{g}_{3}\)), a part containing the characteristics of the tolerance element and all its constituent elements, and the spatial topological relationship between the tolerance element and the reference datum. The strategy for solving the problem is described as a benchmark framework (\"\(A\)\" and \"\(B\)\") with tolerance types (full-face runout and squareness). According to the tolerance standards ISO 1101 [24] or ASME Y14.5 [23], the reference frame for the datum includes single datum, double datum, and triple datum. Based on the above analysis, formally, \(\mathbf{T}_{\text{df}}\), \(\mathbf{T}_{\text{ds}}\), and \(\mathbf{T}_{\text{dt}}\) are used to represent the first, second, and third benchmarks of tolerance elements, respectively.