tailieunhanh - Dimensioning and Tolerancing Handbook Episode 3 Part 3

Tham khảo tài liệu 'dimensioning and tolerancing handbook episode 3 part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 19-12 Chapter Nineteen Position Using Centerplane Datums Fig. 19-8 shows a simultaneous gaging requirement for a four-hole pattern and a larger center hole. Each uses exactly the same datums in the same order of precedence with the same material condition symbols after the datum features. This creates the simultaneous gaging requirement. This is a very sequential geometric product definition. Figure 19-8 Position using centerplane datums To understand the requirements one might first look at the configurations and ignore the feature control frames. All four holes are shown centered to the hole in the middle and to the outside of the workpiece. The four holes are dimensioned 23 mm from each other but since they are depicted centered to the center hole we must assume each of the four holes is desired to be mm from the center hole and from the middle of the workpiece. The hole in the center is exactly that a hole we desire to be in the middle of the workpiece. The part is then geometrically toleranced in four steps. Step 1 the primary datum feature is identified and given a flatness tolerance. Step 2 the secondary datum feature is identified as one of the 35-mm widths creating a centerplane datum and the datum feature that generates that centerplane is given a perpendicularity control back to the primary datum plane. Step 3 the tertiary datum feature is identified as the other 35-mm width creating a third datum plane which is also a centerplane datum. The datum feature that generates that centerplane is given a perpendicularity control back to the primary datum plane and the secondary datum centerplane. Step 4 is the simultaneous positional requirement of all five holes to each other and to the primary secondary and tertiary datum features. All geometric tolerances of perpendicularity and position are referenced at maximum material condition and use their datum features of size at maximum material condition. This makes it easy to represent each at a .