180 Print Reading for Industry Copyright Goodheart-Willcox Co., Inc. arc, a location dimension must be given for the center axis of the hole, which coincides with the rounded corner axis. Even though this is the design intent, under close inspection the axis of the hole and the axis of the curved surface may not perfectly coincide. In summary, the guidelines in this section have been recommended throughout the years to help drafters create clear, concise size descriptions on drawings. There are too many special cases to cover within the scope of this text. Therefore, if a feature does not have a dimension or it appears a dimen- sion is missing, the print reader should not make an assumption or measure the drawing for critical information. Simply put, dimensions should never be calculated or assumed. Omissions should be reported to the department responsible for the prints. Additional Dimensioning Techniques On a dimensioned drawing, there are usually both size and location dimensions. Size dimensions indicate the size of the part and the size of its various geometric features, such as holes, fillets, and slots. Location dimensions indicate the loca- tion of features such as holes, slots, and grooves. As mentioned earlier, reference dimensions are occasionally given on drawings to assist in knowing certain general distance information, like the basic total size of a feature or sum of dimen- sions. Reference dimensions are not toleranced and are not to be used for layout, machining, or inspec- tion operations. These dimensions are marked by parentheses or, according to older standards, fol- lowed by REF, Figure 9-14. According to Y14.5, the use of reference dimensions on a drawing should be minimized. Tabular dimensions are placed on the drawing as reference letters within the dimension lines. A table on the drawing lists the corresponding dimen- sions, Figure 9-15. Tabular dimensions are useful when a company manufactures a series of sizes of an assembly or part. With this system, more than one part can be featured on a single drawing. Another use for tabular dimensions is dimen- sioning a part with a large number of repetitive Goodheart-Willcox Publisher Figure 9-13. Features with rounded ends provide many choices for dimensioning. 2X .400 R.500 1.450 .906 1.188 .875 .625