Copyright Goodheart-Willcox Co., Inc. 174 AutoCAD and Its Applications—Advanced Solid Model History Solid Model History AutoCAD can automatically record a history of a composite solid model’s construc- tion. A composite solid is created by a Boolean operation or by using the SOLIDEDIT command. The retention of a composite solid’s history is controlled by the History property setting in the Solid History category of the Properties palette. By default, the History property is set to None. Refer to Figure 8-1. This means that the history is not saved and that edges, vertices, and faces of solids can be directly edited. If the History property in the Properties palette is set to Record, the solid history is “recorded,” or retained. This allows you to work with the geometry used in modeling operations to create the composite solid. Depending on your modeling preferences, it is generally a good idea to have the history recorded. Then, at any time, you can graphically display all of the geometry that was used to create the model. The retention of solid model history for newly created composite solids is controlled by the SOLIDHIST system variable. By default, the SOLIDHIST system vari- able is set to 0. This means that all new solids have their History property set to None and solid history is not recorded. If the SOLIDHIST system variable is set to a value of 1, all new solids have their History property set to Record and solid history is preserved. With either setting of the system variable, 0 (None) or 1 (Record), the Properties palette can be used to change the setting for individual solids. The current setting of the SOLIDHIST system variable is indicated by the Solid History button located in the Primitive panel of the Solid tab on the ribbon. See Figure 8-2. With a default setting of 0 (None), the Solid History button has a white background. Picking this button when it has a white background changes the background color to blue and sets the SOLIDHIST system variable to 1 (Record). To view the graphic history of a composite solid, set the Show History property in the Properties palette to Yes. All of the geometry used to construct the model is displayed. If the SHOWHIST system variable is set to 0, the Show History property is set to No for all solids and cannot be changed. If this system variable is set to 2, the Show History property is set to Yes for all solids and cannot be changed. A SHOWHIST setting of 1 allows the Show History property to be individually set for each solid. This is the default setting. An example of showing the history on a composite solid is provided in Figure 8-3. In Figure 8-3A, the model appears in its current edited format. The History property Figure 8-1. The Properties palette can be used to change many of the properties of a solid. Type of object selected Selected property to modify Category History settings Properties within the category