Dimension marking is a very important link in the process of drawing design. Because the main function of graphics is to express the shape of an object, the real size of each part of the object and the exact position between the parts can only be expressed by dimensioning, therefore, without correct dimensioning, the drawn drawings are meaningless for machining and manufacturing. Below, I sorted out the skills of CAD dimensioning in mechanical engineering drawing, hoping to help you!
After drawing the picture, you can mark it. If the dimensioning style is not set in advance, it will take a lot of time to mark, even many symbols you need can't be marked, and even you have to borrow other software symbols and paste them into the picture, which is time-consuming and laborious and irrelevant. By setting the dimension style, when labeling, you only need to select the matching dimension style, and labeling will be easily completed. As shown in figure 1, the dimensioning style consists of seven items: straight line, symbol arrow, text, adjustment, primary unit, conversion unit and tolerance.
Figure 1 New Dimension Style Dialog Box
In engineering drawing, the commonly used dimensioning styles are set according to GB national mechanical drawing standards, and the height of engineering words is generally 3.5 and 5. Two linear dimensioning styles can be set, and the word height is 3.5 and 5 respectively based on the national standard IS0-25. After setting the following dimension styles, you can use DesignCenter to drag the set dimension styles to the required drawing.
1 linear dimension
The linear dimensioning style is set according to GB national mechanical drawing standard. The Line tab is dimension line, the baseline spacing is 5.25, the dimension line exceeds dimension line 1.75, the starting point offset is 0.875, the arrow size of the Symbols and Arrows tab is set to 3.5, the center size of the Center Mark is 3.5, the text height of the Text option is 3.5 or 5, and the text position is offset from dimension line by 0.875. In the Adjustment line, the adjustment option is set to text or arrow, the optimization is set to manual text placement, the decimal separator of linear dimensions on the Primary Units tab is set to period, and the Tolerance tab is set to none. Generally speaking, linear dimension, alignment dimension, arc length dimension and coordinate dimension all use linear dimension style. The following dimension styles are based on linear dimension styles. Recreate the dimension style, but only need to modify some settings.
2 Diameter size
In the engineering drawing, the diameter can be marked in various forms, as shown in Figure 2. Users should set different circle labeling styles or alternative labeling styles as needed. In the New (or Modified) Dimension Style dialog box, you can select the options in the Adjustment Options column of the Adjustment tab and the Optimization column of the Adjustment tab, the center mark in the Symbols and Arrows tab and the Text Alignment column in the Text tab. For the first size in Figure 2, in Adjustment Options of Adjustment tab, if there is not enough space between extension lines to put text and arrows, first remove it from the extension lines and set it as text and arrows. In the adjustment card, the optimization setting is to cancel drawing dimension line between extension lines, and the text tab is set to horizontal. For the second and third dimension styles in Figure 2, in the adjustment tab, the adjustment option is set to arrow, and the "Optimize" option in the adjustment card is set to draw dimension line between extension lines and manually place text, and the text is set to align with dimension line. In the fourth-dimensional style in Figure 2, the adjustment tab is the same as the second one, and the text alignment option in the text tab is set to horizontal. The adjustment option of the fifth adjustment tab in Figure 2 is set to text, and other options are consistent with the second option.
Figure 2 Diameter dimension style
3 Radius dimensioning
In engineering drawing, radius can be marked in various forms. Figure 3 generally sets the styles of four radius markers by adjusting the settings of tabs, text tabs and symbol arrow tabs.
Figure 3 Radius dimension style
4 Non-circular dimensioning
When other views corresponding to a circle are represented by straight lines, they are marked with the straight line marking command, but the marked size has no diameter φ. Set the non-circular dimension style separately, and enter %%c in the prefix of the primary unit option, so that you don't need to enter φ every time, just use the straight line dimension command. The period of the decimal separator option.
5 tolerance marking
Set tolerance labeling styles, and select tolerances in labeling styles, including symmetry, limit deviation, limit size and basic size. Symmetry deviation and limit deviation are often used, one each.
5. 1 Symmetric tolerance
Symmetrical deviation labeling style, the tolerance option is symmetrical, and the symmetrical tolerance value is entered in the upper deviation, with an accuracy of 0.00 and a height ratio of1; In some versions, the font name of the text option must be txt.shx, and no large font is used, otherwise the text is garbled.
5.2 Limit deviation
For the label style with extreme deviation, enter the upper deviation value in the upper deviation and the lower deviation value in the lower deviation. The upper deviation is positive and the lower deviation is negative. On the contrary, according to algebraic principles, negative numbers are positive numbers. The lower deviation value is negative, the input is positive, the lower deviation value is positive and the input is negative. When the tolerance dimension is marked for many times, it will be marked directly after setting. If the tolerance value changes, open the object properties, select the tolerance to be modified, and modify it within the tolerance value range in the object properties.
Hexagonal mark
The mechanical engineering drawing specifies the setting of angle dimension style, which requires the angle text to be horizontal, so the text alignment option on the text tab is set to horizontal.
7 Suppress dimensioning
Restrict the setting of dimension style. When the symmetrical revolving body figure is only half drawn, select the non-circular size, select the hidden dimension line 2 in the dimension line of the line option, select the hidden dimension line 2 of the extension line, and select the arrow 2 in the Symbols and Arrows tab as None.
8 plotted dimensions except 1: 1
Generally, the true scale of drawing a graph is 1: 1, but it is not 1: 1. There are three annotation methods besides 1: 1.
8. 1 Zoom graphics mode
When the drawing is output by scaling the drawing, the size will be marked after the scaling command is executed. And the size and style used need to be revised. In the dialog box for modifying the dimension style, enter the appropriate scale factor in the Measure Unit Scale option of the Main Units tab. If you use the zoom command to reduce the drawing by 50 times, you should enter 50 in the scale factor edit box of the measurement unit scale option. Adding text comments to a drawing is usually done after scaling the drawing. Just use the required text height value directly.
8.2 Output in proportion when printing
If the output is not printed at the scale of 1: 1 after the drawing is finished and the dimensions and text are marked, on the Adjust tab of the Modify Label Style dialog box, use the Global Scale radio button in the Label Element Scale option and enter the corresponding scale factor in the edit box on the right. If you want to print the output of 1: 100, you can print it.
8.3 Use layout
Draw a graph in model space according to 1: 1. When the drawn graph needs to be printed, switch to the graph space. Dimensions are marked in paper space. In the Modify Dimension Style dialog box, adjust the tab, select the radio option "Scale dimensions according to layout (drawing)" in the Dimension Feature Scale option, and mark in the floating viewport where the drawing to be marked is located.
conclusion
When designing products to draw graphics, a variety of reasonable dimensioning styles are set in advance, and the appropriate dimensioning styles are selected according to the actual needs, which greatly saves the dimensioning work time and improves the drawing efficiency, and has received very good results in the drawing work.
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