DIMENSIONS IN AUTOCAD
A technical drawing is incomplete without annotation. Notes on a drawing are important to convey design information or clarify intent which can’t be portrayed by linework alone. Measuring distances from a scaled, printed drawing is inaccurate. Dimensions allow exact values to be shown on a drawing which can then be used for construction.
You can access the dimensioning tools from the Ribbon Annotate tab > Dimension panel. The required dimension tool can be chosen from the Dimension drop-down.
The Linear dimension tool measures horizontal or vertical distances. To create Linear dimensions click the points 1, then 2 to identify the element to be dimensioned. Click point 3 to locate the dimension line. The dimension distance will show the vertical or horizontal distance depending on whether you move your cursor in a horizontal or vertical direction when placing point 3.
Command line: To start the Linear Dimension tool from the command line, type “DIMLIN” and press [Enter].
The Aligned dimension tool measures the length along an object.
To create an Aligned dimension click the points 1, then 2 to identify the element to be dimensioned. Click point 3 to locate the dimension line.
Command line: To start the Aligned Dimension tool from the command line, type “DIMALI” and press [Enter].
The Angular dimension tool measures an angle between two objects.
To create an Angular dimension select object 1, and then object 2 to identify the elements creating the angle. Click point 3 to locate the dimension line.
Command line: To start the Angular Dimension tool from the command line, type “DIMANG” and press [Enter].
The Arc Length dimension tool measures the length of an arc.
To create an Arc Length dimension, select object 1 then click point 2 to place the dimension line.
Command line: To start the Arc Length Dimension tool from the command line, type “DIMARC” and press [Enter].
The Radius dimension tool measures the radius of an arc or circle.
To create a Radius dimension, select object 1 then, click point 2 to locate the dimension line.
Command line: To start the Radius Dimension tool from the command line, type “DIMRAD” and press [Enter].
The Diameter dimension tool measures the diameter of an arc or circle.
To create a Diameter dimension, click object 1 then, click point 2 to locate the dimension line.
Command line: To start the Diameter Dimension tool from the command line, type “DIMDIA” and press [Enter].
The Jogged dimension tool measures the radius of an arc or circle but places the leader line in an alternative place (inferred point) to the arc or circles centre point. The jog indicates the dimension line doesn’t point to the centre of the circle. This tool can be used when space is limited or the arc radius is large.
To create a Jogged dimension, click on the arc you want to dimension (point 1). Click point 2 to identify the inferred centre point. Click point 3 to locate the dimension line and text. Click point 4 to locate the jog within the dimension line.
Command line: To start the Jogged Dimension tool from the command line, type “JOG” and press [Enter].
Ordinate dimensions are used to locate the X or Y coordinate value of a point. Click point 1 to identify the point location, click point 2 to locate the dimension line. Ordinate dimensions are especially useful for elevations or OS grids which use specific coordinates.
Note: The ordinate dimension will display the X value if your second point is above or below the first point. The Y value will be displayed if your second point is to the side of the first point.
Command line: To start the Ordinate Dimension tool from the command line, type “DIMORD” and press [Enter].
The Quick Dimension tool is used for dimensioning multiple elements.
Quick Dimensions can be added by clicking the Quick Dimension tool from the Ribbon Annotate tab > Dimensions panel.
Command line: To start the Quick Dimension tool from the command line, type “QDIM” and press [Enter].
Select all the objects you wish to dimension (objects 1). You can either select these 1 at a time or use a crossing window selection to select multiple objects.
Click point 2 to locate the dimension line.
The Continue dimension tool is used to add additional dimensions to a linear, aligned Angular or Arc length dimension.
Continue only works on an existing Linear or Aligned dimension. It takes the settings and height from the existing dimension chosen.
Note: The direction is based on the extension line clicked. If you select the right side extension line it will start to measure from the right side, if you select the left side extension line, it will measure from the left side.
You can create a Continue dimension by clicking the Continue tool from the Ribbon Annotate tab > Dimensions panel..
Command line: To start the Continue Dimension tool from the command line, type “DIMCONT” and press [Enter].
A Continue dimension is created by selecting the already created Linear or Aligned dimension (1) then by clicking the subsequent points (2, 3 and 4).
Baseline dimensions will measure the distance from a starting point to multiple other points.
Baseline only works on an existing Linear or Aligned dimension. It takes the settings and height from the existing dimension chosen.
Note: The direction is based on the extension line you click. If you select the right extension line it will measure from the right side, if you select the left extension line, it will measure from the left side.
You can create a Baseline dimension by clicking the Baseline tool from the Ribbon Annotate tab > Dimensions panel.
Command line: To start the Baseline Dimension tool from the command line, type “DIMBASE” and press [Enter].
A Baseline dimension is created by selecting the already created Linear or Aligned dimension (1) then by clicking the subsequent points (2, 3 and 4).
The Multileader dimension tool creates arrows and text pointing to objects.
To create Multileaders click the Ribbon Annotate tab > Leaders panel > Multileader button.
Command line: To start the Multi Leader tool from the command line, type “MLD” and press [Enter].
Click point 1 to locate the start of your Multileader. Click point 2 to locate the end of your Multileader. 3 enter the text you wish to display.
To add additional Leaders to your Multileader click the Add Leader button from the Ribbon Annotate tab > Leaders panel.
Click an existing Multileader (1) to identify what you want to add a Leader to. Click point 2 to identify the location of the arrow of the additional Leader line.
When placing dimensions, by default, they are created Associative. An Associative Dimension will automatically adjust if the geometry it dimensions is modified.
Dimension associativity is controlled from the AutoCAD Options. To show the AutoCAD options, right click the command line and choose options.
The options dialog box will show. The dimension associativity feature can be found on the User Preferences tab by ticking and un-ticking the Make new dimensions associative tickbox.
When this option is ticked (the default setting), Dimensions will be associated to objects. If the object is modified, the dimension will adjust to match. This is the preferred method of dimensioning because it keeps the correct dimension value when geometry is edited.
If unticked, the dimension is not associated to any objects. If the geometry is later adjusted, the dimension will remain in its original location and will need to be modified manually.
The appearance of individual dimensions can be altered using the properties palette but using styles will ensure consistency.
To view the Dimension Style Manager dialog box, click the Dimension Style button from the Ribbon Annotate tab > Dimensions panel.
Command line: To open the Dimension Style Manager from the command line, type “DDIM” and press [Enter].
The available styles will be listed in the Styles section of the Dimension Style Manager dialog box.
Sub-styles will show linked to a Style. Sub-styles are used where different properties for a specific dimension tool are required e.g. a different arrow head for Leaders than the other dimensions in the parent Style.
Creating Dimension Styles
New dimension styles are created by clicking the New button. The Create New Dimension Style dialog box will show allowing you to enter a New Style Name for your dimension style. You have to choose an existing dimension style as a starting point.
Once the new style has been created, the New Dimension Style dialog will show with all the properties of the starting dimension style.
The tabs across the top of the dialog box control the different aspects of the dimensions.
The dimension below shows which tab is used to modify each part of the dimension.
The Lines tab controls the appearance of the dimension and extension lines.
The image shows the extension lines and dimension lines
Color controls the colour of the Dimension lines or Extension lines
Linetype controls the linetype of the Dimension lines. There are two linetype options in the Extension lines section: Linetype ext line 1 and Linetype ext line 2, where the 1 is the first extension line placed.
Lineweight controls the lineweight of the Dimension lines or Extension lines.
Baseline Spacing is the space between the text and the dimension line.
Supress Dim Line / Ext Line allows you to remove the dimension or extension lines so they are not shown. This can be useful when placing dimension or extension lines over other geometry such as grid lines so the dimension doesn’t obscure the dimension line.
Extend beyond dim lines is the distance the Extension lines extend above and past the Dimension lines
Offset from origin is the distance from the object being dimensioned to the start of the Extension lines.
Fixed length extension lines is the length of dimension lines can be fixed to help keep the appearance of dimensions tidy. To change the dimension line length, on the Lines tab, tick the Fixed length extension lines option and enter a length for your dimension lines in the Length box. Each new dimension will now have extension lines fixed to the length you specified in the Length box.
Symbols and Arrows
The Symbols and Arrows tab controls the arrow heads at the end of the Dimension lines and Centre marks.
Arrowheads controls the arrow head type and size of the arrowheads on the end of dimension lines.
Center marks controls the appearance when marking centre points of circles and arcs. It is quite often important to use centre marks to set out a curved element.
Dimension Break is the size of the break mark when using Jogged dimensions.
Arc Length Symbol controls the location of the arc length dimension symbol. In the example, the symbol is shown Proceeding dimension text.
Radius jog dimension controls the jog angle on Jogged dimensions.
Linear jog dimension controls the jog height factor as a ratio of the text size for jogged dimensions.
The text tab controls the appearance of text. This shouldn’t be confused with the Primary and Secondary Units tabs which control the value of the text.
Text appearance controls the style of text used, the colour and the height. (For more details on Text and Text Styles, see module 06-Text)
Text Placement controls the location of the text in relation to the Dimension line.
Note: The JIS (Japanese Industry Standard) placement isn’t shown but is the same as the Above option.
View direction Controls whether the text is read from left to right or right to left.
Text Alignment controls the rotation of the text: whether it is rotated to the view orientation, whether it aligns with the dimension being created, or whether it follows ISO standard (which maintains all text horizontally).
The fit options control how the text in a dimension reacts when space is limited and the overall scale of the text.
Fit options controls how the text and arrows relocate around the extension line if there isn’t enough space. When dimensioning smaller objects, AutoCAD will relocate the text, arrows or both depending on the selected option.
Text Placement controls where the text is located when it is reposition by the Fit options.
Scale for dimension features controls dimension scale in one of two ways: the manual method and the annotative method.
On the Fit tab of the Modify Dimension dialog box, enter the scale of your drawing e.g. if your drawing will be scaled 1:100, enter a value of “100” in the Use overall scale of box. This will scale the dimension attributes such as text and arrows by 100.
On the Fit tab of the Modify Dimension dialog box, tick the Annotative option to use the file’s Annotation Scale to scale your dimensions.
Annotative Dimension Styles are based on the Annotation Scale. Select your Annotation Scale as required from the Drafting Settings at the bottom of your application window.
If the Add Scales button is active, annotative objects will change size when the Annotation Scale drop-down value is changed. The selected Annotation Scale will be assigned to the annotation.
When Annotation Visibility is activated the annotation will re-size to display at the current Annotation Scale, if that scale is assigned to the object. If the select Annotation Scale has not been assigned, the annotation will remain at its current size. For example, if an annotative dimension is only assigned to 1:50 and the Annotation Scale is changed to 1:100, the dimension will remain at 1:50.
When an annotative object is selected, the different scales the annotative object uses are displayed. In the diagram below, an annotative dimension is selected. Its text appears at 1:20 and 1:100 scales.
These are the units used by the dimensions.
Linear Dimensions is the unit format of distance dimensions. You can apply prefixes and suffixes to indicate the unit format being used. For example, if you are dimensioning in millimetres, you would enter a Suffix of “mm”.
Measurement scale is the scale that the dimension length will be multiplied by to give the final dimension value. When dimensioning an object drawn in metres in millimetres, entering a Scale factor of “1000” will give the correct result. i.e. if the object if 5m long, using a Dimension Style with a Scale factor of 1000 will result in a “5000” (5 x 1000) dimension value.
Zero Suppression removes leading and trailing zeros. If a measured value was 100.00, ticking the Trailing option would give a dimension of 100.
Angular Dimensions controls the unit format of angles.
You can display two different unit values on your dimensions, such as metres and feet, by ticking the Display alternate units option from the Alternate Units tab.
Set a scale factor from the original units. E.g. If you drew in mm and want to convert to inches, enter a scale factor of “0.03937” (this is 1 / 25.4, the scale factor to convert from mm to inches) in the Multiplier for alt units box.
Note: When using Alternate Units, it is recommended to add a suffix (e.g. in, mm) to help clarify which units are being used.
The Placement section controls the location of the Alternate Unit in comparison to the original units.
Moving Dimension Text
To move dimension text select the dimension to be modified to show the dimension’s Grips. Click the centre Grip over the text. Move the text to the required location.
The dimension line will also move to maintain the alignment between the text and the dimension line.
Editing Dimension Text
The value of the dimension text can be modified as required.
Note: It is not recommended to change the value. If you require a different value, the geometry should be amended. Editing dimension text should only be used to add suffixes, prefixes and if dimensioning “Not to scale” drawings.
To change the text, select the dimension to be modified. Right-click and choose Properties to show the Properties palette. From the Text Override field enter a new value to be displayed.
In the image below, note the difference between the Measurement (100), the actual dimension value, and the Text override (120 NTS). The dimension is actually 100 long, but has been edited to read “120 NTS”.
Using the <> symbols will display the dimension value.
For example, to change a dimension from “500” to “Width = 500”, enter the value:
“Width = <>”
To change the dimension value back to the default of just the value, delete any Text override value.
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