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Dimensioning & Tolerances

Created: April 12, 2022 | Updated: May 19, 2022 | Applies to version: 22
Now reading version 20.0. For the latest, read: Dimensioning & Tolerances for version 25
 

Parent page: Streamlining Board Design Documentation with Draftsman

Dimensions

Object dimension graphics may be placed on Board Views (Assembly, Fabrication, Section, Details, etc.)  to indicate the lengths, sizes, and angles of the object outlines, or the distance between nominated objects. To place a dimension graphic, select the desired type from the Place menu or from the Dimension drop-down on the Active Bar.

The dimension tools are available on the Active Bar, click and briefly hold the dimension button to open the menu.
The dimension tools are available on the Active Bar, click and briefly hold the dimension button to open the menu.

Measurement units:

Note that the units system (Metric or Imperial) that applies to a Draftsman document is defined by the Units settings in the Properties panel when in Document Options mode. However, for individual objects such as Linear/Radial Dimensions, Drill/BOM Tables and the Layer Stack Legend, their default units may be preset to Imperial or Metric in the Draftsman – Defaults page of the Preferences dialog. These settings will override the document's base Units setting when a new object of that type is placed.

In turn, the Units used by the placed object can be locally changed through the Units option in the Draftsman Properties panel, when the object is selected.

What objects can a Dimension be attached to?

Each of the Draftsman View types extracts and presents the data that best suits the function of that View. For example, a Board Assembly View is often heavily annotated with dimensions, notes and details about specific components. In an Assembly View the important element for a mounting hole is the drill size and hole center point, not the size of the copper donut that might be present around the hole, or the soldermask expansion value.

From the extracted data, Draftsman makes the following points available as references for dimensions in a Board Assembly View: the centerline and end points of lines and arcs; the edges and edge end points of polygonal shapes; and the center points of circles (holes) and arcs.

The Board Fabrication View is used to show how the copper presents on each fabricated layer. Different data is extracted from the PCB for this type of View, now the copper donut around the mounting hole is more important than the size of the drill hole. This View offers the following points for dimensioning: the centerline and end points of lines and arcs; the edges and edge end points of polygonal shapes; the center of circular shapes (pads, vias and arcs), but not the center of rectangular pad shapes. If a pad has routing to its center then the end point of that routing line will be available, regardless of the pad shape.

If dimensions created in a Draftsman document are snapped to a primitive that is removed from the PCB document, the dimension objects themselves are not removed and will remain greyed-out on the Draftsman document.

Why Can't I Dimension that Curve?

Polygonal shapes that include curved edges in their design are actually rendered in the PCB editor with the curves replaced by short, straight segments (zoom in close in the PCB editor to see this). This applies to polygons, regions and the board shape. That means if your board shape includes a curved edge, that edge cannot be used to draw a radial dimension in Draftsman, because there is no curved object present.

However, arcs are rendered as a curved object with a radius, so they can be used to draw a radial dimension in Draftsman. If your board has a curved edge that needs to be dimensioned, include a board outline on a mechanical layer in the PCB editor. This outline can be created directly from the board shape if it does not exist. Then enable that mechanical layer in the Draftsman View to be able to add a radial dimension to the curved edge.

The curve in a board outline is created from short straight segments, include an outline on a mechanical layer to dimension the curve. Hover the cursor over the image to reveal the outline.
The curve in a board outline is created from short straight segments, include an outline on a mechanical layer to dimension the curve. Hover the cursor over the image to reveal the outline.

Linear Dimension

A Draftsman Linear Dimension is an automated dimensioning object that can be placed between the vertices or edges of Draftsman objects, including Board Views and component objects. This allows a dimension to be placed on the side of an object, between two points on an object, or between nominated sides/vertices of two different objects.

The visual style of the dimension lines and the configuration of the dimension text data can be set in the Properties panel when a placed Linear Dimension is selected.

A variety of Linear Dimensions applied to a Board Assembly View.
A variety of Linear Dimensions applied to a Board Assembly View.

To place a Linear Dimension, select Place » Linear Dimension from the main menu or the  icon from the Active Bar dropdown. When the command is launched, the cursor will change to a crosshair, indicating Linear Dimension placement mode. As the cursor is hovered over objects, the object edges and vertex points will be highlighted as orange-colored lines and dots, respectively.

To dimension an object edge (side) the placement steps are:

  1. Click on a highlighted object edge to place the dimension reference point.
  2. Move the mouse and click to set the position of the dimension text and its associated extension lines.

To place a dimension between two object edges or vertices, the placement steps are:

  1. Click on a highlighted object edge or vertex point to place the dimension's first reference point.
  2. Click on another highlighted object edge/vertex to place the dimension's second reference point.
  3. Move the mouse and click to set the position of the dimension text and its associated extension lines.

To cancel the placement mode, press Esc or right-click in the design space.

The Linear Dimension can be graphically modified by selecting any part of its graphic representation and dragging the dimension text to a new X/Y location – its associated extension lines will adjust accordingly.

Select and drag the dimension text to a new position.
Select and drag the dimension text to a new position.

An existing reference point in a placed Linear Dimension can be moved to a new location through a drag and drop action. When moved, the reference node binds to the new vertex/edge/center and causes the Linear Dimension data (the displayed measurement) to update accordingly, as shown in this animated demonstration.

Radial Dimension

A Draftsman Radial Dimension is an automated dimensioning graphic that applies to a circular board object (hole) or an arc on a Board Assembly View or a Board Fabrication View, or an associated graphic such as a Board Detail View. The text of the placed Radial Dimension reports the radius of the object.

The visual style of the dimension lines and the configuration of the dimension text data can be set in the Properties panel when a placed Radial Dimension is selected.

A variety of Radial Dimensions applied to a Board Assembly View.
A variety of Radial Dimensions applied to a Board Assembly View.

To place a Radial Dimension, select Place » Radial Dimension from the main menu or the  icon from the Active Bar dropdown. When the command is launched, the cursor will change to a crosshair, indicating Radial Dimension placement mode. To dimension a hole, object the placement steps are:

  1. Hover the cursor over circular hole objects in a Board Assembly View. Each hole perimeter will be highlighted as an orange-colored outline.
  2. Click on a highlighted hole outline to place the dimension target reference.
  3. Move the mouse and click to set the position of the dimension text and its associated pointer line.

To cancel the placement mode, press Esc or right-click in the design space.

The Radial Dimension can be graphically modified by selecting any part of its graphic representation and then dragging its editing handle new location; its associated extension lines will adjust accordingly.

Select and drag the dimension's editing handle to a new position.
Select and drag the dimension's editing handle to a new position.

Diametral Dimension

The Diametral Dimension is an automated dimensioning graphic that applies to circular hole objects in a Board Assembly View. The visual style of the dimension lines and the configuration of the dimension text data can be set in the Properties panel when a placed Diametral Dimension is selected. The Diametral Dimension can be graphically modified by selecting any part of its graphic representation and then dragging its editing handle to the new location; its associated extension lines will adjust accordingly. The visual style of the dimension lines and the configuration of the dimension text data can be set in the Properties panel, when a placed Diametral Dimension is selected.

A variety of Diametral Dimensions applied to a Board Assembly View.
A variety of Diametral Dimensions applied to a Board Assembly View.

To place a Diametral Dimension object, select Place » Diametral Dimension from the main menu or the  icon from the Active Bar dimension dropdown. When the command is launched, the cursor will change to a crosshair, indicating Diametral Dimension placement mode. To dimension a hole object the placement steps are:

  1. Hover the cursor over circular hole objects in a Assembly View. Each hole perimeter will be highlighted as an orange colored outline.
  2. Click on a highlighted hole outline to place the dimension target reference.
  3. Move the mouse and click to set the position of the dimension text and its associated pointer line.

To cancel the placement mode, press Esc or right-click in the design space.

The size, and therefore, number of holes that will be included in a Board Assembly View is determined by the Display Holes setting and its associated Minimum Diameter field in the Assembly View Properties – see the panel's Properties section.

Use the Diametral Dimension tool to show the diameter of a hole in an Assembly View.
Use the Diametral Dimension tool to show the diameter of a hole in an Assembly View.

Angular Dimension

A Draftsman Angular Dimension is an automated dimensioning graphic that reports the relative angle between two object faces (or a Center Mark crosshair line) on a Board Assembly View or a Board Fabrication View, or an associated view such as a Board Detail View. The automated dimensioning graphic reports the relative angle between two object faces, such as the sides/edges of a component or board. The dimension graphic style and its text content can be set to a range formats in the Properties panel when a placed Angular Dimension is selected.

A variety of Angular Dimensions applied to a Board Assembly View.
A variety of Angular Dimensions applied to a Board Assembly View.

To place an Angular Dimension, select Place » Angular Dimension from the main menu or the  icon from the Active Bar dropdown. When the command is launched, the cursor will change to a crosshair indicating Angular Dimension placement mode. To dimension the angle between two object faces, the placement steps are:

  1. Hover the cursor over an object face edge (or Center Mark crosshair line) and then click the highlighted line to select the first angle reference.
  2. Hover the cursor over another object edge/line and then click the highlighted line to select the second angle reference.
  3. Move the mouse then click to set the position of the dimension text and the style of the angular dimension lines (see Graphical Editing below).

To cancel the placement mode, press Esc or right-click in the design space.

The Angular Dimension can be graphically modified by selecting any part of its graphic representation and then dragging its editing handle to a new location. During the repositioning (and during initial placement of the dimension) the arrowed dimension lines will automatically adjust their drawing mode and/or add extension lines to best match the current text position.

Select and drag the dimension's editing handle to a new position.
Select and drag the dimension's editing handle to a new position.

Ordinate Dimension

A Draftsman Ordinate Dimension is an automated dimensioning object that is composed of multiple linear dimension elements that are relative to a specified reference point. The dimensions in the ordinate set can be placed on the outlines edges or vertices of Draftsman objects in a Board Assembly View (or its Section View), including the board itself. The indicated dimensions are effectively cumulative as they are placed at increasing distances from the nominated reference point, and can be placed on the outlines edges or vertices of a placed board view or its constituent objects.

The visual style of the dimension lines and the configuration of the dimension text can be set in the Properties panel when a placed Ordinate Dimension is selected.

A variety of Ordinate Dimensions applied to a Board Assembly View. A variety of Ordinate Dimensions applied to a Board Assembly View.

To place an Ordinate Dimension set, select Place » Ordinate Dimension from the main menu or the  icon from the Active Bar dropdown. When the command is launched, the cursor will change to a crosshair, indicating Ordinate Dimension placement mode. As the cursor is hovered over objects, the object edges and vertex points will be highlighted as orange-colored lines and dots, respectively.

The Ordinate Dimension placement steps are:

  1. Hover the cursor over the drawing view until the desired (reference) point or object edge is highlighted.
  2. Click to select this as the dimension reference point then move the cursor and click to set the extension position and angle.
  3. Continue selecting points to create the full series of dimensions that are relative to the first placed reference point.

To cancel the placement mode, press Esc or right-click in the design space. Dimensions can be added or removed from the ordinate set after it has been placed – see Graphical Editing below.

A series of Ordinate Dimensions are treated as one object, but individual entries can be added and removed.
A series of Ordinate Dimensions are treated as one object, but individual entries can be added and removed.

When a set of Ordinate Dimensions has been selected in the design space, by clicking on any part of its graphic representation, it can be graphically modified in the following ways:

  • Drag the dimension's lines or text to a new location on the same axis. In this editing mode, the set of dimensions behave as one object and can be moved as a single entity.
  • To add a new dimension to the ordinate set, select another highlighted object location on the drawing view.
  • To remove an individual dimension from the ordinate set, click on its node handle.

Select and drag the dimension set to a new position, or add/remove individual dimensions.Select and drag the dimension set to a new position, or add/remove individual dimensions.

The set of dimensions behave as one object, and can, therefore, be moved as a single entity or edited as an object in the Draftsman Properties panel. However, note that individual dimensions may be added or removed when the Ordinate Dimension object is selected.

X,Y Axis Scale

The X,Y Axis Scale object can be used to place a reference scale against any type of View object. Various properties of the object can be customized, including the thickness, stylistic design of the line styles, and font choice. The visual style of the axis scale and the configuration of the axis scale text data can be set in the Properties panel when a placed X, Y Axis Scale is selected.

A variety of X, Y Axis Scale applied to a Board Assembly View.
A variety of X, Y Axis Scale applied to a Board Assembly View.

To place an X,Y Axis Scale, select Place » X,Y Axis Scale from the main menu or select the  icon from the Active Bar dimension dropdown. Hover the cursor over the required object in the View and the cursor will change to an orange dot, indicating a valid reference point. Click to attach the zero end of the scale. Reposition the cursor and click a second time to attach the far end of the scale; then move the cursor to set the distance between the referenced objects and the Axis Scale, click a third time to place the scale.

The X, Y Axis Scale object can be graphically modified by selecting any part of its graphic representation and then dragging its editing handle towards or away from the Board Assembly View object – its associated extension lines will adjust accordingly.

Select and drag the dimension's editing handle to a new position.
Select and drag the dimension's editing handle to a new position.

Geometric Dimensioning and Tolerances

Draftsman includes the capability to place and configure industry-standard Geometric Dimensioning and Geometric Tolerances symbolic elements that define the manufacturing properties of objects included in a drawing.

Also used in most advanced MCAD applications, the specialized information provided by the placed geometric symbols stipulates the allowable imperfections in the manufacture of physical objects.  The geometric definition elements that can be added to Draftsman documents are derived from standards developed by the American Society of Mechanical Engineers (ASME) – specifically, the ASME Y14.5-2009 Dimension and Tolerancing standard. Many other standards and guidelines exist for geometric engineering definitions, including a large number of conceptually specific documents from the International Organization for Standardization (ISO).

► See Geometric dimensioning and tolerancing for overview information and reference links.

In terms of Draftsman engineering documents, the symbol-based Dimensioning and Tolerancing information is incorporated into a drawing by the placement of two types of objects:

  • Datum Feature symbols – Identification objects that can be attached to a line, point or axis of a physical feature in a drawing, such as the edge of the board, component or hole.
  • Feature Control Frames – Information objects that can be attached to a drawing feature, which include multiples of symbolic data that specify the mechanical manufacturing constraints for the feature.

Both of the above drawing objects can be positioned freely in the document, or (normally) attached to a feature such as an edge. In the same way in which other Drawing Annotations are placed in Draftsman, such as Surface Finish symbols, the geometric definition symbols are attached by clicking on a highlighted line in the drawing and then clicking again to place the symbol.

Datum Feature

A Datum Feature is a graphic identification object that can be attached to a line, point, or axis of a physical feature in a drawing, such as the edge of board, component, or hole. It acts as a reference on that drawing object so that relative dimension tolerances included in Feature Control Frames can refer to this and other placed datum. When added to the mechanical elements in a Draftsman drawing view, the combined information represented by Feature Control Frames and their related Datum references can fully describe the acceptable manufacturing constraints for those physical elements.

A number of Datum Feature symbols attached to the surface edges of objects in a Board Assembly View.
A number of Datum Feature symbols attached to the surface edges of objects in a Board Assembly View.

Place a Datum Feature on a drawing using the Place » Datum Feature menu command or by selecting the icon from the Annotations drop-down on the Active Bar. After launching the command, the cursor will change to a cross-hair and the editor will enter Datum placement mode. Placement is made by performing the following actions:

  1. Position the cursor over a highlighted object edge then click to attach the Datum Feature to that object face.
  2. Move the cursor to set the position of the Datum label then click again to complete placement.

The graphical method of editing allows a placed Datum object to be selected in the design space and its edge attachment point or label location changed. When a Datum Feature object is selected, editing handles/nodes become available at its attachment and header label points.

A selected Datum Feature with its two positioning nodes
A selected Datum Feature with its two positioning nodes

  • Click and drag the label node to reposition it on the drawing document.
  • Click and drag the edge attachment node to reposition it along the selected object face. An extension line is added when the attachment point is moved beyond the boundary of the object face.

The Datum Feature is identified by its Label entry in the Properties panel so that relative dimension tolerances included in Feature Control Frames can refer to this and other placed datum.

Feature Control Frame

A Feature Control Frame is a graphic information object that can be placed on a Draftsman document sheet to define the manufacturing constraints of the physical feature to which it is attached, such as an object face or machined cutout/hole.

The tabular frame object applies a specialized range of symbols, tolerance values and location references to specify acceptable manufacturing imperfections as defined by the ASME Y14.5-2009 Dimension and Tolerancing standard. Draftsman Datum Feature objects are used as reference locations in placed Feature Control Frames. Attached machining tolerances, such as the 'straightness' of a feature for example, apply to the specified drawing object face. Attached Dimension tolerances by comparison (such as 'position') are generally specified as relative to one or more placed Datum. When added to the mechanical elements in a Draftsman drawing view, the combined information represented by Feature Control Frames and their related Datum references can fully describe the acceptable manufacturing constraints for those physical elements. See Applied Geometric Tolerances for information on a number of basic examples.

The graphic style and dimensioning/tolerancing attributes for a placed Feature Control Frame are definable in the Properties panel. Multiple definition rows may be added to the frame in the Selected Element region of the Properties panel.

Feature Control Frame objects attached to a hole and an edge in a Board Assembly View. The three Datum Feature objects are used as reference locations.
Feature Control Frame objects attached to a hole and an edge in a Board Assembly View. The three Datum Feature objects are used as reference locations.

Place a Feature Control Frame on a drawing using the Place » Feature Control Frame menu command or by selecting the icon from the Annotations drop down on the Active Bar, and attach it to a drawing feature as outlined above, or place it free space. After launching the command, the cursor will change to a cross-hair and the editor will enter Feature Control Frame placement mode. Placement is made by performing the following actions:

  1. Position the cursor at the required point within the drawing; typically this will be a feature such as an edge. In this case, position at a point where the drawing element is highlighted (an edge or a point). With the cursor in position, click to attach the feature control frame to that feature.
  2. Move the cursor to set the position of the frame then click again to complete placement.

The graphical method of editing allows a placed Feature Control Frame to be selected in the design space and its object attachment point or frame location changed. When the Feature Control Frame object is selected, editing handles/nodes become available at its attachment and frame points.

A selected Feature Control Frame with its two positioning nodes.
A selected Feature Control Frame with its two positioning nodes.

  • Click and drag the tabular frame to reposition it on the drawing document.
  • Click and drag the edge attachment node to reposition it on the selected object face. An extension line is added when the attachment point is moved beyond the boundary of the object face.

The information it conveys, presented in symbols, modifiers and numeric values, is entered in the Properties panel.

Applied Geometric Tolerances

When added to the mechanical elements in a Draftsman drawing view, the combined information represented by Feature Control Frames and their related Datum references can fully describe the acceptable manufacturing constraints for that physical element.

In the example drawing view shown below, dimensions have been added, Datum Feature references attached to the three visible board edges, and Feature Control Frames applied to the top edge and two mounting holes. The Feature Control Frames have multiple elements added, which appear as a sequence of (selectable) rows – note the Add, Delete etc., buttons in the Selected Element area of the Properties panel.

The symbols and formatting used in the various Feature Control Frames are fully described in the ASME standard, however, an overview of the examples shown above is as follows:

  • Frame attached to edge A
    • First element (top row) – stipulates the flatness tolerance (acceptable deviation in the surface) for the board edge.
    • Second element – stipulates parallel tolerance (acceptable distance, and therefore angle deviance) between sides A and C.
  • Frame attached to Hole X
    • First element (top row) – stipulates the hole position tolerance (acceptable positional error) relative to both Datum A and Datum B.
    • Second element – stipulates the roundness tolerance (acceptable diameter variance) for the hole.
  • Frame attached to Hole Y: A Composite Feature Control Frame (as selected by the related checkbox in the Properties panel)
    • Symbol for this frame (first column) – defines this Frame as positional information, for all elements (rows).
      • First sub element – stipulates the tolerance (acceptable error) for Hole Y relative to Datum B.
      • Second sub element – stipulates the tolerance (acceptable error) for Hole Y relative to Datum C.
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