TechDraw Geometric dimensioning and tolerancing
Overview
The main purpose of a technical drawing is that others understand what the designer created with what tolerances and material and how to manufacture the design. To achieve this the system of Geometric Dimensioning and Tolerancing (GD&T) was developed for defining and communicating engineering tolerances.
TechDraws' capabilities to fulfill the common GD&T standards is limited (as of FreeCAD 0.19) but you can achieve already many things. This Wiki page explaisn what is implemented and what tricks can be used for non-implemented features.
Dimensioning
TechDraw provides several tools to create different types of dimension. Please have a look at the different dimensions on how to create and modify them.
Formatting
The default format for new dimension numbers depends on the preferences options Use Global Decimals and Alternate Decimals. This specifies the number of decimals, but in every case the dimension is a floating point number. For example if the setting is to have 2 decimals, the used format specifier is "%.2f" (floating point number with 2 decimals).
The number format can be changed:
- Select a dimension in the tree
- Go to the properties tab Data and there to the section Format
- The property DataFormat Spec contains the format specifier, so change it to what you need
The syntax of the format specifier is explained here. You can also use this online tool to see what formatting specifier will format numbers.
Examples:
- You use 2 decimals but for an angle you want to have only one decimal use the format specifier %.1f.
- You use 2 decimals but don't like that trailing zeroes are printed (you prefer 4 instead of 4.00). Then use this format specifier: %g. The 'g' will use the shortest possible output and thus it omits trailing zeroes. Moreover it will automatically switch to scientific notation if necessary.
With the property DataInverted you can make length dimensions negative and flip angles from the range 0 - 180° to the the reflex range 180° - 360°.
Setting the property DataTheoretical Exact to true will mark the dimension as theoretically exact by adding a frame around it.
You can use your own text instead of a formatted number by setting the property DataArbitrary to true. Then the content of the property DataFormat Spec will be printed as dimension.
With the properties DataX and DataY you can change the horizontal and vertical position of the dimension text relative to the view. Alternatively you can change the position by dragging the dimension number or text.
Tolerancing
TechDraw only supports dimensional tolerancing. Geometrical tolerancing is however possible with tricks.
Dimensional
Creation
- Create a dimension in your drawing
- Select the dimension in the tree
- Go to the properties tab Data and there to the section Format
- Add to the property DataOver Tolerance the amount by which the dimension can be exceeded.
- Add to the property DataUnder Tolerance the amount by which the dimension can be smaller.
Deletion
To get rid of a tolerance, change the the properties DataOver Tolerance and DataUnder Tolerance to each 0.00.
Formatting
The default format for new tolerances is by default the same format than the dimension (property DataFormat Spec). It can be changed by changing the properties DataFormat Spec Over Tolerance and DataFormat Spec Under Tolerance.
You can also use your own text instead of a formatted number by setting the property DataArbitrary Tolerances to true. Then the content of the properties DataFormat Spec Over Tolerance and DataFormat Spec Under Tolerance will be printed as tolerances.
Tolerances appear by default like this: . However, in many cases you have equal over- and undertolerance, thus it should better be displayed like "7,87 ±0,1 mm" since this is the standard. The only way to achieve this at the moment, is to delete the tolerances as described in the section above. Then set DataArbitrary to true an enter the the dimension as it should appear: "7,87 ±0,1 mm".
Geometric
Concept
The concept of the geometrical tolerancing is that in practice the dimension is just one parameter to decide if a part can he used or not. Take for example this part:
In the application an axis should be put through the 2 holes of the part. That mean we have to specify the following things
- The diameter of the holes and they are equal.
- That the holes are along a certain axis that is not perpendicular to the XY base plane.
- That the axis part must have a certain straightness.
The straightness is important because a bend axis would not fit through the holes. Thus it has to be specified for the axis part and not to our part. The hole alignment is important because just drilling each hole at the given position without taking care of the axis, would lead to holes through which the axis won't fit. So just specifying the hole dimension and position is not sufficient.
- Pages: Insert Default Page, Insert Page using Template, Redraw Page, Print All Pages
- Views: Insert View, Insert Active View, Insert Projection Group, Insert Section View, Insert Complex Section View, Insert Detail View, Insert Draft Workbench Object, Insert Arch Workbench Object, Insert Spreadsheet View, Insert Clip Group, Share View, Project Shape
- Stacking: Move view to top of stack, Move view to bottom of stack, Move view up one level, Move view down one level
- Decorations: Hatch Face using Image File, Apply Geometric Hatch to Face, Insert SVG Symbol, Insert Bitmap Image, Turn View Frames On/Off
- Dimensions: Insert Length Dimension, Insert Horizontal Dimension, Insert Vertical Dimension, Insert Radius Dimension, Insert Diameter Dimension, Insert Angle Dimension, Insert 3-Point Angle Dimension, Insert Horizontal Extent Dimension, Insert Vertical Extent Dimension, Link Dimension to 3D Geometry, Insert Balloon Annotation, Insert Axonometric Length Dimension, Insert Landmark Dimension, Adjust Geometric References of Dimension
- Annotations: Insert Annotation, Add Leaderline to View, Insert Rich Text Annotation, Add Cosmetic Vertex, Add Midpoint Vertices, Add Quadrant Vertices, Add Centerline to Faces, Add Centerline between 2 Lines, Add Centerline between 2 Points, Add Cosmetic Line Through 2 points, Add Cosmetic Circle, Change Appearance of Lines, Show/Hide Invisible Edges, Add Welding Information to Leader, Add Surface Finish Symbol, Add Hole or Shaft Tolerances
- Extensions:
- Attributes and modifications: Select Line Attributes, Cascade Spacing and Delta Distance, Change Line Attributes, Extend Line, Shorten Line, Lock/Unlock View, Position Section View, Position Horizontal Chain Dimensions, Position Vertical Chain Dimensions, Position Oblique Chain Dimensions, Cascade Horizontal Dimensions, Cascade Vertical Dimensions, Cascade Oblique Dimensions, Calculate the area of selected faces, Calculate the arc length of selected edges, Customize format label
- Centerlines and threading: Add Circle Centerlines, Add Bolt Circle Centerlines, Add Cosmetic Thread Hole Side View, Add Cosmetic Thread Hole Bottom View, Add Cosmetic Thread Bolt Side View, Add Cosmetic Thread Bolt Bottom View, Add Cosmetic Intersection Vertex(es), Add an offset vertex, Add Cosmetic Circle, Add Cosmetic Arc, Add Cosmetic Circle 3 Points, Add Cosmetic Parallel Line, Add Cosmetic Perpendicular Line
- Dimensions: Create Horizontal Chain Dimensions, Create Vertical Chain Dimensions, Create Oblique Chain Dimensions, Create Horizontal Coordinate Dimensions, Create Vertical Coordinate Dimensions, Create Oblique Coordinate Dimensions, Create Horizontal Chamfer Dimension, Create Vertical Chamfer Dimension, Create Arc Length Dimension, Insert '⌀' Prefix, Insert '〼' Prefix, Remove Prefix, Increase Decimal Places, Decrease Decimal Places
- Export: Export Page as SVG, Export Page as DXF
- Additional: Line Groups, Templates, Hatching, Geometric dimensioning and tolerancing, Preferences
- Getting started
- Installation: Download, Windows, Linux, Mac, Additional components, Docker, AppImage, Ubuntu Snap
- Basics: About FreeCAD, Interface, Mouse navigation, Selection methods, Object name, Preferences, Workbenches, Document structure, Properties, Help FreeCAD, Donate
- Help: Tutorials, Video tutorials
- Workbenches: Std Base, Assembly, BIM, CAM, Draft, FEM, Inspection, Mesh, OpenSCAD, Part, PartDesign, Points, Reverse Engineering, Robot, Sketcher, Spreadsheet, Surface, TechDraw, Test Framework
- Hubs: User hub, Power users hub, Developer hub