TechDraw General Examples

Introduction
The TechDraw workbench is quite stuffed with tools related to technical drawings, but what are the required elements to turn a piece of paper into a proper drawing? This page is intended to give some explanation and some examples about what TechDraw is already capable to do.

Drawings
A drawing consist of one or more views to describe a part geometrically... But you know that already, don't you?

Let's have a look at the basic elements.

Sheet of paper
Paper sizes are standardised and to be able to print without scaling the format of our virtual sheets should match with the desired printing format.

Frames
When drawings were drawn by hand the had to be pinned or taped to a horizontal table or a vertical drawing machine. Puncher holes were added to the finished drawing to attach the folded drawing to the file or folder. This outer area is separated by a rectangular framed another rectangular frame inside the first one defines the drawing area. There is usually a set of indexes and separators between both frames used to allocate certain drawing elements.

Title block
The title block contains written information about the part and the drawing such as part number, title, author, owner, etc.

Bill of material
Optionally assembly drawings can have a bill of material (BOM) included.The BOM can also be placed on a separate drawing sheet or a spreadsheet.

Change log
Changes to part or drawing are protocolled in a log on the drawing or in a separate document and linked to the drawing by corresponding indexes.

Views
Views contain the geometrical description of a part from a certain direction. Most parts need at least two views to be properly described.

Annotations
Additional texts that don't belong to the elements above.

Drawings made with TechDraw
Techdraw uses a Page object as a container for all drawing related elements; this cannot exist on its own, but has to contain a template. That is why there is no New page command and a new page object is created automatically whenever a template is inserted.

Templates
A Template object is an SVG image file and its code holds all information needed to create a virtual sheet of paper with matching frames and title block, and optionally a BOM.

Since svg images are not parametric a template has to be exchanged whenever the format, the frame layout, or a title block element has to be modified. That means for each format a separate template has to be created, such a set of templates is needed for any variation of frame or title block objects. That is quite a lot to code and manage but on the other hand templates cannot change accidentally inside FreeCAD.

There are several ways to create a template:
 * 1) Draw it with Inkscape, see How to create a custom TechDraw template.
 * 2) Type it manually, see Template explained.
 * 3) Use a macro, see TechDraw TemplateGenerator and Macro TemplateHelper.





The drawing so far
Up to this point it is safe to say that TechDraw in connection with embedded SVG templates can provide a proper drawing sheet with frame and title block. Some entries can be altered after creation thanks to editable texts, and some content can be inserted automatically if macros are involved.

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Views
The views contain the geometrical 2D description of an object. The content of a TechDraw view can be derived from 3D geometry or obtained from another workbench like Arch Views and  Draft views.

Since FreeCAD is a 3D modelling application TechDraw's key function is deriving 2D views from 3D geometry. Let's have a look at an easy example, the part from the Basic Part Design Tutorial that is also used with the Basic TechDraw Tutorial:



Active View
An Active View is more or less a screen shot of the 3D view in its own kind of TechDraw view.



View
A View is TechDraw's  basic view object to derive proper drawings. In contrast to an Active view it is not restricted to visible objects on the screen, but also displays selected objects outside the screen. The preferred scale is usually 1:1, but it is finally depending on available space or the level of detail that has to be displayed.



Projection Goup
A Projection Group is a set of views. Each view direction is perpendicular to its neighbour and all depend on the 3D window's direction by default. TechDraw provides six views matching with the Navigation Cube sides, and four isometric views.



Section View
TechDraw provides two tools to create a Simple Section View or a  Complex Section View. Both depend on a base view and on tools to define a section line and to derive the view direction. Have a look at TechDraw Section Examples for an overview.



Auxiliary View
If we need a view of the tilted plane to see its true lengths we would define the view direction in a base view and place the Auxiliary view accordingly, but TechDraw provides no tool for Auxiliary views yet.

Good news: It is quite easy to emulate using the Simple Section View tool:


 * 1) Select a base view.
 * 2) Create a [[Image:TechDraw_SectionView.svg|16px]] Simple Section View with default settings.
 * 3) Use [[Image:TechDraw_AngleDimension.svg|16px]] Insert Angle Dimension to measure the angle of the plane.
 * 4) Edit the section view angle in the Set View Direction area of its task dialog.
 * 5) Edit the section view coordinates in the Section Plane Location area of its task dialog. Use small steps to move the section line outside the object or FreeCAD may crash.
 * 6) Hide unwanted annotation elements such as section line, section arrows, and section name.
 * 7) Add needed items like view arrow, and view name.







Detail View
A Detail View is a copy of an area of a base view usually to magnify hardly visible geometry.



Imperfections

 * Detail views according to ISO standard do not have a frame/ border (the upper part of the enclosing circle)
 * The break line that cuts the detail off the rest should be a thin freehand line or the cad equivalent, a thin zig-zag line.
 * FreeCAD/TechDraw do not provide freehand/zig-zag lines at all (yet).
 * Hatched areas in the base view should be hatched in the detail view, too.

Arch View
A TechDraw Arch Views displays a view of an  Arch SectionPlane. Its content is rendered by the Arch workbench.

Draft View
A TechDraw Draft view displays a view of a selected Part-based or Group object. Its content is rendered by the Draft workbench.



Spreadsheet View
A Spreadsheet View displays a view of a Spreadsheet Workbench sheet.



The views so far
TechDraw needs some additions like break lines, and a proper auxiliary view tool and also some improvement of the Detail view tool. But even in this state we can describe our objects visually quite well:



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Dimensioning
Now that our item is described geometrically, dimensions will be added to further define the teoretical shape, and tolerances to define the allowed deviation. TechDraw supplies several tools to apply dimensions to the 2D representation of our item:
 * [[Image:TechDraw_LengthDimension.svg|16px]] Length Dimension
 * [[Image:TechDraw_HorizontalDimension.svg|16px]] Horizontal Dimension
 * [[Image:TechDraw_VerticalDimension.svg|16px]] Vertical Dimension
 * [[Image:TechDraw_RadiusDimension.svg|16px]] Radius Dimension
 * [[Image:TechDraw_DiameterDimension.svg|16px]] Diameter Dimension
 * [[Image:TechDraw_AngleDimension.svg|16px]] Angle Dimension
 * [[Image:TechDraw_3PtAngleDimension.svg|16px]] 3-Point Angle Dimension

The have in common that they measure the projected shape of the item. If you you have learnt drafting the manual way, you know how to use auxiliary views to turn the item into a position where projected lengths equal the true lengths. For visualisation other than this old school way the dimensions can be linked with the 3D geometry using TechDraw LinkDimension and display "true dimensions".

Another two tool measure the overall length horizontally or vertically respectively: These cannot be linked with 3D geometry (yet).
 * [[Image:TechDraw_HorizontalExtentDimension.svg|16px]] Insert Horizontal Extent Dimension
 * [[Image:TechDraw_VerticalExtentDimension.svg|16px]] Insert Vertical Extent Dimension

See Dimension dialog (and the following properties section) for all settings that are not mentioned in this overview.

Simple dimensions
The dimension text depends mainly on these specifiers:
 * By default these specifiers' defaults are
 * By default these specifiers' defaults are
 * By default these specifiers' defaults are
 * By default these specifiers' defaults are

To "cheat" we use this two specifiers:
 * Set to to use the content of the Format Spec to format the actual dimensional value.
 * Set to to use the content of the Format Spec to be displayed as text instead if the dimension value.
 * Set to to use the content of the Format Spec to be displayed as text instead if the dimension value.


 * : Like, but for the tolerance.

If we only need the dimension value there's nothing to do but to change the number of decimals if desired.
 * For example: →  to display 3 decimals, or  →  to display whole numbers.

Tolerances
Tolerances express how much a measured dimension may deviate from the dimension value on the drawing. To suffix a tolerance values to the dimension value simply set the property to a value other than, this results in a symmetric tolerance such as.

For an asymmetric tolerance set property to  and specify also a lower value for the  property.

The values can be set in the Dimension dialog or directly in the Property editor.

Hole/shaft fit
Fit tolerances (tolerance classes) can be suffixed in three ways:
 * 1) Set the  property to  and specify both tolerance classes (letter + number codes) to the  and  properties.
 * 2) Use the [[Image:TechDraw_HoleShaftFit.svg|16px]] Add hole or shaft fit tool. This suffixes only one tolerance class but adds the related values to the  and  properties.
 * 3) For a single tolerance simply suffix the tolerance class to the format specifier of the  property

Thread fit
Thread fit tolerances (tolerance classes) have the number before the letter and can be suffixed like described above for hole/shaft fit tolerance classes, except method 2.

Geometric dimensioning and tolerancing
Datums

Datum feature

Datum target

Theoretically exact dimensions

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Annotations
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