TechDraw Section Examples

Introduction
The TechDraw workbench has made a big step forward regarding the generation of section views. To not overload the reference pages, this page's intention is to give examples and supply proper naming for the performed tasks.

I'm doing my best to find the correct terms, but since I'm not an English native speaker, it's your turn to fix my mistakes if you find one.

Sections
Sections are used to look inside an object to show details that are otherwise invisible or hard to recognize. Usually there are views in the drawing showing the object from at least 2 directions. If a section is provided its position and orientation is indicated with a section line in one of the views.

In FreeCAD it is not possible to directly draw a section line, FreeCAD relies on task panel inputs instead (see Simple section and Complex section).

Example object
This object has no use at all except to describe the different section representations.



Simple sections
The Insert Section View tool creates a simple section that uses a single plane to cut through an object. The tool requires a base view ( property) to position the section plane. The vertical axis of the section plane is always the normal of the base view and the horizontal axis of the section plane is parallel to the section line. Usually the section view is oriented with its horizontal axis also parallel to the section line. The angle between section line and the base view's horizontal axis is controlled by widgets in the area of the tool's task panel:



The combobox allows to set an arbitrary angle. The four buttons can be used to set predefined angles:

90° (up), 270° (down), 180° (left), 0° (right)

Horizontal section
Section A-A (section up)





Section B-B (section down)





Vertical section
Section C-C (section left)





Section D-D (section right)





Arbitrary section
Section E-E (section at an arbitrary angle)





By default the section plane goes through the center of gravity of the object. To get an offset section we need to change the values in the area.



Auxiliary view
FreeCAD lacks a tool to derive auxiliary views from a base view, but Insert Section View can also handle that:

Using Section E-E from above and changing the mentioned values to X = and Y =  the section no longer cuts the object and becomes an auxiliary view instead. Note: be careful when changing the values, large steps can crash FreeCAD!

The label was edited manually. The section line and one arrow have to be hidden in following steps since a single arrow is enough to properly define an auxiliary view.

Single Section
If there is only one section view in the drawing, and it is plain to see that the object is cut along a center line, the section line, including the arrows, and the view title may be omitted.



Internal section
A section view may be integrated into the base view. This case doesn't require arrows and a title either.



Complex sections
The Insert Complex Section tool creates a complex section, such as an aligned section or an offset section, that uses more than one plane to cut an object.

The tool requires a base view ( property) to place several connected section planes to cut through the object, these are defined by a 3D polyline. (This tool can also handle curves, but curved sections are rather unusual.)

The vertical axes of the section planes are always parallel to the normal of the base view. Their horizontal axes are derived from the related segments of the 3D polyline. The orientation of the Section view depends on one of the 3D polyline's segments and is influenced by the widgets in the area of the tool's task panel:



This tool provides 3 options in the combobox to handle the section line segments:
 * : only segments perpendicular to the view direction are displayed (default).
 * : all segments are displayed in true length.
 * : all segments are projected along the same view direction. Depending on the angle between a segment and the view direction the projection may be shorter than the cut area. Segments parallel to the view direction result in a single line.

Offset section
An offset section starts with a base view plus a 3D polyline, a sketch in this case.

The view direction angle must be set to a matching value to avoid unexpected results.



Aligned section
An aligned section also starts with a base view and 3D polyline.

The view direction angle can be set by and  for a coarse orientation. It has to be guessed and set to a nearly matching value or the result could be other than expected.



This his how a bad guess result looks like:



Auxiliary view
The TechDraw ComplexSection tool can, like the  Insert Section View tool, create auxiliary views from base views:

An auxiliary view also starts with a base view plus a single 3D line placed outside the object.

The label was edited manually. The view direction (direction of the arrows) has to be extracted from the 3D line manually and you have to find the matching "View Direction as Angle" value manually. The section line and one arrow have to be hidden in followig steps since one single arrow is enough to properly define an auxiliary view.
 * There is a lot to do by hand, but it is a working solution, at least.

NoParallel section
A NoParallel section is a mixture of aligned and offset sections.

The arrow direction should have been horizontal, but in this case the tool did not work when the value of "View Direction as Angle" was set to. And so the sketch was rotated by 5° and said angle was set to, too.

Comparison NoParallel vs. Offset and Aligned


To be honest, if the value of "View Direction as Angle" of the aligned section was set to 5° exactly the result is faulty. When a section is activated for editing, said value is set to odd 5,14°, and it is confirmed with the check button then the expected result will be displayed.



Complex one line sections
One aspect that hasn't been focused on is that the length (width) of the section depends on the arrow positions i.e. the section line length. In contrast to simple sections where we have no influence on the section line length, we can control this length through the length of the used 3D line, but the results differ from Offset section to NoParallel section:



Half section
A view showing a symmetric object cut on one side of a center line and uncut on the other. The depth is usually defined by another center line.