FreeCAD Sketcher: Line mid point

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FreeCAD is notoriously difficult to use - both for users completely new to CAD as well as users experienced with existing, commercially available CAD solutions. Throughout my years I worked with many different CAD 3D construction solutions such as Autodesk’s Inventor, Autodesk’s Fusion, Solidwork, OpenSCAD and several others. I always kept an eye on FreeCAD in the hopes of it becoming a viable alternative at some point. However, achieving even the simplest things are unintuitive and badly documented - if at all. The goal of this series is to document simple “How to do X” things in FreeCAD.

To add a constraint to the midpoint (middle) of a line segment we’re going to use the "Create symmetric constraint"-Tool which can be accessed for example through the toolbar. Keep a look out for the icon that looks like two arrows pointing at each other’s (chevrons for all your army aficionados). It looks like this:

FreeCAD symmetric constraint tool icon

Steps:

  1. Select the tree points in order:
    1. Line A point 1
    2. Line A point 2
    3. Line B point 1
  2. Click the "Create symmetric constraint"-Tool

FreeCAD being FreeCAD you can also do the reverse:

  1. Select the "Create symmetric constraint"-Tool
  2. Click on point 1 of line A
  3. Click on point 2 of line A
  4. Click on point a of line B

Example

Here is a full step-by-step example which demonstrates how to put a circle on the center line of a rectangle with a specific offset to one side in the Sketcher. The expected result looks like this:

Example Result

We start off with a simple rectangle:

Step 1

Next, add draw a line without paying any attention to where the points are located. Just place them randomly while ensuring that you do not create a constrain while doing so (e.g. don’t place the line’s points somewhere on the rectangle, the origin or anything else that allows “snapping”). Due to the nature of line I switched to the construction mode for the center line, but this is of course not necessary:

Step 2

Now were going to center the line. The process for both sides of the line is identical. We do this by:

  1. Clicking on the top left point of the rectangle
  2. Clicking on the bottom left point of the rectangle
  3. Clicking on the left point of the arbitrarily placed line
  4. Click on the "Create symmetric constraint"-Tool

After applying the same process to the second point of the new center line you should end up with the desired result:

Step 3

Now you can make use of your constructed center line by for example placing a circle on it:

Step 4

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