QCAD 3.2 has been released this week with four new circle tools:
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Circle tangential to an entity and through two points. |  |
Circle tangential to two entities and through a point. |
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Circle tangential to two entities with given radius. |  |
Circle tangential to three entities. |
Perhaps surprisingly, most of these solutions are not at all straight-forward to find without the use of a CAD system. The problem to create circles that are tangential to three given circles, lines or points is sometimes referred to as the 'Problem of Apollonius' and has been solved by various mathematicians over the centuries.
Depending on the exact geometry of the tangential entities, there can be multiple (not always obvious) solutions to the problem. QCAD lets you pick the desired solution in the final step of the appropriate tool.
In the example at the right, the three dark blue circles were chosen as tangential circles. QCAD previews all eight possible solutions so that the desired solution can be chosen by simply clicking next to it. In this example, the innermost circle is chosen, shown in green.
I hope these tools will further boost your productivity!
Andrew