Lines tangent to arcs

There are 3 different ways of creating a line tangent to an arc. These are:

• creating a line with the start position already defined.
• creating a line with start position as a tangent point on the arc.
• creating a line between two arcs.

If you want to create a line tangent to an arc when its start position is already defined, its second position is defined by clicking the arc. The arc is automatically trimmed to where the line is tangent with it.

The position at which you select the arc is important, because it decides:

• where the tangent solution is.
• which portion of the arc to trim.

To create a line tangent to an arc:

1. Click Wireframe tab > Create panel > Line > Single or Continuous.
2. Input positions to create your lines and where you want a line tangent to an arc, select the arc instead of entering a position.

For example, suppose you have a start position of a line and an arc as shown below:

In this case, the line is tangent to two positions on the arc .

Select the arc at a position nearest to the required tangent.

Note: The arc has three key points (its end points and midpoint) which are used to snap on to. If you select a key point on the arc, the end of the line is positioned there and no tangency position is found. To find a tangency point on an arc, hold the cursor over the arc until the word 'Tangent' appears.

If you require the top tangent, the arc is selected in a position (apart from the arcs key points) shown below:

The selection positions lie on either side of the position where the line falls tangent to the arc. Which side of the arc is selected determines how the arc is trimmed. If the arc is selected to the left, it is trimmed as shown below:

If the arc is selected to the right, it is trimmed as shown below:

You can click the arc first and then input the end position of the line. The tangent on the arc is determined in the same way in both cases.

You can also create a line which is tangent to two arcs. A line tangent to both arcs is given in the figure below:

Note: For a full arc (circle), its start and end points move to coincide at the position where the line is tangent to it.

If the tangent position lies off the arc, then the nearest end point of the arc to the tangent position extends to this position.

The line and arc must lie in the same plane.