- Coordinates for 3D CAD Modeling
- Geometric Entities
- 4.1 Manually Bisecting a Line or Circular Arc
- 4.2 Drawing Tangents to Two Circles
- 4.3 Drawing an Arc Tangent to a Line or Arc and Through a Point
- 4.4 Bisecting an Angle
- 4.5 Drawing a Line through a Point and Parallel to a Line
- 4.6 Drawing a Triangle with Sides Given
- 4.7 Drawing a Right Triangle with Hypotenuse and One Side Given
- 4.8 Laying Out an Angle
- 4.9 Drawing an Equilateral Triangle
- 4.10 Polygons
- 4.11 Drawing a Regular Pentagon
- 4.12 Drawing a Hexagon
- 4.13 Ellipses
- 4.14 Spline Curves
- 4.15 Geometric Relationships
- 4.16 Solid Primitives
- 4.17 Recognizing Symmetry
- 4.18 Extruded Forms
- 4.19 Revolved Forms
- 4.20 Irregular Surfaces
- 4.21 User Coordinate Systems
- 4.22 Transformations
- Key Words
- Chapter Summary
- Skills Summary
- Review Questions
- Chapter Exercises

## 4.3 Drawing an Arc Tangent to a Line or Arc and Through a Point

Given line *AB*, point *P*, and radius *R* (Figure 4.25a), draw line *DE* parallel to the given line and distance *R* from it. From *P* draw an arc with radius *R*, cutting line *DE* at *C*, the center of the required tangent arc.

**4.25** Tangents. *These are often easy constructions using CAD and object snaps.*

Given line *AB*, with tangent point *Q* on the line and point *P* (Figure 4.25b), draw *PQ*, which will be a chord of the required arc. Draw perpendicular bisector *DE*, and at *Q* draw a line perpendicular to the line to intersect *DE* at *C*, the center of the required tangent arc.

Given an arc with center *Q*, point *P*, and radius *R* (Figure 4.25c), from *P*, draw an arc with radius *R.* From *Q*, draw an arc with radius equal to that of the given arc plus *R.* The intersection *C* of the arcs is the center of the required tangent arc.