21. Ovals

Smooth convex curves, outlined by arcs of circles of different radii, are called ovals. Ovals consist of two bearing circles with internal mates between them.

There are three-center and multi-center ovals. When drawing many details, such as cams, flanges, caps and others, they outline the contours of the ovals. Consider an example of constructing an oval along given axes. Let for a four-center oval, delineated by two supporting arcs of radius R and two mating arcs of radius r , are given the major axis AB and the minor axis CD. The magnitude of the radii R ur must be determined by building (Fig. 36). Connect the ends of the major and minor axes with the segment A С, on which we will set aside the difference CE of the major and minor semiaxes of the oval. Perpendicular to the middle of the segment AF, which intersects the major and minor axes of the oval at the points O ₁ and O ₂ . These points will be the centers of the conjugating arcs of the oval, and the conjugation point will lie on the perpendicular itself.

Fig. 36