rebat

To rebat is to rotate an orthographic view out of its plane and into the plane of an adjacent view, using their line of intersection as the hinge. In technical drawing, this unfolds a three-dimensional relationship onto a single sheet so that true lengths and angles become visible and measurable. The term comes from the French word for a fold or flap, and the operation itself is also called a rebatment or a rabatment.

The most common use is in auxiliary views and developed surfaces. When a draughtsman needs to show the true length of a slanted edge, or the true shape of a surface that lies at an angle to the principal planes, rebatting swings that view into the plane of the front, top, or side elevation. A hole drilled through an angled surface must be drawn true size and shape, which requires rebatting the oblique plane into the projection plane. This is essential before calculating positions for drilling or milling operations.

Rebatting works only where two planes meet at a definite edge or line of intersection. The view rotates as if hinged along that edge until it lies flat in the drawing plane. Points in the rebatted view maintain their distances from the hinge line; coordinates measured perpendicular to the hinge remain unchanged. This geometric property makes rebatting exact and reversible: the true measurement in the rebatted view corresponds directly to the actual dimension on the part.

Modern CAD software performs rebatting computationally, but the principle remains unchanged. A draughtsman working by hand uses a compass and straightedge: arcs swung from the hinge line transfer distances from the original view into the rotated view. The rebatted geometry then becomes a construction that supports dimensioning, hole spacing, or pattern layout.

Rebatting is distinct from simple rotation or perspective sketching because it preserves orthographic projection. The view does not merely turn or tilt; it unfolds along a specific edge so that dimensions remain valid. Confusion between rebatting and pictorial projection often leads to incorrect hole locations or surface calculations, so the operation must be performed with care and verified against the line of intersection.