Perpendicular Constructions

Section 1What perpendicular means

Perpendicular lines meet at a right angle, which is 90 degrees. In technical drawing, perpendiculars help create square corners, centre lines, and accurate layouts. Watch out: nearly 90 degrees is not good enough in construction work.

Section 2At the end of a line

To construct a perpendicular at the end of a given line, start from the endpoint and use compass arcs to create a right angle. Depending on the class method, you may use arcs that build from a 60 degree construction or a standard perpendicular construction. Here's the trick: keep the endpoint as the exact place where the new line starts.

Section 3At a point on a line

To construct a perpendicular to a given point on a line, mark equal distances on both sides of the point using a compass. From those marks, draw crossing arcs above or below the line. Join the given point to the arc crossing to form the perpendicular.

Section 4Checking accuracy

Use light arcs and a sharp pencil. Check that the perpendicular passes through the required point and forms 90 degrees. A school workshop drawing for a shelf bracket needs this accuracy so the parts fit properly.