Laying Out an Internal Radius

Internal radius or corner radius is displayed in diagram at corner E. The laying out internal radius by divider is pretty tedious work because it is essential to position the point of the divider on the edge of the work-piece. A block of metal or wood held in opposition to the edge of the work will make the job much easier. If the work-piece is of steel or cast iron, a magnet positioned on the edge will work well.

(1) Clean the edge of the work-piece and eliminate all burrs.

(2) Mark off the position of the center of the internal radius of 8 cm (centimeter) from the corner.

(3) Set the divider to 2 cm (centimeter).

(4) Place the magnet on the edge of the work-piece at the marked position. Or, hold the flat metal or wooden block against the edge of the work at this point.

(5) Place the point of the divider on the mark and in the small groove among the magnet and the work.

(6) Scribe a semicircle, do not permit the point of the divider to slip out of the position.

(7) Mark this arc through the prick punch.