You will need a marking tool such as a marking knife, engineer’s scriber, or pencil to mark lines at a right angle across the surface of the workpiece.
Light
You may need a light to shine behind the workpiece and engineer’s square to help highlight any gaps between the edges of the square and the workpiece.
Engineer’s marking ink
Engineer’s marking ink is used on metal workpieces to help make the contrast of the scribed line stand out.
Begin work
Step 1 – Apply marking ink
Apply the marking ink in a thin, even layer to metal workpieces and leave a few minutes to dry before you begin marking out.
Step 2 – Position square up against edge of workpiece
To mark a line at a right angle to the edge of a workpiece, you should hold the stock of the engineer’s square up against the edge of the workpiece, and the blade flat on the surface. Do this with your less dominant hand by placing your thumb and index finger on the blade on the engineer’s square, then use your other fingers to pull the stock tight up to the edge.
Step 3 – Mark line
Once your engineer’s square is held securely against the edge of the workpiece (with your less dominant hand), take your marking tool (pencil, engineer’s scriber or marking knife) in your dominant hand and mark a line down the outside edge of the blade, beginning at the stock-end of the engineer’s square.
Step 4 – Check internal angles
You can use the outside edges of an engineer’s square to check that the internal angles between the surfaces of a workpiece are square. Do this by butting the outside edges of your engineer’s square up against the workpiece and looking to see if any light shines between the outside edges of the square and the inner edges of the workpiece. If no light is visible, then the workpiece is square.
You may find that placing a light behind the workpiece and square makes this easier.
Step 5 – Check external squareness
The inside of an engineer’s square can also be used to check the external squareness of a workpiece. To do this, butt the stock of the square up to the edge of the workpiece with the inside edge of the blade sitting across the workpiece surface.
Look down the workpiece to check if any light is showing between the inner edges of the engineer’s square and the workpiece. If no light is visible, then the workpiece is square.
You may find that placing a light behind the workpiece and square makes this easier.