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How to use an engineer’s square?

How to use an engineer’s square

Shop for Engineer’s Squares

Other equipment you may need:

Marking tools, pencil, engineers scriber, marking knife

Marking tool

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.

A light can be used behind an engineer's square and the workpiece to help highlight any gaps between the two that indicate the workpiece isn't square

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.

Engineers' marking ink is used to aid the contrast of scribed lines on metal workpieces

Engineer’s marking ink

Engineer’s marking ink is used on metal workpieces to help make the contrast of the scribed line stand out.

Wonkee Donkee says: "If you are marking out a metal workpiece, it is a good idea to use an engineer's scriber and marking ink to ensure that the layout lines are as clear as possible."

Begin work

Marking out ink should be applied to metal workpieces and left a few minutes to dry before marking

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.

When holding an engineer's square on a workpiece you wish to mark out, Use your thumb and index finger to hold the blade down onto the workpiece surface. Use your other fingers to pull the stock up to the edge of the workpiece.

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.

Using a marking knife to mark a line down the outside of an engineer's square blade

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.

The outside of an engineer's square can be used to check a workpiece is square by butting the square up to the workpiece and checking for light shining between the two.

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.

The inside of an engineer's square can be used to check a workpiece is suare

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.

If no light is visible then the workpiece is square 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.

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