How to use a marking knife

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You can use a marking knife freehand for small cuts (for example, when marking dovetail joints) or use a guide such as a straightedge, engineer’s square or try square for longer cuts. The instructions that follow tell you how to use a marking knife with an engineer’s square or try square.

Tools you will need: 

• A marking knife (either a single-bevel or double-bevel)

• An engineer’s square or try square

• A pencil or some chalk (optional)

• Workpiece

When using a marking knife, the bevel side of the blade always faces away from the workpiece – the flat back of the blade always rests against the guide. This applies to both double-bevel and single-bevel marking knives. However, when scribing with a single-bevel marking knife there’s a restriction on the direction in which you can score.

For example, if you are marking the pins of a dovetail joint you will be using the outline of the tails for your guide. When marking a dovetail joint you will need a left-hand single-bevel knife to go along the left side of the tails, and a right hand single-bevel to go along the right side. 

A double-bevel marking knife can be used to mark each side of the guide.

Step 1 – Hold marking knife

Hold the marking knife in your dominant hand, similar to the way you would hold a pencil. If the handle of your marking knife has an indent, place your thumb and fingers in it.

Step 2 – Place 

Position the blade of the marking knife on the workpiece, with the tip of the blade at the beginning of the line you want to cut.

Step 3 – Position straightedge

Slide the straight edged tool (square) into position so that the side of it touches the flat back of the knife. Make sure the square is correctly positioned, so the handle is square against the edge of your workpiece.

Step 4 – Make cuts

Firmly hold the square with your non-dominant hand and drag the blade of the knife across the surface of your workpiece. Make sure you drag the blade slowly so you keep to the straightedge and produce an accurate cut. A single cut should be enough, but for a more visible line make three or four light passes.

If you are planning to extend the lines around the corner and part-way down the side of the workpiece, for example when making a dado (groove) for a housing joint, place the marking knife at the edge of the workpiece and rotate the blade 90 degrees gently around the wood’s corner to extend the groove. The same applies when you want to cut right through the workpiece, but the mark would need to go all the way down the side. 

Step 5 – Highlight scribed lines (optional)

If the cut is hard to see, use a finely sharpened pencil or some chalk to highlight the line. The pencil can be used on lighter coloured woods while chalk or a white pencil is better for dark coloured woods.