The video “Marking Knives Don’t Prevent Joinery Gaps, But DOING THIS Will” is by Inspire Woodcraft. In this informative piece, Jodee shares insights into achieving tight joinery without gaps, a common challenge faced by woodworkers.

Many woodworkers have been led to believe that a marking knife is essential for tight joinery, and that using a pencil is a no-go. Jodee points out that while a marking knife is a fantastic tool for layout, it doesn’t necessarily prevent gaps in joints. In fact, even with a well-tuned marking knife, gaps can still occur. But why does this happen? Let’s dive into the details.
The Experiment
To illustrate the point, Jodee conducts a simple experiment using a piece of Ash and a piece of Walnut. The goal is to create a joint similar to a half lap, without actually making a complete half lap. Instead of using a marking knife, a standard carpenter’s pencil is employed. By coloring both sides of the Walnut, a sort of knife point or chisel point is created, though not as precise as a marking knife.
After making the marks and cutting the material, the Walnut is fitted into the Ash. Surprisingly, the joint turns out to be quite tight with only a tiny gap, which could have been caused by slight movement during the cutting process. This raises the question: how can a joint be so tight using just a carpenter’s pencil?
Understanding the Knife Edge
Jodee explains that while the pencil marks are wider than those made by a marking knife, the critical aspect is where the point of the mark lands. By creating a knife edge through the pencil’s use on scrap wood, the point is directed into the corner of the joint, ensuring that the material is removed from the middle, resulting in a snug fit.
However, the use of a marking knife introduces a different challenge. With a marking knife, there are usually one or two bevels. The flat side goes down into the material while the beveled side creates a V-shaped cut. This V shape can lead to gaps if not managed properly. If the V shape is on the side where the material is removed, it can create a misalignment, resulting in visible gaps.
Scoring Techniques
To avoid this issue, Jodee recommends using a light scoring technique. Instead of making deep, dark cuts that create a pronounced V shape, a light pass should be made to create a hairline score mark. This technique allows for precision without creating the gap issues associated with deeper cuts.
When making cuts, positioning the knife with the bevel side against the waste side can help maintain accuracy. Jodee emphasizes that once you have your light lines, you can proceed to cut the material out, ensuring that the knife line is on the waste side, which will prevent any gaps in the final joint.
Final Thoughts
In summary, while marking knives are excellent tools, they are not a guaranteed solution to prevent gaps in joinery. Understanding the mechanics of how marking knives work and employing the correct scoring techniques can lead to tight, gap-free joints. Woodworkers are encouraged to experiment with both marking knives and pencils to see what works best for their specific projects.