The knife wall

Sometimes you come across a new-to-you technique and suddenly the floor is soaking wet – an eureka! moment worthy of Arkimedes just happened. Are you sick and tired of tearout? Come here, my friend…

The first time I heard of this technique, I realized the importance straight away. Every man, woman and child that has tried to cut a piece of wood knows about tearout. It does not matter how sharp your saw is either, how expensive your table-, miter-, track-, circular- or jigsaw is or what moon phase it is at the time. Unsupported wood fibres on the exit side WILL tear out. For oak just as well as the softest pine – maybe even worse so.

I heard about the knife wall from Paul sellers. Here is one video he made on the subject.

But since I have you here (and because I reference this technique a lot), I’ll show you.

1. Establish the line. You measure the length and mark it with the tip of your marking knife. Press the knife into the wood a little so that you get a positive mark. If your knife slips out of that mark, it is easy to place it back. Slide your square up to the knife, registering on one of your reference faces. Score the line along the square. First a light pass, then several passes gradually harder and harder. Make sure you cut the edges of the piece hard. This will transfer your line to the other side.

2. Transfer your line. Slide your knife along the corner until it “snaps” down into that nick you made. Slide the square up to the knife and repeat the marking process. If your piece is “four square”, or 4S (meaning that all sides are square and parallell), you should be able to transfer your line around the piece perfectly. If something is off, register off of the same two reference faces for three of the four faces. The last face can’t be done with a square if something is out, but you can use the ruler if you want to – connect the marks on each corner. I’d just leave that out in such cases.

If you do not want to mark all faces, for example if you want to mark for a through mortise, just lightly nick the corners with the knife. It will work great, and the nick will be removed if you smooth the edges.

3. Make a channel. Remove a wedge on the waste side with a chisel. The idea is to make a trough for the saw, so we want to make it deep enough. Angle in towards the knife wall you scribed. The waste should pop out easily, leaving a crisp, perfect wall. If you cut lower than the knife line, the waste won’t pop out. Just wipe “against the grain” and it’ll break off easily. Any remains can be removed with the knife (deepen the wall), a chisel or just be left behind as long as it does not obstruct the saw.

4. Rinse and repeat for the other faces. You do not need to do this on all four sides. The top and the exit side will be sufficient, but if you are going to plane the end grain it will benefit you to do all four. I also find that I get cleaner results when the saw “breaks through” on the underside, but that could just be me.

4. Saw. Whether you are cutting to length, cutting tenon shoulders or what have you,keep close to the knife wall but do not cut into it. If your sawyer genes aren’t fully developed, stay away from the wall and we’ll finesse it later. This article on saw technique might help you here.

5. Be proud! If you examine the piece on the left, you can clearly see the knife wall on the upper left corner.

Let’s zoom in from space and read the registration plate:

I’ve drawn two lines to mark the knife wall. Look at the upper right corner – that’s a sharp edge right there!

As you can see, I cut pretty close to the knife wall. A few swipes with a hand plane, and I cleared that right up. You can also use a chisel to to this; you register the edge on the knife wall and pare inwards from all sides in a snake-esque wiggling motion, slicing the fibres as you go.

The ends on the seat slats on this bench I made, shows how nice the end grain will look after the fact. All the slats were cut to length and cleaned up like I have described. The piece of gash used for the example images above actually came from one of these slats:

– And remember: you can do this for miters as well. Any angle! Done diligently, you will get perfect results every time.

The knife wall is such a simple thing, but it has a tremendous impact on our work. Even if you use machines for all your cuts, a knife wall will eliminate tearout and ensure a perfect cut every time. No need for sacrificial boards on your fences. Make the knife wall and register a tooth on your table saw blade against the wall and set your fence. Done.

Or leave a gnat’s nadger of material which you clean off with a hand plane and perhaps a shooting board. It will improve the surface quality a lot.

Hand tool techniques does not suit the use of power tool? How blue-eyed can you be? Hopefully not as much as that lord Coldemort or what’s-his-name…

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