What’s ‘Knifewall’?

It’s just a more active word when the two come together—less passive without a hyphenation. I like knifewall because it’s more punchy, but really I like it more because it so describes what I want people to see. It’s 20 or so years old now, not much more. It’s not that I invented its work, more that I defined the result of using it. Knifewall didn’t exist when I thought it up, started using it and then penned it, but it isn’t all that easy to come up with something you can actually name and then go ahead and name it. It was a knife cut and a crossgrain wall side by side. Why not bring them together? Unite them?

So there I was, looking at my knifewall and standing in front of 20 students when, right out of the blue, I just said it. ‘KNIFEWALL!’ I said it again and then again, to solidify it, you know, and, well, it just fit. I’d said the word knifewall for the very first time and it meant exactly what it said. It was made with a knife and the knife made the wall you see. So I coined it, the word ‘knifewall‘, in the absence of an accurate term, to take its rightful place in the vernacular of woodworkers. Cutting that knife line and sharing the new term with others meant something significant. I should perhaps have coupled it with another word I used at the same time, shoulderline, because 99% of the time the knifewall creates a shoulderline, which is the intersecting line creating that critical juncture between two pieces of wood.

I don’t know if any other craft develops such a physical wall this way, it doesn’t really matter. Knifewall says it just the way I said it and the way I wanted to say it and no other word or phrase exists that gives it such succinctness—certainly not make a knife mark’ or ‘strike a line‘; two terms I heard in school as a boy at thirteen—hence ‘marking knife’ and ‘striking knife’.

Here you can see how the grain crumples under the pressure on the softer grain aspect either side of the harder (dark) slow growth period of the growth ring when using a less than surgically sharp knife. That’s not to say that you can’t sharpen a marking/striking knife, but most often they were used as a blunt instrument!.

Back then they did give us “striking knives” with 6″ long points on, alongside pencils, to work with, but neither pencil nor striking knife gave us what we really needed; neither could give us the parting off we didn’t know we wanted. It’s also something that back then we may have feigned stabbing or lunging actions playfully but it never entered our psyche to actually injure someone. What changed?

The marking/striking knife as it was in the mid 1960s or so when it was last used in schools and in the industry. Pencils were well established and it was of course the pencil that saw the demise of the marking knife as the method for marking wood.

For my craft, woodworking of any and every kind, it’s wood that demands the definition because wood generally has unidirectional grain. The grain develops following the longitudinal aspect of the tree’s growth as it follows its up-reaching growth toward the light and warmth of the sun. Just as surely as the word apricity has value in describing this action of being warmed by the sun, though not used so much any more, the term knifewall describes cuts across the grain to prevent the wood’s surface fibres from ripping and tearing because it’s counter to the course of the tree’s grain. When other cutting-edge tools follow to advance deepening cuts  adjacent to the knifewall, the knifewall serves both as a guideline and a line for other tools like chisels, planes and saws to register to. Thus the knifewall becomes both the guideline and the wall that separates the waste from the wanted.

Notes and drawing from one of my journals of some time back.
Note: One thing that often takes a little while to understand and register surrounds the issue of bruising from the bevel of the knife: that this should be on the waste side of the wood, and therefore that the knife be held so that the bevel rides against the square in a deliberate perpendicular presentation. This then means leaning the knife slightly to one side. I think the close up photo at top shows this well enough, and helps cement this idea by seeing it from this angle. The result is shown below.
It’s important to see the knifewall not as symmetrical but asymmetric, which comes as something of a surprise. See how when the one knife bevel rides against the straightedge and is presented perpendicularly it creates a square-to-edge wall but on the other aspect to the opposite bevel it creates a more bruised or forced angle, which is evidenced by the compressed wood at the facing edge there.

In contrast, the knife mark was  relatively under-defining even though the square would be placed dead in the line or mark. Impressing a less than sharp knife onto the wood’s surface leads only to the knife scoring the surface rather than a severed knifewall. This then develops more a trough-like indenting and one incapable of severing the surface fibres as happens with only the very lightest pressure if the knife is truly sharp.

The fibres compressed thus along the line both to the side of the square and also beneath its beam, develops only a ‘vee’ channel and no true knifewall at all. For some work this would be adequate and permissable but to develop cut lines leading to perfectly closed shoulderlines it’s not enough. Woods with contrasting density surrounding growth rings, pine, fir or spruce for instance, leaves the line undulating as the wood compresses at differing levels across the width. I say this to avoid confusing knife mark with knife nick as the nick severs and the mark indents.

After many years of my using the knifewall, decades, I began teaching others the method the same way because it did indeed seem to be the missing link between the pristine accuracy we saw in old work and what was coming from the hand tools of the day. I had taught myself the method of combining the knifewall with a chisel cut angled low toward and into the knifewall that thus created the slight step-down I needed for saws and chisels to register against. The step meant that the shoulderline could be progressed deeper into the sub fibres of wood being cut.

The knife and square—perfect partners!

 

I wanted something that would replace the term knife mark because, well, knife mark just did not quite cut it. It was teaching that changed my consideration of how we approached the creation of good joinery by hand. Such was the reality that many things ordinary to me needed a boost to a new level. The commonplace things craftsmen often took or take for granted, like ‘knife mark’, needed a reality check. Was ‘knife mark’ right or did it need a brand new word? It did!.

The knifewall is finally given a rightful name after centuries of use.

Mark just did not cut it in the way I needed it to. Mark meant more to mar rather than slice-cut crossgrain to the long axis of the grain of the wood. Something had to redefine what was taking place because the shoulderline markings we did in school with a pointed piece of steel or a dull or dulled blade seemed far from being an apt tool for accurate levels of workmanship, not at all what a craftsman needed. I could never mar the wood with a broadish bruising stabbed at a position. What we needed was a definitive cut line parting off a pristine wall and then too something that definitively said exactly what it was—knifewall!

The shoulderline becomes the step down to accept chisel and saw cuts alike.

Crispness is critical to shoulderlines, so to develop that level of crispness meant developing an attitude towards sharpness and sharpening. The term has become more commonly used for defining the work itself.

The chisel removes the fuzziness and the shoulder meets the stile perfectly. You can see the knifewall at the shoulder’s edge as crisp as can be. Laying the chisel on the knifewall gives the perfect registration that guarantees accuracy.

Whether it will ever make the Oxford or the Merriam Webster dictionary requirements remains to be seen and is perhaps doubtful, but woodworkers around the world use knifewall in their work today even if they only need to say it in their heads as they work!

28 comments on “What’s ‘Knifewall’?

  1. It’s brilliant in its simplicity, Paul…absolutely brilliant. The name conjures an image just as was photographed above. As you have taught many of us, the craft is distilled down to the basics. All else grows from those basic tools, basic techniques, and basic nomenclature. Once a person has command of the basics, then he/she is only limited by their artistic imagination.

    Thank you for everything!
    Chris

  2. Great illustration in the last image to demonstrate the knifewall’s reference for the chisel to clean up the fuzzy bits from the saw. The team’s visual production techniques have become absolutely first rate.

  3. Paul Sellers and knifewall are almost synonymous. Although this technique may have been around before Paul, but it is he who popularized the precision technique to tens of thousands of hand tool woodworkers.

  4. Thanks Paul. Those two photos (with and without the square) really illustrate the waste side brusing that you talked about in the article and in your videos. I have always believed you on this. Seeing the photo of it was very nice.

    Completely unrelated to this. If James Harriott cane write several books (and have a tv show) about his life and times as a vet in the UK, I think you could write a very enjoyable book as well. Much of your posts contain details. For Christmas I received Nancy Hiller’s book Making things work. It is an enjoyable read. Made me think of you.

  5. Question:
    In making a shoulderline, let’s say the chisel goes just below the bottom of the knifewall depth. That means the wedge of waste the chisel creates on the waste side is still attached by uncut fibers to the wanted side. Does that call for 1) another pass with the knife to cut those fibers, or 2) flicking the chisel up to break those fibers? Thanks.

    • Use your thumb to flick them up and out of the way as we see in Paul’s videos.

      If you use the chisel you risk marring the shoulder line.

      In reality some fibres do remain but the step-down is well enough established for setting a saw into, and if using a chisel to create a housing-dado, for instance, then subsequent chisel strikes will remove the stray fibres as the chisel goes deeper into the cut.

      If you wanted a clean step-down you could indeed use the knife again to remove those pieces remaining after the essential thumb flick, and I often do as it deepens the knife wall further which can help with chisel registration when cleaning up the fuzzy bits after sawing.

    • The idea of the chiselling is to use the bevel part of the chisel more as a ‘splitter‘ so there is no need to aim for meeting the bottom of the knifewall but more to aim below it. You will feel it part and then just flick out the material with your fingertips and thumb. This then reveals the setdown you need to rest the saw in or place the chisel against the new knifewall. Dead simple! Of course you can make a deeper knife cut if you want to.

  6. Paul, when I took your classes back in Texas many years back, I didn’t realize that knifewall was a relatively recent term – at the time. I just gratefully adopted it, along with the concept, and continue to use it to this day. The knifewall and the many other concepts that you shared have improved my woodworking and greatly enriched the hobby for me. It’s nice to hear about its origin. Thank you.

  7. Just to add an observation on the technique.

    I learned quickly that if you don’t hold the knife side that is against the square or rule blade at an accurate 90°, you cut a “V” and knife will act like a wedge and push the square or rule off the intended line.

    You must keep the side of the blade at a 90° angle to the wood surface or you won’t get a true straight line. I catch myself letting mind wander when I should be concentrating on keeping that side of the knife blade at true verticle.

    Many thanks Paul for your continuing to educate woodworkers and keeping the tradtions and skills alive.

    • After reading Paul’s post yesterday, I decided to do an examination of my technique. I made three knifewalls across a piece of poplar using the American version of Paul’s Stanley knife. They really looked good. Crisp, and straight.

      Then I got out my jewelers loupe and took a look at them. While they looked fine to the naked eye, the loupe easily showed they made a perfect “V.”

      It took about five minutes to adjust my technique with knife and square to get the same kind of cuts Paul shows here. Paul’s pics provided the standard, the loupe provided the feedback, and from that point it was easy.

    • The other tip is that the first cut really does need to be light, again to prevent the blade pushing the rule off-line.

  8. I know I had never heard the term until I ran across one of your videos several years ago now. I had used only pencils until then for wood and a scratch for metal. I never liked the scratch for wood so never used it there. The few striking knifes I used done no better than the scratch so it was pencils for me. That is until the knifewall was discovered by be through your videos and explained by you.

  9. Paul,
    Great article. it completely re-enforces the process you use in all of your videos. Thanks for breaking out the “crayons and construction paper” to simplify it further.
    I have a question concerning your knife.
    Is the blade flat on one side and bevelled on the other so it references against your square, or is it bevelled on both sides and you angle the blade to achieve the shoulder of the knifewall?

    Thanks for ALL you do for us!!

    • It is beveled equally but in my view one can just continue sharpening one side only so that you have a single sided bevel. I prefer not to because I use the knife other ways too and sometimes left handed.

      • Thank you Paul!!

        I see the idea for both ways. Double bevel equals multi tasking. I think I can follow your examples and use the double bevel to my advantage(s).

  10. The knifewall as others have stated is a revelation. I could never get the precision needed in wood working until I discovered Paul’s technique. I dare anyone to try and get the perfection the knifewall gives using a machine, be it a saw or router. Thanks Paul

    • Have to agree with this – the knifewall gives me a precision I didn’t think I’d ever to achieve without a lifetime’s practice.

  11. Thank you. Now I think I get it! |And am wary of the marking/striking knife I inherited from an old friend of my mothers.

    One question however I don’t get (please forgive me if you covered it and I read too fast): Why not use a knife with a bevel only on the waste side so it runs flat and verticle against the square?

    In my youth I went to bookbinding classes with a craftsman who had done a seven year apprenticeship and boasted he could slit the thickness of a piece of paper. He showed us how to make knives by grinding down broken mechanical hacksaw blades. We used this for paring leather on a flat stone, aiming to get to tissue paper thickness. This grinding resulted in a flat side on what would be the underside of the knife when used horizontally.

    Likewise my old dissecting kit cut-throat razor was flat on one side so one didn’t crush specimens when cutting a section for the microscope with the leaf or whatever embedded in wax.

    Wouldn’t this work and perhaps enable a more reliable vertical cut? I don’t trust myself not to wobble at an angle!

  12. Paul- It’s easy enough to run a knifewall all the way around a piece when cutting square. Strange as it may sound, I still find it confusing when I need to carry a knifewall around a corner when layingout a 45-degree miter or some other non-90 angle. It’s not so clear where to register the knife anymore or how to lean it because of the angle. If you knife in the 45 miter first and then try to go square across the adjacent edge, your knife will cut into the non-waste material on the other face at the corner (on one of the corners, at least).

    May I request a short technique video in which you show how you maintain high accuracy when knifing mitered cuts? This sounds trivial, but I think if you pay attention the next time you knife a miter, you’ll find you are doing a number of subtle things unconsciously that would benefit us if pointed out in detail. I guess this is an issue for both miters and bevels. Maybe mitres as well as miters, too.

  13. the second advantage of the knifewall is the dead on accuracy of layouts. I saw your mortise and tenon joint video on youtube and thought it would take a lifetime to layout like that. My first project was a small trestle table raised cat bed that I built with my middle schooler son. All my mortise and tenon layouts would meet the starting knifewall after going around! and all my joints came out plumb and square. Never had such accuracy with my pencil or scratch awls.
    Thanks for this advance in woodworking.

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