What CELERY Can Teach You About WOODSep 23, 2023
What if I told you that WOOD…is actually an awful lot like CELERY . And that if you’re new to carpentry and woodworking, I think the fastest way to understand the quirks of wood, is to simply observe the nature of celery.
I’ve talked about this before in my rip vs. crosscut video. But that one didn’t get a ton of views, and I thought I should really revisit the subject. This article and video from The Honest Carpenter will reveal the hidden similarities between celery and wood.
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When I see newcomers struggling with concepts in carpentry and woodworking, I often realize that, underneath it all, what they’re actually struggling with is the nature of wood itself.
When their cuts go bad, when their projects break or become unstable, in many cases they’ve simply failed to understand the material they’re working with They overestimate its strength, they ignore its flaws, and they ask it to do things it doesn’t want to do.
When cuts go bad, when projects break or become unstable, in many cases it's simply failing to understand the material being used.
I'll admit, it takes a while to get that ingrained sense of how wood will behave in a project. You can spend a lifetime studying it. But I seriously think one of the most helpful ways to understand the rudiments of working with wood, is to simply compare it to celery.
Celery is not intimidating. Most people are more familiar with cutting and handling it, which is what makes it such an easy entry point for understanding wood.
So, what do these two seemingly unrelated plants have in common? The biggest thing, really, is CELLULAR STRUCTURE.
As I said in the Rip Vs. Crosscut video, wood has a longitudinal grain—you can see this on the face of a milled board. Grain patterns display as long lines extending from one end of the board to the other.
Wood has longitudinal grain, which exists for transporting water and nutrients, and drastically affects how both materials respond to stress (cutting or breaking). Celery is much the same!
This is because trees grow in this linear fashion, projecting upwards from the ground. And unlike the clumpy shape of human cells, tree cells are actually shaped more like long bundles of tubes or straws. These tubular cell groups, known as xylem, transport water and nutrients from the roots, up through the trunk, and into the leaves.
Xylem, tubular tree cells, transport nutrients from the roots to the limbs and leaves.
Celery is much the same. It contains way more water overall. But it too has long, tube-like cells—a xylem and phloem—that also give it an appearance of linear grain.
If you zoom out, the two plants even look alike from a distance. They both contain a root ball with spreading tap roots, a trunk or stalk, and leaves. So, a celery is just a little tree.
Celery have tube-like cells—a xylem and phloem—that also give it an appearance of linear grain.
And that’s all really cool. But, why is this significant?
It’s because that longitudinal grain, which exists for transporting water and nutrients, also drastically affects how both materials respond to stress—especially the stress of cutting or breaking.
The easiest way to cut both wood and celery is WITH THE GRAIN. In other words, passing a saw or blade through it, parallel to the grain structure. In carpentry, we call this type of cut a RIP.
The easiest way to cut wood is WITH THE GRAIN. In carpentry, we call this a RIP cut.
Any new carpenter or woodworker can tell you that rip cuts just feel easier. You feel less resistance on the saw blade when you rip. The cuts naturally come out cleaner, and they don’t present quite as much tear-out, or shredded fiber on the face.
But if you want to see WHY this occurs close up, just try breaking a piece of celery lengthwise. Get a long section with square ends, pinch the two lobes, and spread them away from each other.
It's easier to split celery and wood with the grain, because you're only having to break one line of grain. The stalk will split without a lot of effort. Sometimes you can just snap it straight up the middle. And you can do this even more cleanly by scoring a line down the center first.
This is because we’re just splitting the bundled tubes apart. You’re exploiting natural divisions in the material.
And ripping wood is much the same—the linear grain produces far less resistance to the blade passing through, because you’re only having to break up one line of grain—or one localized bunch of cells.
Splitting wood with the grain works to our advantage.
This is also why it’s super easy to split logs from the top. With a sharp axe, nearly anyone can get the hang of busting up logs. You’re just using force and a sharp edge to part the linear fibers. And this all works to our advantage as woodworkers.
But, the weakness in this dimension also creates problems when you build things out of wood. And this is where I tend to see new DIYers getting things wrong, because they may not acknowledge, or perhaps even be aware of this weakness.
For instance, new DIYers may create structures with really big overhangs along the grain—like this:
BAD IDEA! Hanging longitudinal grain is prone to fracturing because all the extended weight is only relying on a couple grain lines for support.
That’s a big cantilever, and cantilevers need to be really strong to maintain support.
But, hanging longitudinal grain out like this is a bad idea, because...it’s very prone to fracturing. All of that extended weight is relying on a couple grain lines for support. But those linear fibers will separate under nominal weight or force, usually right near the supplied fulcrum.
Deck stairs unsupported along the linear grain are prone to break off.
This is why the front edge of deck stairs are so prone to breaking off. I replaced numerous deck treads over the years because the treads are often extended too far over the riser below. They’re unsupported along the linear grain at the edge.
Split the wood for faster removal.
And that’s why I also showed in my deck stair repair video that I often won’t even unscrew treads to remove them—I’ll just split the wood at the fastener, because it comes apart so easily this way, and you can remove it in sections.
Short pieces are even worse about this. Often a single nail in them can cause them to split, especially if it’s treated lumber that has dried out quickly.
Often a single nail can cause pieces to split.
And, thin cross-sections are REALLY prone to snapping. They’re so brittle you can often break them with your fingers—just like you could with a wedge of celery. Cut a little sliver, and you can break it with the gentlest force.
So, that’s where both wood and celery are weaker—with the grain. But if you want to see where they’re both extremely strong, just turn them 90 degrees and apply force.
By presenting stress ACROSS the grain, you reveal the hidden strength of the cellular structure.
By presenting stress across the grain, or perpendicular to it, you reveal the hidden strength of this cellular structure. Because that point force is no longer acting on one linear bundle of cells—instead, it’s acting on all the cells across the width of the piece.
The point of force is acting on all the cells across the width of the piece.
Celery will bend when force is applied this way. It won’t break easily like before—because it actually has a lot of elasticity and toughness.
Bending celery across the grain makes it much more difficult to snap.
And even when it does finally break, it won’t do so cleanly. It actually tends to shred. Because some individual fiber groups break, but others hold strong. You have to apply a lot of force to finally tear it, and you wind up with a mess. Even cutting it across the grain requires a sharper blade, and careful attention to make sure very fiber is parted, because the celery puts up a fight.
Wood is exactly the same.
Severing wood across the grain is known as crosscutting, and it’s more difficult overall. Saws struggle more to make the cut. Motors face more resistance, because they’re now having to sever every single little connection in the wood, from one side to the other.
Crosscutting requires extremely sharp blades, cutting very slowly, saws struggle more, and motors face more resistance.
And you have to use very sharp blades to make crosscuts, and make the cut very slowly. Because if you use a dull blade, or make the cut too fast, the teeth of the blade will shred through the wood, and get lots of tear-out.
Crosscutting too fast can rip the fibers.
Again, each individual saw tooth is responsible for tackling a new layer of cell fibers. And if you go too fast, you won’t actually cut those fibers—you’ll just rip them apart. Your cut will look extremely ragged, like a stalk of celery you broke in half.
If you cut across the grain too fast or with a dull blade, your cut will look extremely ragged - like snapping celery.
So, crosscutting and shaping wood across the grain is harder. You need to go much more slowly, and use very sharp tools. But, as I said, this resistance to separating across the grain also means that wood is much stronger in this dimension.
Maximizing strength! Turn any board off its flat dimension, up onto its wider edge, stacking layers of cross-grain.
Wood extended perpendicular to an edge will present a much stronger cantilever over time. And, if you REALLY want to get the maximum strength this way, you can turn any board off its flat dimension, up onto its wider edge.
Now you can produce real, structural cantilevers. Because you’re stacking up layers of cross-grain, all bonded together. Each one supported by and supporting, the one below it. This is how whole structures are built, and I’ll talk about it more in the future.
But, that’s the power of this linear cell structure, and it’s all pretty well illustrated by our pal celery, the little tree you can eat.
Now, eventually the celery metaphor breaks down. For instance, wood warps under certain conditions...I actually did a whole video on why and how it warps, so check that one out, because it’s actually an interesting topic.
Warped wood changes things.
But, I’m not sure if celery warps because I never keep it around long enough to find out.
Also, in the U.S. we build lots of structures using narrow wood pieces—studs—as vertical supports, because it has great rigidity in this dimension. But celery, I’m afraid, is probably a little too flimsy for use in building elevated structures.
Celery does, however, go great with peanut butter. Whereas wood requires LOTS of peanut butter to become even slightly palatable.
But, that’s my food/carpentry lesson for the week. I hope it was helpful. Let me know what you thought of it down in the comments
The power of this linear cell structure!
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