The Mini Sawyer

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A friend showed up today and dropped off a chunk of birds eye maple that had split on him when he felled the tree. I’m not sure what happened to the rest of the tree, boy would I like to know! In any case I found myself in possession of a small piece of wood, and for sure it would make some fine bowls turned on the lathe, but I don’t have access to a lathe at the moment. Being highly figured wood, and a small piece at that, I figured the best use would be to saw into thin boards, either for veneer on drawer fronts or small presentation boxes. With birds eye grain the best figure is gained from flat sawing, not quarter sawing, which also happened to work out to give me the widest pieces.

The problem is, how does one saw an oddly shaped piece of wood like this without a large bench vise as I am accustomed to? I started by planing down the outside face until I had established a flat land worth converting into the first board.

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A bit of the figure shows in the bark, as well as being quite obvious in the freshly planed surface, quite beautiful!

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With one flat face I knew I could use a marking gauge to mark for the cut, but my end wheel gauge doesn’t have a large enough fence to register against, especially when the surface to be marked is sloping heavily away. Luckily the wooden straight edge I made a couple of days ago was at hand, and already had a hole big enough to pass the bar of the gauge through, now the first board could be marked.

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I’ve thought of using a technique analogous to this for marking highly irregular logs, akin to the sled that an Alaskan chainsaw mill uses for aligning the first slab cut.

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After marking with the wheel gauge I darkened the line in with a soft pencil.

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And clamped the chunk of wood to the closest near vertical thing at hand, a ladder to the loft above. You have to move the clamps around a bit as you cut, and keep the kerf open where its clamped with some wedges, but it obviates the need for a large bench clamp. The same function would be served quite nicely by a 4×4 timber, and it could even be made free standing in the shop if you were to add some cross pieces at the bottom for feet.

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The figure became more pronounced as I sawed through.

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I titled this post “The Mini Sawyer” because this is basically the miniature version of what I go through sawing a proper sized log, same orientation, same dynamics of the saw at various angles to the grain. The crossing grain of the birds eye was quite noticeable when sawing, a bit like small pin knots but softer.

For those unfamiliar, the saw that I’m using is a home made Japanese style rip saw, re-purposed from an old western panel saw. The steel is nothing special, but I’ve done a lot of sawing with it at this point, and it does a good job because the blade is flat and I sharpen it frequently. If you’re into Japanese saws you may have run across mention of saws that hold their edge for forty hours, almost mythical stuff, I had to sharpen for every board I cut, sometimes it went dull a couple inches before the cut finished. You know its time to sharpen when the middle of the tooth line is dull and you start snagging on the outside teeth because of the increased pressure of using a slightly dull saw.

I started having problems with cupping in the cut and became increasingly frustrated until I noticed that I had sharpened most of the set out of the teeth, hadn’t been keeping track of that even though you’d think I know what I’m doing by now. Carrying enough set in the saw is seriously important for wide rip cuts in green wood, which as you can see from the photo above tends to cup when flat sawn, especially if the outside surface has had some time to dry and introduce some stresses in the wood. Sawing like this is fundamentally quite different from how a joinery saw is tuned for minimal set. Even the most skillful hand sawyer wouldn’t be able to track a straight line ripping boards in green wood if the saw was under set. How much set is enough? That depends, but generally its towards the maximum that the saw can handle for the thickness of the plate, I tend to run this saw at about 2/3 of maximum set because I also use this saw for seasoned lumber. Don’t feel bad about the wider kerf, its peanuts compared to the extra wood you’d have to plane off if the plate gets pushed around as the wood warps in the cut.

I stickered the boards as I cut them to keep the drying even, and stacked a couple of really heavy slabs on the hole affair to keep things flat as they dry. My stickers aren’t even in the photo below, they should be directly over each other or you could end up introducing warps into the slabs as they dry.

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No band saw involved, no great fuss, just time, effort, and paying attention to the saw. Its your best teacher.

Those Legs Ain’t Square

Splay Legged Stool

Starting now on a new build thread, a Japanese splay leg stool. Why a stool you ask? A splay leg saw horse is in the series of exam challenges for a Japanese carpenter after a ‘hopper’, introducing the fundamental concepts of working with compound angles that are necessary for the complexity of understanding and laying out hip roof framing. I merely chose to make a stool as opposed to a saw horse because horses are best made in sets of two, and a stool takes far less lumber. Plus, I’ve felt the need for a short stool to sit upon while sawing lumber (oddly enough two identical stools would be better for this task as well, but one suffices).

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I’ve cut a roof in the past where I ran into some of these compound angles and used several modern western books to understand the layout, which has gotten me by just fine. But the Japanese methods for some reason just make more sense. And I want to cut timber frames inspired by Japanese structural joinery.

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To avoid some awkward geometry where the rails meet the legs the footprint of the legs are made square to plan (the view seen from above). As a consequence of the leg being splayed, tilted at an angle in two axis, is that the cross section of the leg becomes diamond shaped.

So, how does one figure out the right shape to make the leg? Lets pull back a minute for a bit more introduction to rise/run and the hopper shape.

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Here from the Japanese text “How to use the Sashigane” is a picture of two different hoppers, a mitered hopper and a butt edged hopper. The geometry of this form applies to a splay leg stool as well, which you might come to see as a hopper turned upside down.

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On the left page is the introduction to slope expressed as rise/run, just as you might use in describing a roof in the west as 6/12, or 12/12. For a base unit run of 12 the roof rises, or displace, a given amount, and the pitch of the roof that keeps the rain off your head is defined. In the rest of the world run is defined with a base unit of 10. So in the case of the hopper in the photo above for a base unit of 10 it has a displacement of 3, or a 3/10 slope seen in elevation (side view).

Given that basic relationship a triangle is formed, with the two right angle sides defining the hypotenuse (seen on the right page above). In the Japanese system each of the sides of this triangle is given a name, ko , ko , and gen 玄.

By further dividing the unit triangle the slope angles for compound miter cuts can be found. The first division, cho-gen, is made by drawing a line perpendicular to the hypotenuse (gen) which intersects with the right angle corner of the rise/run. In the text above they help you out by assigning cho-gen a square shape. Knowing this length allows you to form a new triangle that gives the face cut angle on a hopper, or the angle that a rail meets a leg for the stool that I’m making.

By using the base unit of 10 on one arm of the framing square and the cho-gen length on the other, a new triangle is formed and you descend down the rabbit hole of ki-ku-jutsu! Fun times! The sashigane is your calculator, no math required. Similarly the edge miter angle for a hopper (or the edge miter of a rail meeting a leg) is found in the same unit triangle with the division of the hypotenuse by the cho-gen line.

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Want to know more about this without searching for obscure Japanese carpentry texts? Chris Hall has published a great series of texts here. I’ve only bought the second one, and its helped me tremendously. Help a brother carpenter out and send him some love (and by love I mean money).

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This page shows one good method (far from the only way) to find the correct shape for the leg of my stool. What they’ve done is folded the sides of the leg out like opening a cardboard box and layed it flat to represent it accurately in two dimensional form.

Using the width of the leg along the ground a square box is drawn. Next a line is drawn diagonally that represents the outside arris (corner) to the inside arris. By taking the width of the leg perpendicular to its length with a compass and swinging it down to where it intersects the diagonal the first of the corners can be defined. See? This shit all boils down to basic geometric concepts and you should be able to fill in the rest of the leg cross section from there. The photo above also shows the method for laying out the rail mortises so that they do not interfere, as well as an interesting way to find the angle of the top and bottom edges of the mortise (sho-chu-ko, a further division of the unit triangle).

But how does one draw the foldout view of the leg at the right angle in the first place? It is in fact not the same as a simple elevation view, remember that in elevation the leg is leaning away from you, so the true lengths of the joinery along the leg cannot be taken directly.

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Here is the elevation view, and they’ve done something really cool. Can you tell? They’ve folded the whole drawing on one side up along the ground axis so that the leg face is represented truly flat/vertical! If you were sitting on the ground in front of the stool its like leaning the whole stool towards you. In elevation view the leg is defined by the common slope (3.5/10). By projecting a vertical line along the slope of the leg a point is chosen along the slope and swung with a compass up to meet the vertical line. Because any given point remains consistent along the vertical axis you can now draw the face of the leg so that measurements along its length are accurate.

Notice that the leg is now at a new slope. If you were to take your sashigane and measure this new slope, what would you find? Its our old friend Chu-ko slope! Okay, too much exclamation, but this unit triangle shit is pretty cool. This is the same slope used to draw the foldout view of the leg. There’s more important detail to the above drawing, but I’ll save that for when I get to the rail tenons.

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Back in the real world I became a little suspicious of the accuracy of the straight edge on my sashigane, must have dropped it again…So I made a simple wooden straight edge long enough to draw the center lines on my stool legs, about 24″ of vertical grain doug-fir, the same lumber I resawed for the stool.

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The two halves are cut from one piece, book matched, and match drilled for dowels that are glued in one half. The dowel is a good tight fit and allows the edges to be planed together.

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By planing them when they’re together any deviation from straight is doubled when viewed with their edges together. Its a simple technique and beautifully accurate. Its accuracy that you can really trust because you always have a reference edge to check it against, no wondering how straight it is, check that shit and be sure. The side with the glued dowels is the reference, in practice only the other half is used to check flat and draw straight lines.

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I used the same method I explained above to find the cross-section directly on the end grain of the leg, and inked a line on the faces to show how much material to remove. In order to know how close to meeting the other edge I was while planing I used a pencil to darken the wood. When the pencil graphite is gone you’ve planed out to the corner.

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Five legs (one spare for when I fuck up), ready for layout, a post for tomorrow. If you think this was complicated enough prepare to join me further down the rabbit hole.

X Marks the Spot

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For the past day or two I took on the challenge of drafting a carpentry drawing exercise of Bruno Sutter’s, a compagnon, detailed by Chris Hall on his blog thecarpentryway.BlogSpot.com, in a series titles X Marks the Spot.

Its basically one of those great blog series of Hall’s that seem irreducibly complex even after reading through several times, but there had to be a reason for him to present the material. As it turns out, its not terrible compared to a Mazerolle sawhorse, and teaches many important descriptive geometry concepts for a relative neophyte such as myself.

Its not worthwhile to rehash the how-to of this endeavor, Hall does a very thorough job himself. What I do want to get across is the importance of actually doing the drawing work if you want to understand how this works. I’ve made inroads with using Google Sketchup for drafting, as well as by hand, and have things I like about both.

  1. Sketchup is free, fast, and accurate (with the exception of certain functions regarding curves and circles), but doesn’t work without a computer.
  2. Hand drafting was the only option until a generation ago, and our carpentry forbearers managed much masterful work. That said, its easy to accumulate small errors in accuracy even working full scale, such as when projecting a line long distance from the edge of a footprint. While you can draft with not much more than paper, pencil, straightedge, and compass, you’ll definitely find it more manageable with stuff like a T-square, parallel rule, drafting triangles, protractor, scale ruler, and a range of hardness in pencils or line weight of pen.

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For this exercise I decided to work it out on paper, best to be familiar with both ways of working, you never know when the zombie apocalypse will take out computer functions…

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My drawing, mostly completed. Notice how hard it is to see? That’s because I’m using a very hard sharp pencil for accuracy, with the paper taped down nice and flat to the edges of the drafting board.

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The basic sequence of the drawing consists of starting with a plan view of the two crossing sticks, using the cross section to find the footprint via folding down the elevation view, and then finding where the planes of each of the faces on one stick intersect the other. By unwrapping the stick like a cardboard box layed flat the lines of intersection can be transferred, and each of the faces shown as if you were looking at them directly.IMAG2226

The drawing is to scale for the size of the pieces I wanted to use, one inch square in cross section and a little over a foot long. The advantage of drawing to scale is that the pieces can be place on the drawing and marked directly. Pretty neat, no?

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The last step of actually figuring out what bit of wood to remove presented the greatest difficulty. Hall says that you basically have to ‘intuit’ from the planes of intersection what represents the actual cut lines. My spatial skills are not quite there yet, so I made the miter cuts at the end of the sticks and held them close together in their correct orientations until I could see where one piece fit through the other and shade in between the lines.

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On the unflolded view of the drawing the planes of each of the faces of the opposing piece are marked in blue and red, with the resulting space that needs to be cut out shaded in green. Not exactly jumping out to you that these are the cut line for one square piece of wood fitting through another, but that’s what happens with stuff at slope and differing angles to plan.

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Cutout was a petite masterclass in cutting angles. I basically cut all the lines I could with a ryoba saw, and then went in with a fret saw for the bottom line that can’t be reached with a normal saw. Paring a bit with a chisel and voila! Not a piston fit, but at least it shows that I understood the drawing exercise. I had to draw this whole thing twice because I noticed my first drawing wasn’t accurate enough, lines that should have been parallel were not, and the cuts would have been all fucked up as a result.

If I wanted to do really accurate work? Computer drafting is the answer.

Splay Legged Stool

Like, say, a splay legged stool? Yup! I figured out the kinks on this one too, but it deserves much discussion of its own, so I’ll save it for next time.