Hirota’s Fuigo

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Interested in making a fuigo (Japanese box bellows) for your forge? Mark Grable has an old fuigo from a saw smith friend of Yataiki, Hirota. This is the fuigo that John Burt used to build a copy for Yataiki in Iowa, and its worth studying if you want to build your own because there are many technical refinements in shape and joinery that are very important to how the bellows is used, especially when it comes to pumping the bellows with your foot during yaki-ire.

I’ve made a fuigo myself, which you can find by searching the fuigo category on the left of the page. If you’re not too familiar with their construction your understanding of the following details will benefit greatly by reviewing and watching the John Burt video.

I’ve seen a lot of modern fuigo at this point, that while quite useful and functional, fail to meet the potential of what this tool is capable of as part of the total context of how a Japanese smith would work at the forge. The most common thing I see lacking is size, this fuigo measures nearly four feet long, with a total length of 116cm, and an internal displacement cross section of 25cm wide by 56 cm high.  Its made from top quality vertical grain Japanese cypress. The top and bottom are each a single board, and the long sides are made from two boards joined together.

Understand, fuigo are made in many different sizes, all the way from the monster bellows used in tatara production of tamahagane to the tinsmith’s tiny backpack bellows, but its worthy to note that Yataiki asked Burt to make a fuigo three inches wider than this one. By comparison, the fuigo that I made for my forge is about three quarter scale of this one, due primarily to the constraint of needing to store it out of the way on a shelf while not in use.

 

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The handle fits on a tapered round tenon, with the hole drilled in the handle at a slight angle so that it faces the smith more directly. In addition, there is the all important foot board on the piston shaft. This is what the toes of the smith’s foot rest against while pumping the bellows with the left foot, leaving both hands free to manage the coal bed and manipulate tongs.

Notice the groove that’s been worn in the handle by so much use? Respect.

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I originally thought that this board was simply held from slipping up the shaft by the taper of the tenon, but in this case it is evident that a nail was used to back the foot board up.

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Evidently a t-shaped cut nail by the looks of the damage to the bearing board, haha.

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In fact, the whole fuigo is assembled with nails, with some very interesting nails with an extra wide head used on the sides and birdhouse top.

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Another important detail is the curve to the sides. Its easy to say that the fuigo sides are curved both in length and height, but how much?

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Finally I can measure a working fuigo to get my answer, and it surprised me a bit. The long sides have a total deflection at the center of 5mm, and the total deflection of the height along the short sides is 2.5mm. Further more, the long sides taper in along their length 10mm! If the need for the curve to the sides can be ascribed to counterbalancing the internal pressure of the air bowing outward, perhaps the taper is due to the action of the foot pumping the bellows with a limited stroke with the piston rod almost all the way to the back of the fuigo.

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Looking at the bracing on the top I have often wondered why the front is boxed in, still not sure, but I do notice is that the battens are nailed only on the outside edge where the nails will come through outside of the dado’s that house the side panels. On the lower left there’s quite a depression that has been formed, perhaps by many years of a hand resting on the corner?

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Looking at the bottom of the fuigo top we can see the dados. I placed a straight edge against the outside edges and they have a bit of curve to them as well, not as much as the dado’s themselves, but just about what you would expect if you first planed the curve on the outside edges and used them as a reference for marking the grooves with a gauge, and then made the outside edges a bit straighter during finish planing.

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You can still see the saw kerf at the bottom of the groove from the azebiki nokogiri that was used to saw the dado lines. Haha, not too fine of a cut at the bottom, pretty much chiseled out quickly.

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One of the more subtle refinements is that the top edge of the sides as well as the dado’s in the top board that house them are tapered. After all, the top board is secured with only a pressure fit, but still needs to be removable and create a good seal against the internal pressure of the air when pumping the fuigo.

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And of course, the piston board is wrapped with raccoon fur, probably attached with rice glue.

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And the front stop for the piston head is about one third of the way down the fuigo. My guess on why the whole length of the box isn’t used has to do with the length of stroke that the human arm is capable of while seated, as well as the need to keep the piston board from jamming on the push stroke by keeping the bearing points separated by a bit of distance at all times. The piston rod bearing wasn’t a great fit, but that probably had more to due with the wear this fuigo has seen than any design consideration.

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A lot of the chamfers on this fuigo are shallower than 45 degrees. For example, the chamfers around the flapper valves that let the air into the bird house leave 5mm of side thickness untouched, when the total thickness of the long sides is 9mm.

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Although, the front and back flapper valve holes are not chamfered, not sure why. There is however gasket material sewn on to the front and back of the flapper.

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The dado’s on the top aside, the quality of the fits on this fuigo suggest that whoever made it knew what they were doing. Take, for instance, the fit of the bearing block to the curve of the long side, not a right angle. Similarly the edge birdhouse top is beautifully fitted to the curve of the long side panel, not a gap in sight, and consider that the long sides curve both in length and height.

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The joinery that connects the long side by the birdhouse to the short side is the trickiest bit, a half lap with concurring dado’s that slide together. There’s an extension on the long side that is quite weak, and I had one of mine snap off because of the tight fit of my joinery. It was beautiful to me to see that this had been taken into account by the craftsman by shaping the extension so that less wood rubbed against the short side panel (although there was still a crack here, haha).

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The last detail that I’ll discuss today is the air exit that connects to the carved kiri tuyere. Its tapered to fit the conical section of the kiri tuyere adapter, and also angles slightly towards the front of the fuigo. Why the angle? Perhaps it has to do with the length of the fuigo relative to the placement of the fire. The hole is also not centered on the length of the fuigo, lying slightly towards the front.

I hope this information is of use to those making fuigo for their forge. I took a complete set of measurements and drawings in metric which I’d like to draw up into a set of plans. Let me know if you have any questions, I’ll do my best to answer.

Sen and Sen-Dai for Hand Scraping Saws

 

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This is going to be a post with a lot of pictures, hopefully it won’t take forever to load on your web browser. To start, a method for measuring saw plate thickness, basically a red-neck deep throat dial micrometer using a drill press. By setting the zero on the dial to the thinnest parts of this saw I could write the deviation in thousandths directly on the plate, a grid of numbers. Supposedly this kind of saw plate variation of thickness for western panel saws is unusual, but it offers me a good opportunity to discuss the Japanese tools used to hand thickness nokogiri.

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With the grid of the saw mapped I built up a topographical map to better visually represent the variation in thickness. After all, if you’re going to scrape a saw evenly you need to know where to take off metal. This saw already went through quite a bit of hammer straightening, but the problems with the uneven thickness of the plate are making it difficult to get that last 10% of straight. The normal fashion for gauging proper thickness on Japanese saws is to bend the saw and observe the curve, and I can attest that this is, with appropriate experience a la Yataiki, an extrememly accurate way to thickness saws to within a thousandth of an inch, based on some of his saws that I have looked at with the dial micrometer.

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The tools used to scrape the saw plates are sen. You’ll find that these were once very common tools to all of the tool making blacksmith trades, including katana and kanna. Some of the sen pictured here are specialized for saw making, like the one at the very bottom of the frame, but there are others that could be used for hand scraping the ura (hollow) on the backs of Japanese chisels and kanna, or the flute on the sides of a katana.

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This particular set uses laminate construction with Swedish steel.

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And the final stage of scraping involves a lot of work hand burnishing the surface with a lot of pressure and elbow grease.

What kind of Swedish steel I would very much like to know, seeing as saying Swedish steel is about as useful as saying they are made from high carbon steel, there’s a lot of different kinds out there these days.

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Lets start with a frame of reference for what the hell I’m talking about. This is a photo of Yataiki thicknessing a saw at the sen-dai. Beautiful metal shavings, no? The sen-dai comprises both the board the saw is resting on and the staple vise used to hold the saw flat. The large staple goes over the sen board and is mounted into a foundation block of poured concrete in the ground, a large block about two feet wide by four feet long, very stable.

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For holding the saw down flat to be scraped on the sen-dai there are lots of little spring clamps and wedges. These are all used under the staple of the sen dai. The ball bearing is for rolling vigerously in hand to prevent blisters, the loop of steel is a way of binding the handles of a pair of tongs when forging. The little rectangular wedges hold the sen board against the wedge beneath it that gives it the proper downward angle for work.

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For holding the opposite side of the saw nearest where you would be seated are more spring clamps, elegant little pieces of spring steel that slip over the edge of the sen board.

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Saw makers don’t make one saw at a time, its more of a production affair. Here is a good stock of rough forged blanks, ready for rough grinding after the tangs are forge welded on.

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An elegant spring clamp in use.

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And under the staple the various wedges. The spring wedge holding the tang down has a curl at the other end used as a snell, for tapping the wedge loose.

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This is just a mock up of the sen-dai. There is one size of board for larger saws.

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And a smaller, thinner board for dozuki. Both of these are made from Kashi, Japanese white oak, the same wood used in plane dai.

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The staple spring clamp for dozuki have a variation with a little stop cut at the end that the blade butts up against.

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That allows for working right up to the end of the saw plate.

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In the past all of the thicknessing would have been done by hand. More modern methods involve a rough surface grinding to remove most of the excess material. Here is a ryoba saw, rough ground and tempered. Beautiful colour.

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Apparently dozuki are differentially tempered, softer along the tooth edge.

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What you’re seeing here is a dozuki blade that’s been hammer straightened after tempering with two different kinds of hammers. Fascinating surface!

 

Note: This post has been edited to correct an earlier mistake, referring to Japanese Oak as Keyaki (a type of Japanese Elm) instead of Kashi.

Splay Leg Stool Assembly

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The last thing I’ve left to explain in the construction of a splay leg stool is finding the length of the rails which connect the legs on all four sides.

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There’s nothing like the moment of assembly to find out if all the careful calculation and drawing work was correct. These splay leg assemblies come together all at once, with all the joints tightening progressively.

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Everything looked like it was going so well, and then the legs bottomed out in the joints and there was still about an 1/8″ of travel left in the rail tenons for the joints to come together. Like I said, moment of truth. The problem then came down to finding out where I had made the error.

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At first I was dumb, and didn’t think about the relationship between the leg length and rails. For every inch that the rail tenons come together the leg tenons have to move into the mortises about two inches…

But like I said, dumb, right? Out came my little saw with no set to try kerfing the joints on the legs to get a bit more travel. I wasted about two hours trying to get the rail tenons together, maybe .020 inch at a time.  Kerfing is a great technique for getting nice tight joints, but the shoulders for the leg mortises needed to move back something like a quarter of an inch. where did I go wrong?

Leg Length Drawing

It was in my assumption that the distance of the rails was measured along the centerline of the top and bottom edges, and I had the drawing all along that showed how I was wrong, but didn’t see it. Funny how that happens. Effectively I cut the rails too short between the tenons. Rather than re-cut new rails, it made more sense to make the legs a bit shorter at the tenon shoulders. Thankfully this is a correctible problem, I’ll just end up with a stool that is a tiny bit shorter than I had intended.

The above excerpt from “How to use the Sashigane” Shows another small stool, with the length of the rail transferring directly down from a elevation view to the view of the rail from the top. Notice how the length points are along the edge? Yeah.

Leg Length

In my own drawing I had the correct lengths, but thought that the measurement point once the stool was folded up along the ground axis on one side was now the center line. I failed to reference the corresponding length of the edge on the other half of the rail. If I had, I would have found that the length does not change along the bottom edge of the rail in either side of the view, elevation to fold-up.

Difference in Leg Height

By placing a trace line on the center line and transferring it up to the fold out view I was able to find how much too long my legs were, a whopping .276″.  There was nothing to it now but to disassemble the stool and re-cut the leg tenons.

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But doing that was not simple either. Seeing as all of the joints tighten together as once, you pretty much need to pull all of the joints apart at the same time. The solution? The humble wedge used under the rails, constantly providing pressure to lift the leg assembly from the top as the rails were tapped apart with a hammer.

In a way I’m pleased this happened, because I ended up understanding the drawing relationships better.

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I had already chamfered the edges of the legs, so it made laying out the new cut lines difficult, but not impossible, and this time the stool assembled properly. It could still use some kerfing on the joints to get a perfect seamless fit, but that can wait until the doug fir I made this from will dry out a bit, as I resawed the material from a timber framing beam off-cut that was still green.

I was looking for a challenge in taking on this stool build, and it doesn’t surprise me that I made some mistakes. In any woodworking endeavor that is often the case, and it equally takes skill to figure out how to fix the problem that was unforeseen. Don’t give up when you run into an obstacle like this! Its something we all learn from, and it will not be the last time I learn from my mistakes more so than if everything went perfectly to plan.

Cutting Compound Angle Mortise and Tenons

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Is modern digital technology running rampant in your life? Grab a saw! Join me for a little work and find out if your mind has been colonized by a corporation.

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I finished the stool yesterday, so time to work through the rest of the problems associated with making a splay legged stool. Its a good thing that I’ve waited to post about this until finishing, because I found a few mistakes I made that were very instructive in understanding this project, which I’ll go into more detail with on the final post of this series detailing the final assembly.

The compound angle of the mortises meant that chopping with a chisel would have presented some great difficulties, so I started by drilling the waste with a brad point twist drill. I used the layout lines on the sides and a straight edge placed on the side for visually aligning the drill.

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Just as you would for chopping with a chisel, drill half way through from both sides to reduce the chance of drilling waste outside the cut lines.

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The table mortises were first layed out on the bottom using measurements from the center lines of the board, with the lines transferring up on all four edges with the common 3.5/10 slope to the top. Because the mortises were too far in to sight accurately I used a bevel gauge placed at 45 degrees in plan to gauge the angle for the drill and its alignment. In this case the angle for the drill, because it is at 45 degrees to plan (top view) uses the displacement multiplied by the square root of two, working out to about 4.9/10 for the angle to set the bevel gauge to.  Why the square root of two? I’ll let you figure that one out, its very, very common in dealing with slopes that are a regular 45 degrees in plan.

To pare the surfaces of the mortises in the top I made a guide block for the chisel at the common slope, which applies to both the end grain and side walls of the mortise. One block to pare them all.

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I tried using the extra leg I had cut as a guide block for the mortises on the legs but found it faster to simply sight along the edge of the leg, and used a big timber framing chisel.

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Cutting the tenons was very special for me because it was the first chance that Mark has given me to try some of Yataiki’s saws. I used a 240mm ryoba for all of the cuts. This saw was very good, to put it mildly. My saws are all mushy disposable blade type, so coming from that to a saw like this is a quantum leap, and I joked with Mark whenever he asked how it was going that I had only broken off a couple of teeth. That is a real concern with lending someone a good saw to use, its no small matter, you don’t just hand a saw like this over lightly, and I greatly appreciated the gesture on Marks part to let me use this tool.

The saw was very thin, light, and finely set. Easy to use one handed, and really did all of the work without me pushing it through the cut. For the first time I felt like I was really experiencing new dynamics of the saw in the cut.

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Should you run across a saw with these Markings…

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Treasure it dearly.

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Yataiki gave this saw to Mark when he was teaching in Iowa for making charcoal for the forge and asking doing things like counting the number of teeth on a saw.

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It has some history, as the staining and hammer marks from hizumi will attest.

As an aside, I’ve been meaning to write a post on Marks hizumi hammers, but have been holding off because I don’t want to be too proscriptive about which hammer is the correct one for a particular task. What is important, besides the weight of the hammer matching the thickness of the plate, is the shape of the cross peen edge. And to that end, its easier to describe the correct shape and size of the mark it leaves than the degree of radius on its edges. Measuring the ghosts of the marks on this saw shows a cross peen mark about six millimeters long and one millimeter wide, an ellipse.

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The yoko-biki (cross-cut) are nice and slender little daggers, really well proportioned.

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The tate-biki are likewise pleasing to the eye.

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My normal method of ripping tenon cheeks is with the piece of wood held vertical in a bench vise, but I found the teeth of this saw too sharp and aggressive to handle the angle of cutting uphill to the grain. The alternative is cutting downhill with the piece held horizontally. The saw horse I’m working on is a bit low for this task but It worked nicely, with the advantage of being able to freely orient to the best light from the south facing windows.

Getting the chance to use this saw was a real eye opener for me. I knew my disposable blade saws weren’t that great, but the positive difference is almost unquantifiable, and I find myself hoping to buy, perhaps not a totally handmade professional grade saw, but something with decent steel that I won’t feel too bad about sharpening on my own. The world needs more saws like this!

Splay Leg Layout

Splay stool elevation and leg foldout

Today we take a closer look at laying out the mortises in the legs of the splay leg stool. Remember that previously from drawing the side elevation the view has been folded up along the ground axis to represent the faces of the leg as truly flat to the 2D plane of the drawing, and then unwrapped so that all of the faces of the leg can be shown at once.

Starting with the basic slope of the stool at 3.5/10 I was able to determine chu-ko slope from dividing the basic unit triangle, forming the slope that the foldout is drawn at, 3.304/10. This is the angle that the bottom of the legs are cut at, as well as the angle that the mortise travels through the leg.

There are no right angles here, even the top and bottom of the mortises have a slight angle, sho-chu-ko, but well see to that in a bit.

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With a non base 10 unit system of measure converting from decimals of and inch to fractions is made much simpler by dialing in the measure on my dial calipers and seeing where it hits on the scale of the sashigane. One of these days I’ll switch to shaku  and metric, but until then I continue with this madness.

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In practice the angle for the bottom cut of the leg looks like this on the sashigane, with one arm holding 3.304 and the other the base unit of ten.

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You need to mark this same angle a whole bunch of times so it pays to fix a bevel gauge to the same angle. I like this stainless Shinwa sliding bevel!

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And to help fix it in the mind you can compare directly to the drawing. Or if the drawing is closer to scale you could take the angle directly from the drawing.

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I took a moment to examine the relationship of the faces of the leg to their orientation, and found that you have to cut two sets of legs. The ones that diagonally oppose each other are the same, all of the angles are opposite for the other pair.

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I never truly understood the elegance of center line layout until starting on this saw horse. Edge rule is fine for orthogonal work (at right angles), but when there’s compound angles your measurements need to be referenced to the center line. For instance, because both the face and edge cuts of the rails are miters the lengths you pull from the drawing are along the center line, not the edge. Suddenly the beauty of this system becomes very clear.

For the placement of the mortises I measured along the center line as well, with some of the measurements easier to transfer directly from my dial caliper.

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With one leg marked I used the edge of my wooden straight edge as a story stick, transferring all of the marks to the stick so that I didn’t have to spend time making all of the measurements again and again. In Japanese this is known as an ‘idiot’ stick. Call me an accurate idiot then…

Sho-chu-ko

For the angle of the top mortise the smallest division of the unit triangle is used, sho-chu-ko. This is the tiny little line on the bottom right of the triangle, forming a new slope of .361/10, or an angle of 2.067 degrees. This one I didn’t lay out directly with the sashigane because the actual angle needed is ninety degrees to the edge of the leg plus or minus sho-chu-ko.

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Functionally its two degrees, so I used a protractor and set another  bevel gauge to the resulting line.

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The width of the mortise is measured along the sho-chu-ko line, not perpendicular to the edge of the leg. That little detail held me up for quite a while, and I had to go back and fix my drawing so that the mortises did not interfere.

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Compound angle joinery is improved with a little beer.

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A two legs from any side of the saw horse are mirror opposites. I’m showing you the nice looking layout, not the ones with lines scribbled out everywhere…

Next is the layout on the rails and top, and then finally I can start drilling the mortises and cutting tenons! I hope this inspires someone else to take on the challenge of figuring this out.