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!

8 thoughts on “Cutting Compound Angle Mortise and Tenons”

  1. Thanks for the great pics of the Yataiki saw, a delicate beauty for sure (you lucky bastard)!

    There are many saws on yahoo auctions that bear the distinctive washed out Miyano inscription on the face side of the saw. I have wondered if that characteristic is an idiosyncrasy of that particular school of saw making, related to the process. I assume that it is a direct function of the thinness of the plate, as stamping after the grinding/sen stage would distort the blade too much. On my thinner saws, even the delicate chisel cut inscriptions cause deformation that shows through the opposite side.

    Your pic of the back face is what distinguishes it as a Yataiki saw I think, and highlights the masterful scarf joint as well. There’s one now on yahoo that could be yours for an opening bid of ¥50,000 (or BIN@ ¥70,000….only $641 USD haha ). Cheap for his stuff, maybe because of some question of authenticity. A great tool.

    Really nice work that you are doing. Thank you for sharing it.

  2. I approximated it to 5/10, the same slope that the roof has.

    The saw has been sharpened by Mark I guess? I love the way the set hammer marks appear there.

    Definitely don’t have a saw with those marks… but I’d like to take a few of mines and see how they compare. Can you estimate the depth of the sen marks? They look quite deep on some places.

    and who’s that saw being dissected on the background? are we hearing more from it?

    1. Thanks guys! I just today was able to photograph hammers, saw sen, spring clamps, and staple vise for the sen dai, as well as take detailed measurements of Marks fuigo from a saw maker friend of Yataiki, so I feel kind of crazy happy with all the cool knowledge I’ve gained recently. The technical refinements of the fuigo in particular are very important, and I took all of the measurements in centimeter so that I could draw up a set of plans for you Sebastian.

      I used a button micrometer the other day to measure saw plate thicknesses in preparation for trying the sen which is accurate to a thousandth of an inch, but it didn’t register any difference from the sen marks, which I suppose are on the order of microns and relate to the coarseness of the stone used to sharpen the sen. Though I was talking to mark today about the sen, and he mentioned that the final sen used is a heavily curved one that leaves shallow furrows which are then pushed down with miyagi, the burnishing tool.

      Great that you noticed the poor saw in the background, haha. I had mentioned that ryoba in an earlier post as having the worst nuke and twist I thought possible, and Mark was able to get the nuke out but it made the twist even worse. Then the twist came out, but the nuke was even worse again. So it basically got beat to death. Some poor bloke bought it on ebay for thirty bucks, and Mark quoted him fifty for the work with no guarantee’s, but probably has six-eight hours into it now to cut it down to a small rip kataba and remove enough of the nuke to get it flat. Very instructive for me to watch, poor saw, but at least its not a total loss.

      1. Thanks Gabe!

        Indeed, those furrows look quite deep, far beyond grit size. Almost like little engravings on the metal. They also look made a posteriori, only on the sides of the saw. Or is it? Looking forward to those plans. I will need to find another place to live though, to make a forge.

        Something just popped up in my mind. Have you seen mark flattening a saw, knowing when to stop but leaving small bumps and then using the sen to kind of lap it flat? Or this is just not common?

        1. Like little engravings, quite true. I suppose it could come down to the chip formation of the metal at the cutting edge. Have you seen close up video of metal cutting chip deformation? At the microscopic level it kind of tears out in front of the cutting edge as the force moves into the metal. I think perhaps that is the cause of the marks we see. The sen marks are pretty even across the saw, its probably an artifact of the light and my poor camera that makes it looks that way. I haven’t seen mark use sen as a normal part of metate, Its kind of important that the sen work is done before the teeth are set so that the plate will sit truly flat on the sen-dai. I’m working on a western panel saw (cast steel) that has really bad variation in thickness which evidently is quite uncommon for good panel saws, thinking of scraping the plate even. So it would require using sen on a saw with teeth already set, but Mark just says work with what you got, make it work. Also, the hammer strikes in hizumi shouldn’t be hard enough to leave noticeable bumps, only the ghost of the hammer strike from the polished surface of the face burnishing the saw plate. Though, even there I know Yataiki made some special “hammer finished” tamahagane nokogiri where he left the pebbled surface, and by all accounts they were extremely fine (and damn expensive).

          1. Next question, haha….

            Miyagi…. Are some details possible? Surface on the tool itself, the finish that it leaves on the steel, that sort of thing? I’ve pestered others for those sorts of details on these Yataiki saws but you need to have a certain level of background knowledge before the question makes sense.

          2. I have photos now of the burnisher for miyagi which I can send you, but if I can get get the sen-dai set up I’ll take some good photos of what the saw plate looks like during each process. The sen board should be keyaki, apparently anything of less than equal density will deflect under the pressure of the sen and cause problems, so I’m waiting to see if an old one can be found around here…The staple for the send-dai is supposed to be mounted into a large poured block of concrete, so anything I do is a bit red-neck. Mark also has stacks of fresh tempered blades with the right colour that have the teeth rough cut, just waiting for finish scraping, miyagi, and sharpening, ugh.

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