Sage-Kama Desk – Build 1

At last we’re on to the build process for the desk (the design posts are available here 1, 2、 3). Up to this point I’ve been somewhat generically calling this Desk 3.0, but I thought it deserved a more substantial name, so I’ve renamed it after the joinery that initially inspired the concept, that being the wedged half-dovetail joints that will be used to secure the legs. I used these joints extensively on the heavy duty shelves that I built a while back, and initially was introduced to them on a project with Somakosha. The technical name for these joints are kata-sage-ari (片下げ蟻), but a more colloquial name is sage-kama (下げ鎌). The kanji for kama refers to a sickle, the hooked shaped of which is a reference to this joints half-dovetail.

Anyhow, below is the layout on the legs for the sage-kama joinery. The round marks designate the parts of the mortise that I can cut straight through, while the double lines designate the parts of the mortise that slope. Finally the haunched part of the mortise is marked with a series of dashes/dots around it’s perimeter and it’s depth, 8mm.

The first step for cutting these joints was to rough cut the mortises using a hollow chisel mortiser. Since these are through mortises, I cut half-way in from one face, flipped the piece and finished the cut from the opposite face.

From there I used a chisel, chopping and splitting my layout lines to form a clean reference surface for running a bearing bit in a trimmer.

Here’s the mortise after running the trimmer to clean out the interior. The trimmer bit leave the corners of the joint rounded, but all of that will be removed when trimming the sloped ends to accommodate the wedge and half-dovetail.

Here is the start of that process. I chop with a chisel to clear out the waste, while aiming the chisel for the end of the mortise on the opposite side.

After a bit more paring and fine tuning the finished slope looks like this.

The last step for these mortises was to cut out the shallow 8mm deep haunches, which I did using a trimmer to clear the waste and chisels to pare to the line.

From there I put the legs on the lathe to turn them round. I plugged the mortises with some scrap hinoki to prevent the sides of the mortise from blowing out when turning. The legs are 40 mm in diameter and about 720 mm long (D1.57″ x 28.34″). When I initially milled and joined the legs I brought them all down to 40 mm square, which makes it pretty easy to turn them to a consistent diameter by turning them just until they become perfectly round. The lower half of each leg has a slight taper which I cut mainly by eye, using a caliper to measure a few points to keep the shape more or less consistent for each leg.

After turning I planed each leg with a kanna, leaving a clean, lightly faceted surface.

With the legs done I moved on to the layout for the cross braces that support the top.

These pieces will get a round cutout as well as a pair of flared mortises on each end, to accommodate the wedged tenons coming from the long stretchers. The layout for the okuri-yose-ari, segmented dovetail joinery hasn’t been layed out at this point.

And then it was on to more mortising. I roughed out the mortises again using a hollow chisel mortiser, followed by some paring with the aid of a jig to cut a consistent flare to the mortises.

How much to flare wedged tenons/mortises is always a question that pops up when laying out these joints. And it seems like there’s plenty of variation from carpenter to carpenter. One of my teachers would flare the mortises no more than a pencil width, for a really minimal taper. I’ve seen other reference to flaring the mortise using a ratio like 1:6, similar to laying out dovetails. Personally I’ve started to determine the angle by eye, holding a sliding bevel up to the piece I’m working on and adjusting it until it seems about right. I’m guessing I end up somewhere in the 1:10 ratio range most of the time. Truth be told, after cutting these mortises, I started to worry that I flared them too much, especially since the material is pretty tough white oak. But having now just assembled these joints, I can definitively say that everything worked out. It’s a testament to the flexibility of wood I guess.

After cutting all of the mortises in both the long stretchers and end cross beams, I moved onto cutting the tenons that will fit those mortises. Since the intermediate cross pieces are short I was able to cut the tenons for those pieces on the table saw, but the long stretchers being much more unwieldy and hard to safely cut on the tablesaw, I decided to do by hand. In the picture below the intermediate cross pieces are sitting on top of the long stretchers.

Here are a set of tenons on the long stretchers. I used a Nakaya Eaks 0.2mm rip saw for ripping the tenons. It was my first time using a rip version of this saw, and it cut beautifully. The kerf is so thin that you can barely make out the cuts in the photo below. I find a really fine saw like this allows me to get closer to the line and where I want to cut. The kerf is so fine and clean that you have a lot of clarity over where the cut is going.

After ripping the tenon cheeks with the hand saw I cut the shoulders on the table saw, and then knocked out the waste with a combination of a trimmer router and chisels.

Last step for the tenons was to cut the kerfs for the wedges. I once again used the thin Nakaya rip saw for this, and simply eye-balled the cut, trying to cut at a decent angle. Angling the cut helps to prevent the tenon from splitting.

And lastly a quick test fit to make sure everything was coming together as planned.

Well that’s all for now. Stay tuned for the next phase of the build next week. Thanks for reading.