Project Mayhem #2.....
KOSHIKAKE KAMATSUGI (STEPPED GOOSE NECK SPLICE)
Got two short beams but you'd rather have one long one? Here we go. GabeD added some basic proportions to the illustration to make things easier for us......now if only he would give me a sashigane.....
I cut my version of this stepped, goose-neck splice using an old chunk of 4x4 that I had rescued from the dump. All told, my time in was 3.5 hours, one shot, no trial fitting, and I made the thing too darn tight. This is never coming apart (not necessarily a good thing, too tight). The bulk of the time was in excavating the recessed areas and making the inner faces as flush, plumb, and true as possible. The finished joint looks cool, is decently strong, and was very fun to cut.
Thanks Gabe, great choice!
Gabe gave us the essential proportions for the joint, so converting that information into the proper size for my timber took some thinking on my part (sometimes an iffy proposition). The proportion system makes things quite simple, and the only thing that really gave me pause was that of the angled slope of the goose-neck /hammerhead part. The slope is determined using the standardized width of the sashigane ( the Japanese carpenters square), but not actually having one, I first had to do some research (it is 15mm BTW). Then had to do a bunch of fidling using my ruler, drawing and measuring, never a good thing.
Note to self.....get a sashigane! I keep hoping to find one here in Hilo, but haven't had any luck so far.
I square the stock, plane things smooth so that I can better see my layout, then start drawing.
This timber is large enough to use a proper centerline layout method, something that is really growing on me. With any stock that is less than perfectly square and of uneven thickness, centerline is my new way. Slow learner, I guess.
I grab a marking gauge, set it to something close to half the timber width, then make a mark.
I strike a second mark from the opposite face.
In this example, my gauge was set too close to the halfway, so my two marks kind of smooshed together, but the result is close enough to the true center. Now I can strike a line the length of the joint, to use as my origination point for laying out the joint.
I started out squaring off lines using a regular carpenters framing square, but the huge, awful thing was way more trouble than help. A machinists try-square was of greater assistance. I layed out both halves of the joint on the same piece of wood, just separated by a 1/4" waste portion.
Note to self.....get a sashigane!
On the positive side, for this joint I inked the lines using a 0.2mm pen and it worked wonderfully. Not as cool as using the bamboo pen, but far better than the mechanical pencil that I have always used in the past. I never would've thought that I would be cutting to an accuracy of fractions of a millimeter, but here we are.
Layout.....1 hour, half that being wasted by researching sashigane and my slower layout, on account of its lack.
I cut every perpendicular line possible, while the stock was still full length. Easier to hold on to that way. Sawing all of the crosscuts while the timber is still whole, as opposed to ripping some of the waste first, means that I do nearly twice as much sawing this way. I use my plain-Jane Z-saw 265 kataba, nothing fancy. A decent construct grade saw.
I'm finding that if I don't use any clamps to hold the piece being sawed, if I rely on gravity, a screw/stop on my bench and just hold the material with my off hand, it forces me to saw in a very neutral and controlled manner.
More accurate cuts are the result, as well as longer saw life, I suspect. After the two pieces are separated, I rip the other lines, trying to maintain accuracy. I am trying to only saw to half the thickness of the line, leaving nothing to pare or finish.
The cheeks of the mortice are cut using the same saw, but a rip tooth would've been much faster here. I wrap a piece of tape on my auger bit to set the depth, then bore out the ends of the mortice to make the excavating easier.
My favorite beater chisel, doing its thing. I need to fix another stop block to my bench for this sort of thing, it being hard duty for any clamp. It feels like 1/2 the force is absorbed by the movement of the workpiece.
This sidewall of the mortice is tolerably square......
But this side has too much undercut for my liking. Sloppy work.
And another little error shows its head. I mis-measured the goose-neck /hammerhead part. The mortice is correct, but the shoulder of the male portion is 5mm off.
Easily rectified. Given a second chance, I cut this line to a very slight taper which will help draw the joint tighter.
The moment of truth. I used a block of wood and my small ball-pein hammer (not the heavy sucker) to drive the joint home.
It is very tight, so there will be no second chance for this guy.
A few gaps, but not horrible.
The underside of the joint shows the worst. The tongue is just a hair fat of the line.
So, a great practice joint, fun to cut, too. By deciding to do as much cutting as I could, right from the get-go, I had more sawing to do, but less drawing and extending of lines. Possibly that helped my accuracy, I'm not sure. Sawing is fun, so I'm happy with that decision.
I am less than thrilled with my excavation of the goose-neck mortice. The level of undercut at the sides was excessive, and the depth of the mortice varied a bit as well. Gabe used a sliding bevel gauge to measure depth and angle when he cut his, and that seems a great use for a tool that most of us have. I was actually considering making a dedicated mortice depth tool but this day found me in more of a hammer/chisel/hit stuff mood, and for some reason the sliding bevel gauge didn't even occur to me, haha.
Finally, I cut this joint too tight. With my current level of skill, it would be better had I allowed for at least one trial fitting. I got lucky, thought the fit isn't quite as "perfect" as I would like.
Time to consider the next challenge, eh?
Maybe we save this one for later.