Yeah but as well, doug fir knots are not all that big and not all that hard either, sometimes loaded with sap. Chipping out a chunk of a knot from the inside side of a mortise should be the real concern, and unsightly. I would avoid knots in the tenons as well for the same reason, loss of strength.
other side?
-------------------- Steve Jensen Abbotsford B.C. snipped-for-privacy@canada.mortise.com chopping out the mortise. BBS'ing since 1982 at 300 bps. Surfing along at 19200 bps since 95. WW'ing since 1985 LV Cust #4114
Nothing catchy to say, well maybe..... WAKE UP - There are no GODs you fools!
Sorry, it's a friend's site and I posted the link because it's what I had, not the best illustration of the joint.
In lots of wedged M&T joints you have to insert the wedge from the outside end of the tenoned member, but for these you do it from the inside. If your primary goal is to make a "box frame" where the wedges are inserted from "inside", then the wedged half dovetail is a useful choice.
The basic joint begins with a M&T Then the lower edge is cut at an angle (both parts) to make half of a dovetail. This dovetail has a "steep" angle on it, I think we used 1:6 for these hardwood joints.
Above the tenon the mortice upper face is also slanted at an angle, but _not_ the tenon. This angle is shallow compared to the other (important!), maybe 1:8 or 1:10 for this bench. It's also cut in the "opposite" way to how you might expect a dovetail. Matching locking wedges are cut at this same angle. There's wood removed right through the depth of the mortice so that the locking wedge protrudes through both sides, and also so that there's enough spare height with the wedges out to allow the joint to be assembled.
The joint now fits together quite loosely as the tenon is free to move up and down. Don't assemble it by titing the tenoned member, or you'll find that you can assemble one, but not two - make those wedges thick enough to give space. Once assembled, drive in the wedges to lock it. As always, drive wedges with a light hammer, not a maller (you can hear when they bottom out more easily)
The racking strength of the joint depends crucialy on having a different wedge angle for the "dovetail" and for the wedge. So long as the wedge is much more shallow, then it's possible to get a good lock on the dovetail part.
This is a fairly common joint in Japanese joinery as the shitage-kama and has aspects to recommend it for wider use. If you can cut the angled mortices (a wedge on the morticer table is all you need) then it's an easy joint.
It's not in Kiyosi Seike, it is illustrated in Graubner (not a great drawing though) and it's described in Sato & Nakahara . All three of these books are worth having (Graubner is OOP and S/H prices are insane
- Nakahara is a better book anyway)
In Japanese work (and Japanese timber) the angle for the "dovetail" part is typically steep and the other side of the mortice is cut square, with a very shallow peg (typical of Japanese timber-framing work). This is a good joint for house carpentry, but it doesn't have the resistance against moving under racking stresses that it does if you cut with two angles and a less steep dovetail.
It's also cut in Japan as a blind mortice (hard work to cut) or with the dovetail only cut on half the tenon's length.
The thought of a different wedge angle came to me this morning...since the "weakness" I saw in this joint seemed to be the wedge and tenon coming out at the same angle. The wedge angle makes more sense.
I can see this joint being a very good choice for something to be knocked down.
Thanks for the excellent answer.
-------------------- Steve Jensen Abbotsford B.C. snipped-for-privacy@canada.mortise.com chopping out the mortise. BBS'ing since 1982 at 300 bps. Surfing along at 19200 bps since 95. WW'ing since 1985 LV Cust #4114
Nothing catchy to say, well maybe..... WAKE UP - There are no GODs you fools!
I notice that the joints and drawers took a long time to make. How long did it take to get the bench 'covered in crap'? :o)
BTW, interesting joint and links.
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