A couple of issues back, Woodworking magazine had an interesting article about wedge tenoning. The author tried several ways to wedge – saw kerf, saw-kerf stopped by drill hole, and chisel if I recall correctly – and then cut them open to show the results.
As I’ve never had occasion to try wedge tenoning, and needed a new saw bench, I undertook a saw bench project (using hard maple) also included in the same issue which calls for the stretchers between the 2 1/2 inch square legs to be wedge tenoned in place.
The author of the wedging article was surprised to find that some of the best results came from using a chisel to split the end of the tenon for insertion of the wedge. Hence, I decided to try this method.
Well it worked very well on two, well enough and one, and not so good on the fourth. The problem arose when the chisel splitting method combined with the grain in that particular board, left a less than ideal avenue for the wedge. I drew a diagram to clarify – the red line is the path you hope for and the one I got seven out of eight times – the blue is the bad result I got once. I was still able to wedge it, but in the process, the broken edge of the tenon ended up a 1/16th below the leg surface (no issue in a saw bench, but problematic for a trestle table project or the like.
I report this for your consideration, input, and to let you know what I’d do different next time:
1. I’d use a Dozuki to saw a thin kerf path for the wedge and thereby gain some ability to direct and ensure the path (insurance against unpredictable grain).
2. I used walnut wedges to contrast with the maple. The walnut was a little soft for the abuse wedges can take. One split up the middle half way in – no effect on result, but suggested that if possible, I should use the strongest possible wood for the wedges. Another reason to use strong wood for the wedges is that you would not want a wedge to break off before being driven home fully as might happen with a quirk of grain in the softer hardwood wedge or a slightly errant mallet blow. This latter scenario could always be addressed with a second wedge, but again the joint might look a little less precise and pretty.
For what it’s worth.
Replies
You were right to use a Dozuki saw to make the wedge channel. It gives the wedge a difined starting point and allows the tendon to split naturally. Using a harder wood for wedge is also correct. Then when the tendon and wedge are sanded flush, the result is barely notiseable and you have a uniform finish on the joint.
Samson,
I read that article too and it was a bit of a revelation. (A thorough chap is Mr Schwartz).
In the past I always put that drill hole in the end of the wedge-cut "to stop the wedge-cut travelling too far". In fact, it seems a drill hole can actually cause the cut to break off a tenon shoulder within the joint. Ah ha - it suddenly becomes obvious how that can happen when you see it!
Having worked a bit with green wood, I know how determindly a starter-split will want to follow the grain. With cabinetmaking, you have already sawn the timber and the grain, as you mention, may be travelling here and there - not parallel to the workpiece edges, necessarily. So I think you're right to avoid the chisel-splitting method for making the wedge-opening, as this is essentially riving the split, which will then follow the grain where it will....
Lataxe
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