wood movement with wedged tenons and rabbets
Howdy,
I’m fixing one my first woodworking projects and adding angled legs with the hope of doing through wedged tenons into the table. I have two potential issues but first, here’s a description of the side table it self:
– it’s flat sawn red oak (11/16th of an inch) with a 14 inch glued up panel on the top and bottom and two 4 inch sides
– orientation of the grain is so that the face of the piece is the end grain so the grain would expand side ways. so kind of the opposite wood direction of a solid wood cabinet carcass
– I originally had it glued up with miters but took that apart
– there’s no drawer in the middle it’s just open
Here’re the two potential issues:
– I plan to Rabbet the sides since I prefer that look and miters are hard (the original one had crazy gaps)
– I plan to mortise the bottom panel for each leg and add a wedged tenon. (tenon should be about an inch or so)
Do you think wood movement will be an issue with the both?
Replies
I would not glue 14" along the grain to 14" across the grain, which I think is what you are suggesting with the rabbets. It would probably be okay if the MC never changed seasonally or if the MC change was very small. The joint will likely fail if the MC changes more than a few precent.
There are fasteners that allow movement for connecting pieces with different grain orientations. Sometimes slots are used with screws to allow the wood to move. Sometimes the wood is cut and glued in a way to allow movement (look up "breadboard end").
I can't tell what you are saying with the grain on the face. It sounds like the crosscut face of the wood is at the top and bottom (the wood grain runs up and down), like a butcher block surface. If so, consider that the wedged tenon might split the wood. Also, consider the strength of the top if someone pushed down on it hard. A tenon is so small that a lot of stress will not develop in the glueline with normal MC changes. Do make the mortises so that end grain is not being glued. Most of the glued area in the joint should be side grain in both the mortise and tenon.
I can confirm for all panels the grain runs top to bottom as you mentioned in your parenthesis. That means the top and sides run in the same directions for the Rabbet. so not necessarily glued across the grain but with it so for example, the top panel would move side to side and the side panel would go up and down, though not as much since the side panels are 4 inches in width at most.
I get your point about the wedged tenon. There'll also be a stretcher to connect the two legs.
Just so we know what we're talking about... this is what I took away from your description... is it correct? We'll need to know more about the legs' size, shape, and position. A sketch of the whole table would be great.
That sketch is spot on. including my own.
Wood movement is so affected by the local climate. That said it looks to me like you've designed this so all movement works to spread joints apart. The sides will expand vertically, pushing the rabbet apart in that direction, albeit not very much. The top and bottom will expand more sideways, forcing that apart in that direction. When it shrinks, it will do the opposite. Over time, I would think you risk having the joints fail. I don't see an issue with the wedged tenons for the legs.
One easy remedy would be to forget the rabbet. Use dowels or floating tenons to attach the sides to the top and bottom. The larger top and bottom can expand on their own. The sides won't move enough to worry about it.
You could also miter and spline the pieces, but that could be tricky.
Maybe in your neck of the woods it would work out as designed if the seasonal variation in humidity and temp isn't that much.