Replies

1. 
   saschafer | Sep 24, 2007 09:34pm | #1

   I've seen this done. Visually, I think it works better (for reasons described below) if the tenons are approximately square in cross section.

   An important point that might be overlooked is that the wedge must always exert pressure along the direction of the grain in the mortised piece. So, for example, if it's a typical case where the grain in the sides runs vertically, the wedges must be oriented horizontally, "lengthwise" in the tenons. This can look odd if the tenons are of typical proportions, but is okay if they're square. Even so, it's tricky to make the saw cut in the central tenon(s) if there are more than two tenons involved on a side.

   Alternatively, I've seen square or nearly-square tenons with the wedge oriented diagonally, from corner to corner.

   -Steve

    

1. 
   Samson | Sep 24, 2007 09:38pm | #2

   Those points are very helpful.  Thank you.

2. 
   Lataxe | Sep 24, 2007 10:31pm | #3

   S,

   I'm doing some wedged tenons in a large oak trestle table at the moment so I noticed your post.  Like Steve, I have seen carcases (both bookshelves and tallboys) in which the shelves are afixed to the sides using square wedged tenons with one diagonal wedge.  They look very good, if you can keep them neat.  They look a bit like a fancy inlay of parallel rows of squares.

   The pieces I saw were all by one maker (whose name I can't recall) and he had obviously decided that one theme for them was "exposed joinery wherever possible".  The tops and bottoms were jointed to the sides with through houndstoth DTs; and the feet were similary cornered with exposed through DTs.  I think the stuff was in olive ash.

   I don't know if you've done wedgies before, if so forgive me telling you how to suck the egg.  :-)

   Chris Schwartz did some experiments that showed:

   * For greatest strength the wedges should flare out, trumpet-like, for only the last 1/2 to 1/3 of the mortise.  It makes the joint rather like a DT on a stalk.  This will surely make a very strong mechanical join - strong enough for shelves.  (You would need at lest two tenons - ie front and back of the shelf; but presumably could have as many as the depth of the carcass sides allow)?

   * Drilling a hole in the end of the split for the wedge does not prevent unwanted splitting inside the wedged joint but actually causes it.

   *  A split made with the grain of the tenon is stronger than a split made parallel to the sides of the tenon but across the grain (assuming the grain is not itself parallel to the tenon edges).  If you start the split in a symmetrical position, any "slope" in the grain-following wedge(s) is not visible in the finished joint.

   * White oak or another hard, fibrous springy timber makes the best wedges, least likely to crumble when you knock them home.  The contrast with the tenon end timber (if any) is a design feature appropriate to exposed joinery.  4 degree slopes for the wedges is about right in hardwoods.

   *  Wedges in rectangular tenons shouldn't be placed more than 1/8 inch away from the side of the tenon, as otherwise the outer edges of the tenon will be too hard to bend over when the wedge is knocked in (ie it won't knock in).  I think this will mean that diagonal wedges across a square tenon will need to be quite thin - ie less flare so less bend required of the thick triangular bits of the tenon either side of the wedge.

   Perhaps it's possible to put cross-wedges across both the diagonals of a square tenon (one of the wedges would need to be split into two)?

   Lataxe

1. 
   Samson | Sep 24, 2007 10:38pm | #4

   Thanks, L:

   I've done them:

   http://image57.webshots.com/757/2/77/59/2139277590032524639mtwjhk_ph.jpg

   and read the fine articles in WWing you reference.  I've not done them in a carcass situation, however.

   In the ones you have seen that you reference, did the gentleman have a string of such teneons spanning the carcass side?  I dould think this a bad idea as it would constrain wood movement too much.  I was thinking a couple in the middle, that would allow expansion to the front and back if required - riding in the dado.   

1. 
   saschafer | Sep 24, 2007 10:44pm | #6

   "In the ones you have seen that you reference, did the gentleman have a string of such teneons spanning the carcass side?  I dould think this a bad idea as it would constrain wood movement too much."

   If the side and shelf are of the same material, and the grain runs the "normal" way in both, then that's not an issue. They'll both move by the same amount, at the same rate.

   -Steve

    

1. 
   Samson | Sep 24, 2007 10:48pm | #7

   Of course!  I've gotten myself all turned around grainwise.  I think I had in my mind that sliding dovetails are often useful when you need to accommodate movement and sliding DT's are often seen in this scenario (shelf to carcass).  Sorry to be so thick.  And thanks for straightening me out. 

   Kind regards.

2. 
   saschafer | Sep 24, 2007 10:42pm | #5

   "Perhaps it's possible to put cross-wedges across both the diagonals of a square tenon (one of the wedges would need to be split into two)?"

   Why don't you try it and let us know how you make out. ;)

   -Steve (who has nightmares like that)

    

1. 
   Lataxe | Sep 24, 2007 10:57pm | #9

   Steve,

   I do have a not-so-secret ambition to make a tallboy in the style we have mentioned.  I was very impressed with the one I saw (must find the book with it in) despite it beng a rather modern piece (ie very clean lines, blond, sharp and rectilinear).  I can imagine that such joinery would not look so good on a more traditional piece.

   But perhaps there is some way to get that style into, say, a Mission or even Shaker thang.

   One day.

   Lataxe, still learning to saw, chisel and plane precisely (aerospace standard).

1. 
   saschafer | Sep 24, 2007 11:30pm | #12

   Oh, I wouldn't mind building something like that myself. It's your idea of crisscrossed wedges that scares me. (Although I have to admit that for a fleeting second it occurred to me as well, before I had a chance to purge the thought from my mind.)

   -Steve

    

3. 
   joinerswork | Sep 25, 2007 04:08am | #13

   Lataxe,

   Those crisscross wedges were regularly done on the ends of the legs of windsor  chairs made at a shop where I once worked.  And I've done something similar on the rectangular thru tenon on the handle of a mallet I made some time ago.  Instead of crisscrossing, the wedges are arranged thus: one longitudinally, driven just tightly enough to spread the tenon into the flared sides of the mortise (but not enough to split the mallet head!).  It is intersected by two crosswise wedges near the ends of the tenon, flaring them into the ends of the mortise.  Once the first wedge is driven, a tap with a chisel splits the wedge, and makes room to enter the opposing wedge into its (previously sawn) slot.

   Ray

   
3. 
   JohnWW | Sep 24, 2007 10:49pm | #8

   If appearance isn't a concern, probably because the outside of the carcase won't be visible, then a simple screwed together butt joint, possibly with a shallow dado for the shelf ends, would be a fast and solid solution.

   Shallow tenons are too short for an effective wedged joint and a tenon only in the center third of the shelf won't hold the shelf tight to the sides at the front and back edges. Two or three tenons over the width of the shelf would be more effective.

   John White
   Yestermorrow School, Waitsfield, Vermont
   FWW Experts column contributor

   
   

   ---

   Edited 9/24/2007 4:05 pm ET by JohnWW

1. 
   Samson | Sep 24, 2007 10:58pm | #10

   Thanks, John.  I'm loathe to use screws for irrational reasons. 

   You said : Shallow tenons are too short for an effective wedged joint

   Doesn't this make it a non-starter from the get go?  It was the cause for my initial hestitation and OP.  Then again, others here have seen it done (though perhaps foolish and ineffectually?). 

1. 
   Samson | Sep 24, 2007 11:09pm | #11

   Google came up with this from a competing mag, FWIW:

   http://www.woodworkersjournal.com/articles/37-3.jpg

   http://www.woodworkersjournal.com/articles/37-2.jpg