Replies

1. 
   JohnWW | Dec 30, 2006 01:08am | #1

   I looked at that illustration and read the description when I first got that issue and I'm also clueless as to why the haunched joint is supposedly stronger than the simple tenon shown above it. 

   I studied structural engineering in college, have built several timber frames, and regularly analyze complex furniture joints, so I'm pretty sure that I'm correct in feeling that something is not right in this. 

   My guess is that the original tenons were actually half high tenons, basically like the longer upper half of the haunched tenon in the lower picture. If that were the case, then adding a haunch would add some vertical load strength to the joint and would also make the joint better at resisting the beam rotating about its long axis.  The single pin shown in the upper picture would also suggest that the original tenon was only half high, since a full width tenon would have had the single pin centered or even more likely, two pins, one high and one low, probably on a diagonal line. 

   Also, if the original mortise was for a half high tenon, then the mortise could be recut for the haunch, which is what was implied in the text on page 38.  If the original mortise were full sized, as shown in the upper drawing, it couldn't be made smaller to fit the haunched version.

   All in all, I suspect that this was a case of miscommunication between the author, the editor, the art director, and finally the illustrator.

   John White 

1. 
   GaryBowen | Dec 30, 2006 01:16am | #2

   Thank you.

    

   Gary