Replies

1. 
   eddiefromAustralia | Dec 10, 2003 02:04am | #1

   Creekwood,

   I'd use a castellated tenon.

   xxxxxxxxxxxxxxxxxx
                                 x
                                 x
                                 x
                     xxxxxxxx
                     x
                     x
                     xxxxxxxx
                                 x
                                 x
                                 x
   xxxxxxxxxxxxxxxxxx

   cheers,

   eddie

2. 
   JohnWW | Dec 10, 2003 04:06am | #2

   Creekwood,

   Splitting the tenon won't do anything to compensate for the expansion and contraction of the tenoned board, split tenon or not, if the entire tenon is glued in, or solidly pinned near the outer ends of the tenon, there will be stress on the board that may cause it to split if it dries out and shrinks.  On narrower boards the stress usually isn't enough to create a split but starting around six inches the stress starts to become worrisome. 

   The primary reason for splitting a tenon is that it makes the sides of the mortise stronger and less likely to flare out from wood movement or tear out if badly overstressed.  The secondary advantage is that there is less wood to chisel out, an attractive feature when mortises are cut entirely by hand.

   The way to avoid potential splitting from wood movement is to only glue about a third of the tenon surface leaving the remainder to float in the mortise.  Usually the part that is glued is along the more critical edge of the tenoned board, the upper edge of a table apron for instance, so that the board continues to support the table top.  An alternative method, or one that can be used in addition to the glue, is to pin the tenon solidly at one point with all additional pins put through elongated holes in the tenon to allow for expansion and contraction. 

   A final alternative using pins, that is a little less fussy but usually strong enough for most applications, is to put two fixed pins in through the tenon near the center, spaced about a third of the width of the tenon apart, leaving the two ends of the tenon to float. This joint can be further strenthened by putting glue on the center area of the tenon cheeks between the two pins.  This can be done with a straight mortise or a split one which would be sturdier.

   Issue number 165 of Fine Woodworking, October of 2003, has a good article on controlling for wood movement in mortise and tenon joinery.

   John W.

   
   

   ---

   Edited 12/14/2003 7:35:14 PM ET by JohnW