Replies

1. 
   Frank Vucolo | Oct 07, 2009 03:38am | #1

   Don,

   If you fit the apron flush to the leg, using a 3/8 tenon, the remaining material on the wall of the mortise will only be 3/16. The added tenon strength would be offset by the weak mortise.

   I suppose if you offset the apron there would be nothing wrong with a 3/8 tenon.

   Frank

2. 
   hammer1 | Oct 07, 2009 04:14am | #2

   Go for it, Don.

   Beat it to fit / Paint it to match

3. 
   Senomozi | Oct 07, 2009 04:01pm | #3

   You already mention the only disadvantage I could think of: frail leg. Something that can be easily fixed with an offset apron or an offset tenon (different cheek thicknesses).

   While answering another post I came across the joinery shootout article from Jan/Feb 2009. I had read this article but had forgotten that they tested both 1/4" and 3/8" mortise and tenons. The 3/8" version was about twice as strong as the 1/4".

4. 
   joinerswork | Oct 07, 2009 04:32pm | #4

   Don,

   No disadvantage at all.  As long as the mortise is held back from the outside edge of the leg sufficiently, you'll be all right.  The "rule" of 1/3ds applies mainly to joints wherein both members are the same thickness--think door frames.  When one member is thicker than the other, if the thicker (mortised) member is not compromised by the removal of (more than 1/3 of) the wood for the mortise, making the tenon thicker does nothing to weaken the tenon half of the joint.  One can even make the tenon "barefaced" (no shoulder at all) on the back side of the apron, allowing for a 3/8" tenon with a 3/8" shoulder on the front of a 3/4" apron.  This will allow a 3/8" (or more if the leg is left proud of the apron) setback for the mortise.

   A point frequently overlooked in seeking to create a strong joint in a table apron is in making the tenons overly long.  This is sometimes done to the extreme where they actually intersect inside the leg.  While this may increase the glue area of the tenon-to-mortise interface, the removal of so much wood from the top of the leg leaves it a mere shell, and dragging the table across an uneven, or carpeted floor, may cause the leg to break apart at the joint.  A subsantantial haunch at the top of the tenon, adds strength to the leg by leaving a web of wood that effectively knits the top of the leg together.  And, a wide (over 5") apron ought to have its tenon divided or split in two, so that the twin mortises in the leg have a strengthening web between them.

   Ray

    

1. 
   dull tool | Oct 08, 2009 01:25am | #5

   Don, with 3/4 stock I have had good luck making 5/16" tenons.

1. 
   DonStephan | Oct 08, 2009 03:52am | #6

   Thanks for the responses.  Should have mentioned that the apron would be set back from the front of the leg about 1/8"!

   To date my mortising chisel and bit sets (nor my mortising chisels) don't include 5/16", hence my choice between 1/4" and 3/8" for the apron. 

   If I understand the suggestions, I'll aim to have a minimum outside wall thickness of 1/4" for "typical" mortise and tenon joints.  And the 1/3-1/3-1/3 guideline makes so much more sense if applied to mortise stock than to tenon stock.

5. 
   ILoveMartinis | Oct 08, 2009 02:38pm | #7

   What kind of table are you building?  Joinery should work as a system - four apron to leg m&t joints will be pretty strong even if you use 1/4" tenons.  That said, if the legs are beefy, indicating a larger table meant for more robust use, then by all means increase the tenon thickness.