Yep.   One can add wedges to tenons.    Either the ones that go all the way through a joint, or ones that stop short of going through. 

 

 

Usually two wedges are used.     For the non-through joints, a little prep is needed.   The mortise needs to be back-cut, so that it looks like a dovetail slot in cross section.     Two saw kerfs are cut into the tenon, and two wedges made up that are just short of the full depth  of the tenon.   This is so that the wedges won't "bottom out" as the joint is closed up.    The mortise will act like a dovetail joint, in that once the joint is closed up, you can NOT pull it back apart.  So, make sure it all fits  BEFORE you bang things together.

 

 On the joint above, glue is an option.    The wedges will spread the end of the tenon into the dovetail shape.   You just barely start the wedge into the saw kerfs, and then drive the joint home.   Note: to take one of these apart, a saw is  your best option.     

 

On through tenon (like on doors) again two wedges are used.     Again, the saw kerfs are cut into the tenon.   Two wedges are driven in, AFTER the joint is clamped up.    Glue is an option here.    Just spread some on the wedges before you drive them home.   Again, cut the wedge after it is in.      In this case, wedges that are a little long, are just fine.     They can be trimmed after the glue has set.   Just saw them off, and sand flush.

 

Both of these style joints are meant to stay together.    If you need to take the joint apart later, use another type of joint.

It should also be mentioned that this joint is NOT for the faint of heart.

 

Steve explained it well except for the one pitfall of this joint, SPLITTING.

 

It is a VERY strong joint and it requires little to NO GLUE.

 

That being said, you should practice this method before final assembly.

 

Usually the kerf cut into the end of the tenon needs only 1/4 inch to start but the real secret is the length and thickness of the "Wedge" going in.

 

To thin and the joint doesn't "lock", too thick and the wedge doesn't penetrate.  Too long and the split will travel down the Tenon and out into the board, effectively ruining a good piece of wood.

 

It's the same principal as putting a wedge in a new handle to hold a hammer head.

 

Maybe a drawing steve and pics of one so our newbies can see what your saying?

I agree with Dragon. Some pics and drawings would be very helpful. I rememeber the first time I tried these, I ruined a really nice project piece. The split ran what seemed to be forever in the board.  As for the "NO GLUE" .. please tell me where you were the first time I tried these ???? LOL... I still use a little glue for saftey and habit. But as stated, these are very strong and very permanant joints.

 This weekend is my scheduled three days off,  I'll see about getting out to the shop for a little something to post here.   I think Roy Underhill had a show on Dovetails awhile back, and showed how to wedge a tenon inti a dovetail like joint.