Replies

1. 
   KeithNewton | Jan 10, 2005 04:40pm | #1

   Goota meetcha back. I don't have time to write the book here to answer this question, but I would like to suggest that you try to find one and read it.
   A few general guidelines though would be.
   Always use a harder wood for the wedge.
   Position the wedge near enough to the edge for the planned force to actually meet the expected deflection in the tenon.
   I know there is a law in physics and a mathematical formula which states what force can be expected for the spreading force for each unit of force applied to the butt of the wedge - the friction on the sides of the long faces of the wedge. I don't know if X force on a 4 degree wedge gives twice the spreading force as an 8 degree wedge or if it is squared or even cubed, but it will be more.
   If you make the wedge angle too narrow, it will collapse from the drive in force.
   Some glue will act like a lubricant and cause the spreading force to allow the wedge to creep or even spit the wedge back out.
   Always make samples and test what you are asking the wood to do.
   You can learn more from making samples and doing your own quality control than just doing something and hope that it works.:

2. 
   joinerswork | Jan 10, 2005 04:41pm | #2

   Hello John,

   As you have pointed out, there are so many variables that it is difficult to give any hard and fast rules for bling wedging.  It's best to do a trial run on scrap stock, to test the set up for depth of mortise, length of tenon, and degree of flare of the wedge. This will vary for different species as to their hardness, and consequently, the amount they will compress during assembly. Trial and error, make the errors on scrap!

   Regards,

   Ray

1. 
   mitch | Jan 10, 2005 06:53pm | #3

   i kicked this around with a neighbor a few years back who was building a headboard and after a little trial and error we basically determined that the 'volume' of the wedge had to be pretty much exactly equal to, or ever so slightly less than the 'volume' allowed for it by undercutting/flaring the mortise for expansion of the tenon plus the kerf the wedge goes into.

   i really don't remember much of the other particulars such as proportions, how big to make the wedge(s), length or width of slot kerfs (DO drill a round hole at the end to prevent splitting), etc, only that one shouldn't try to factor in any significant wood compression on any part- the risk of being unable to completely close the joint was too great (not to mention the inability to take it back apart).  he was using some sort of titebond and figured that would tend to swell the wood initially anyway.

   hope this helps...

   m

    

3. 
   Peter36 | Jan 10, 2005 08:50pm | #4

   Hi John and nice to meet you too. I make my wedged tenons blind or through a little differently. I cut them as illustrated below instead of cutting parallel to the side of the tenon. I do this because when cutting parallel you are somewhat limited by the bending forces on the outside piece. Doing it this way you can make the outside piece of the tenon whatever size you want. As long as all the pieces have glue applied then it does not matter if the fragile ouside piece breaks off [I cut mine to just short of cutting it all the way off.] because the glue joint is stronger than the wood anyways. Good luck.