Replies

1. 
   ErnieConover | Apr 13, 2006 01:58pm | #1

   This type of locking wedge tenon are tricky to cut because it is easy to make the mortise too long which will negate the tenon locking up. The first consideration is leaving enough relish. This is a term from timber framing which refers to having enough wood beyond a cross hole to take the load rather than split along the grain. From your description, you have enough.

   I usually make the joint by machine then use a chisel to put the 5 degree taper in the mortise to match the wedge. You want to figure the joint so that the wedge just seats as it will seat lower with time. This requires cutting the mortise to minimum size then hand fitting with the afore mention mortise chisel.

   One good thing is you can always make a wider wedge if it starts to seat too low. Wedges work very well and were the cotter key of the 18th Century.

   With best regards,
   Ernie Conover

1. 
   LakelandDave | Apr 13, 2006 04:00pm | #2

   Thanks Ernie. That's helpful information. Another aspect of the tenons I am curious about is how you go about proportioning the amount of tenon 'outside' the wedges in relationship to the amount between the wedges. In other words, would 1/4" to 3/8" be about the right thickness for that outer portion on a tenon that has an overall width of say 2-1/2"?

1. 
   ErnieConover | Apr 13, 2006 04:20pm | #3

   A rule of thumb for mortis and tenon joints between equal weight stock (such as in face frames) is that the width of the mortise should be one-third of the thickness of the stock. (On a face frame of 3/4" thick stock the ideal mortise would be 1/4" wide. Following this line of reasoning your two mortises should remove 1/3 of the height of the tenon. So one-third of your 2-1/2 height would be a little less than 7/8" Half of this would be 7/16". As this is a rule of thumb and you can cheat a good deal you could go with either 3/8" or 1/2" mortises very nicely.With best regards,
   Ernie Conover

1. 
   LakelandDave | Apr 13, 2006 06:16pm | #4

   Ernie - I'm afraid I didn't express myself well. I'll attempt to attach a file to this post (Tenon2.bmp) that should help you understand my question. The sketch shows a tenon on the workbench stretcher. In case the dimensions aren't clear, the stretcher is 1-3/4" x 4"; the tenon is 1" wide x 3-1/4" high x 3" deep. My question related to how much wood there should be to the outside of the wedges - as opposed to the center portion. On the sketch, I've shown the outside pieces 1/2" high and the center as 1-1/8". I've shown a 3/8" hole, 2-1/2" back from the end of the tenon - with the narrow end of the slot 1/4" high - and about 7/16" at the end of the tenon. I've shown the taper cut on the middle section, but that could be on the outer sections if that would be better. Please make any corrections or suggestions you feel would help.Thanks again - Dave Owen

   
1. 
   ErnieConover | Apr 13, 2006 10:22pm | #5

   I am sorry for not picking up on the gist of what you were doing. Workbenches are often held together with locking wedges that allow the user to disassemble for moving and such.You have the whole thing doped out just right. The "thirds rule still works. Most important is the height of the tenon vs the height of the mortise should be within 1/16"--or less. The cross hole at the end of the tapered kerf helps greatly to prevent stress from running beyond the shoulder. Unless you are using contrasting woods you can actually just back saw about 1/4" form each edge Put some glue on the wedge and drive it home. Most entry and interior doors were made this way up until the lathe 19th Century. The mortises ran all the way through the stiles and were wedged from the outside. No glue was used and getting one of these doors apart is a task in itself. Post a photo when it is done.With best regards,
   Ernie Conover

2. 
   LakelandDave | Apr 14, 2006 12:10am | #6

   Thanks so much, Ernie! For those of us who are inexperienced, having a knowledgeable source of information is a tremendous help. I will, indeed, post a picture when the workbench is finished - but at 75, things don't move ahead as quickly as they once did.Dave Owen

3. 
   ErnieConover | Apr 14, 2006 02:38am | #7

   Age and cunning will beat youth and enthusiasm any day!With best regards,
   Ernie

2. 
   Panzer | Dec 24, 2007 11:31pm | #8

   I am also building the essential workbench and had trouble with the dowel joints in terms of how much offset to allow.  I allowed very little but the dowels broke off when I tried to pound them in so I just drilled them through.  What was your experience?  Any other lessons learned?

1. 
   ErnieConover | Dec 26, 2007 04:42pm | #9

   Draw bore pinning of mortise and tenon joinery is commonly used in timber frame construction. The draw is usually 1/16". That is the holes are purposely drilled out of alignment with each other by this amount. The peg that is then driven is whittled with a draw knife from riven stock. The pin has a long taper so that it can accommodate the offset and then "draw" the joint into tension. The reason for the draw bore is to try to ameliorate the effects of the shrinking of the green wood used in timber frame construction as the frame dries. It is doubtful that draw bore does much in dry wood cabinet work. At the scale of your workbench the draw could only be about l/32" and the dowel would have to have a tapered point to not have the problem you encountered. The main advantage of a draw in this case would be to hold the joint solidly together while the glue dries, negating the need for clamps. Given the rigmarole of draw boring and the simplicity of clamping, I would probably elect to do the latter. All this is to say that your project will not suffer from drilling in alignment. With best regards,
   Ernie Conover

   Edited 12/26/2007 8:43 am ET by ErnieConover

1. 
   Panzer | Dec 26, 2007 07:43pm | #10

   Thanks, your reply confirms what I was thinking.

    

    

1. 
   ErnieConover | Dec 26, 2007 08:05pm | #11

   You are most welcome. ERC