Replies

1. 
   TomT226 | May 17, 2007 03:37am | #1

   For 4/4 stock, IMHO, 1" is plenty.  Check the "Bit Choice for Drilling Mortises" for more information on how to do it the easy way.

    

2. 
   ring | May 17, 2007 06:53am | #2

   I don't know of a rule of thumb; it depends on the application.  In table legs I prefer to make the mortises as deep as they can be - before they bump into each other, that is.  So in your case that depends on where the apron is placed in relation to the legs.  If it's right in the middle of the 3 5/8" leg then my gut says you've got a mortise depth of about 1 1/4".  Draw the cross-section to scale and see for yourself.

   BTW you can easily get straight-cut router bits 1/2" diameter x 2" long.

    

   David Ring

   http://www.touchwood.co.il/?id=1&lang=e

1. 
   studly | May 18, 2007 02:36am | #10

    

    

    

   Hi Dave  I'm looking for an upcut spiral bit . You are correct , 2" cutting bits are availible.

    

    

    

    

    

    

    

    

3. 
   joinerswork | May 17, 2007 03:51pm | #3

   stud,

   I like a 1" tenon length for most furniture work.  It provides ample glue area for most applications, without excessively weakening the mortised member.  Plus it is easy to calculate the length of stock when preparing a cut list: add 2" to the between-tenon measurement.  One shop I worked in used 7/8" tenon length for most of their work.  3/4" feels a little skimpy to me somehow, (especially if the joint will be pinned) unless the stock being mortised won't allow for longer.

   Some exceptions: heavy panelled door frames, where an extra long, even a through tenon doesn't hurt; nesting tables, with dainty little tapered legs which would be weakened by deep mortises; Phyfe-type sabre-leg chairs, where the thickness of the chair's sides won't allow for a long tenon.

   Regards,

   Ray

1. 
   9619 | May 17, 2007 09:46pm | #7

   Ray,
   Stud asked about mortise depth.
   You responded with recommended tenon length.
   This stuff is all pretty simple. The mortise depth has to be sufficient to house the tenon. Maybe I should talk like my second son and say, "the mortise should barely hold the tenon." You see, Patrick is a civil engineer with a specialty in bridges. He says that anyone can design a bridge which stands. But it takes a civil engineer to design a bridge which barely stands. Maybe we should speak of love affairs between mortises and tenons, and that the mortise should wrap itself tightly but lovingly around the tenon - not so much so as to smother the relationship, but sufficient that it sustain the relationship over time.I believe we now have that one solved.
   MelPS on Tues night, I went to the woodworking guild meeting. After the meeting I saw the guy who keeps the videos. He had asked for suggestions for the purchase of new videos. I asked about getting a few by Nora Hall on woodcarving. His response was that woodcarving is not a real part of woodworking and so it would not be appropriate to have videos in that area. I felt like I had entered the twilight zone. I thanked him for his time and left. It was sort of like going to a history club meeting and having the librarian tell you that Eric the Red was Constantine's son-in-law, and and that he discovered the Milky Way. Life on the outskirts of woodworking is a wonderful place.Measure your output in smiles per board foot. 

1. 
   pzgren | May 17, 2007 10:07pm | #8

   Mel,

     <<Maybe I should talk like my second son and say, "the mortise should barely hold the tenon." You see, Patrick is a civil engineer with a specialty in bridges. He says that anyone can design a bridge which stands. But it takes a civil engineer to design a bridge which barely stands.>>

     Old engineering joke:

   "What's the difference between a mechanical engineer and a civil engineer?"

   "A mechanical engineer builds weapons. A civil engineer builds targets."

     Another old engineering joke:

   An optimist say that the glass is half full.

   A pessimist says that the glass is half empty.

   An engineer says that the glass is too big to begin with.

   Cheers!

   .<!----><!----><!---->

   Tschüß!<!----><!---->

   <!----><!---->James<!----><!---->

   <!----> <!---->

   "I'm sorry, Dave, I'm afraid I can't do that...."

    

   -- A.C. Clarke

2. 
   joinerswork | May 18, 2007 12:50am | #9

   Ah, Mel,

   You are correct, that a mortise need only be deep enough to contain its tenon. I'll try and read the question more carefully in future.  But your post reminded me of a question once posed to Abe Lincoln, as a way of commenting on his tallness: "Mr Lincoln, how long do you suppose a man's legs ought to be?"  His reply, "Just long enough to reach from his hips, to the ground."  All this kidding around about tenons and such might be summed up by the old woodworking expression, "The mortiser, the merrier."

   One of my close friends is an engineer.  I'm continually non-plussed by the way his mind works.  Totally different head, as a tv character used to say.

   Cheers,

   Ray

   p.s. Perhaps your guild member's feelings about carving and its (non) place in the realm of woodworking came about as a result of the talk and demo I gave there on shell carving,  a couple years ago...perfectly understandable reaction!

4. 
   Routerman | May 17, 2007 04:12pm | #4

   Typical depth of mortice = 2/3 of thickness. Tho pull strength is of main concern, it can be substantial when the tenon is short & pinned, the mortice shallow, or with the addition of hardware. Moreover, assembly, x itself, can lock a stick in place, and then pull strength is not much of an issue.

   Mortice straight bit in link designed specifically for cuts >2" deep.

5. 
   AdamCherubini | May 17, 2007 07:18pm | #5

   I know of no rule of thumb.  If you are pegging the tenon, I would make the tenon at least 4X the diameter of the peg.  So a 1/4" peg would need a 1" deep tenon at least.

   If you're not going to peg it or its a chair or something that will see a rotation in use, I would make the mortise as deep as possible.  The stress inside the mortise will be lessened.

   Lastly, I recommend caution with glued mortises.  PVA is probably not your best bet (since it requires bondline pressure to develop properties).  A slightly rough or gappy mortise (on the tenon cheeks) and epoxy or hide glue would be stronger.  If longevity is a concern, choose hot hide glue. 

   That apron sounds really deep. You might want to split the tenon into an upper and lower.  I think this was done to save time mortising, but I can think of a few minor structural advantages.

   Adam

6. 
   CharlieStanford | May 17, 2007 09:18pm | #6

   1) Two thirds the width of the piece to be mortised....

   2) Five times the thickness of the tenon....

   Two general rules of thumb.  Take them for what they're worth.