Are there guidlines on what size of mortis and tennon joint to make for
a particular wood thickness?
I just had a project go really bad.
Wanting to learn how to make mortis and tenon joints I decided to make a
simple chair. I have made some test joints that seemed to fit and work
First I purchased some 1x2 pine at home depot thinking it was not too
expensive and if it did not work I would not be burning too much wood
(using pine of such small dimension was probably my first mistake).
All the joints fitted nicely but while trying to assemble the last
couple pieces I was having trouble getting the last couple tenons
together after applying glue and using a hammer to force the issue when
first one piece of wood split and then another and the chair is no
more. Being new to this, are there guidlines on what size of mortis and
tennon joint to make for a particular wood thickness?
One suspicion that I have is that 1 inch pine with a mortis cut into it
is too weak. Once christmas is over I'm going to try some 1x2 maple and
see how it works. Or should I try for something thicker for starters
We are planning on having a fire in the fireplace on christmas and I
have lots of fresh kindling to start it.
Biggest mistake we make is trying to make the joint too tight. In reality,
the joint bears on end grain surfaces at shoulders and the gravity side of
the mortise. The cheeks need not be tight, because they're really not the
bearing portion of the joint.
If you can't dry fir the joint with ease, you should get out your plane and
chisel and trim the cheeks. If you insist on putting a lot of glue in, make
sure you don't bottom the tenon, and run a relief channel for air to fart
out as you assemble. On pine, enough to run a screwdriver and press, some
run a veiner or macaroni gouge groove in hardwood.
One third to one half the thickness is standard tenon. Wider the tenoned
piece (more end grain bearing), the thinner the tenon may be.
RULE: Tenon is 1/3 to 1/2 the thickness of the wood it enters.
1 of 837 from Amazon.com:
Making Mortise and Tenon Joints
by Taunton Press
From our local library:
search for "joinery"
Woodworking techniques : joints and their applications
Author: DeCristoforo, R. J.
Notches of all kinds : a book of timber joinery
Author: Mackie, B. Allan.
Author: Hayward, Charles Harold
Practical & decorative woodworking joints
Author: Bairstow, John E. N.
Joining wood : techniques for better woodworking
Author: Engler, Nick.
The encyclopedia of jointmaking
Author: Noll, Terrie.
search for "chairs"
Make a chair from a tree : an introduction to working green wood
Author: Alexander, John D.
The chairmaker's workshop : handcrafting Windsor and post-and-rung
Author: Langsner, Drew.
Making classic chairs : a craftsman's Chippendale reference Book
Author: Clarkson, Ron.
The weekend woodworker : 40 easy-to-build projects : shelves and
cabinets, toys, tables and chairs, boxes and mirrors
Publisher: Rodale Press
Fat girls and lawn chairs
Author: Peck, Cheryl. (No idea what you'll find there)
Make a Windsor chair with Michael Dunbar
Author: Dunbar, Michael.
Fine woodworking on chairs and beds : 33 articles
Publisher: Taunton Press
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I had done a test fit of the entire chair before I begain gluing.
Everything fit and not so snug that
I had to pound it together.
I'm now thinking the most likely cause is too much glue in the holes.
Some bleed holes out
the other end might be the solution. I have the home depot maple and as
soon as weather
permits I'm going to make another stab at it. However, I'm debaiting
picking up some wider
maple at paxtons for the back legs and the back cross piece that failed
on the pine.
One problem early on is that I realized too late that I was gluing the
chair pieces in the wrong
order making it difficult to make the final assembly.
Mark & Juanita wrote:
I do WW for a living (hey, call that a living....) but I periodically
make-up one-off mortised and tenoned doors. The normal practice with these
is to leave a "horn" on the end of the stile pieces (generally some 2 to 3in
long) which you have mortised. The door is thus delivered to site with the
horns intact and these are sawn off by the installation carpenter before he
hangs the door in the frame. Ths is traditional English practice and is done
for two reasons - first pine can be pretty variable stuff and it is easy to
"pop" out the thin piece of wood at the end of a stile, especially if you
are foxing (i.e. wedging) the joint - secondly the horns protect the top and
bottom of the door during transit. There is less of a need to do this with
hardwoods, but I still habitually leave about a 3/4 to 1in horn on these,
too. Even so, fit is important - your tenons should slide into the mortises
with a little bit of resistance - remember, you'll need somewhere for the
glue to go and if your M&T is very tight and you are using a water based
glue (PVA, aliphatic resin, etc) a very tight joint can "burst" through
fibre expansion, especially if you haven't got horns at the end.
Hope this helps
A couple of things. The first is, as a general rule-of-thumb is to divide
your thickness into 1/3rds for the strongest joint. However, it makes
things much simpler, whatever method you are using, to make your mortice the
same width as your tool, be it hand chisel, morticing machine, or router
bit. So select your tool to be as near to 1/3 the width as you can for
maximum strength and maximum convenience.
The second is that pine is pretty variable. If you get old-growth stuff
which was slow-grown in a high latitude, the rings will be tightly-packed
and the timber quite dense, and it'll make a strong constructional timber.
If you buy cheap stuff from a builders yard, which is more appropriate for
making a stud wall, then you may find that it's fast-grown and harvested
young, so the growth rings are widely spaced, and it's not really fit for
something to take the huge stresses that a chair will have to take. If
you've got a slim chair with a 200lb man rocking back in it, the joints are
under huge pressure. 1" stuff might be ok in top-quality clears, but if
you're using 5ths or 6ths stuff, then you might want to go up to 1 3/8" or
The third thing to consider is that if the mortice is at the end of the
component, then there's not too much wood between the end of the mortice and
the end of the component, perhaps as little as 1/4". so when you come to
drive home a fairly tight-fitting tenon (as I personally believe they should
be) then it's going to split out. The solution here is to mark up the
component with the mortice to size, but *don't* cut it to size - if
possible - until after glue-up: leave a few inches of overhang on the end
nearest the mortice (we call these overhangs "horns"). This will greatly
reinforce the joint when you're malleting the tenon home.
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