I have a question for those of you with more experience than me (which
is probably most of you). While watching NYW, the first part of the
Routers 101 episodes, Norm was extolling the vrtues of routers using a
small part of his infintesimal collection and he plowed a mortise using
a plunge router, a fence and a spiral bit. Nothing earthshaking, but
when he got through he tested the fit with a piece that he had made a
tenon on and he said that it fit great and that (this is the part that
threw me) there was some play along the long axis, (looked like about
3/16" to me), but that he wanted that so that he had some "room for
adjustment during final glue up". ????????? Now I'll admit that my
training on mortise and tenon joinery was far from extensive, but I
don't ever remember seeing anyone recomend leaving "play" along the
long axis. I was always taught that you made the tenon fit snuggly on
all four sides leaving just enough room for glue and to make the
mortise deep enough that the tenon didn't bottom out. Wouldn't "play"
eliminate some of the joint's strength along the long axis? Is this
just a Normism like his favorite "few brads to hold it while the glue
dries" or is this a common practice and my mortise and tenon training
wasn't just far from extensive but down right deficient? Thanks in
advance for your input. bc
"Swingman" <[email protected]> wrote in message
news:[email protected]...
> "robo hippy" wrote in message
>> Maybe I am missing something here, but I always leave a little wiggle
>> room in the mortice.
>
> Six of one, half dozen of the other ... A little "wiggle room", upon which
> the OP was remarking/accusing Norm of sloppiness, means the tenon is too
> short, in height, for the mortise, or the mortise is too tall for the
> tenon.
>
> ... or maybe it's me who's missing something?
Then we both are missing something.
Chuck Taylor wrote:
> On 2 Mar 2006 14:51:04 -0800, "bc" <[email protected]> wrote:
>
> >I was always taught that you made the tenon fit snuggly on
> >all four sides leaving just enough room for glue and to make the
> >mortise deep enough that the tenon didn't bottom out. Wouldn't "play"
> >eliminate some of the joint's strength along the long axis? Is this
> >just a Normism like his favorite "few brads to hold it while the glue
> >dries" or is this a common practice and my mortise and tenon training
> >wasn't just far from extensive but down right deficient?
>
>
> You're right. Mortise and tenon joints are supposed to be snug all
> around, otherwise they're *weak*. Norm had an opportunity to teach
> novices a lesson by saying, "Oops, I made a mistake", but he didn't.
A little wiggle room is acceptable for adjustment and sanity. Two
faces of the tenon are glued to end grain, so there's no strength to
speak of there. The only way that the tenon's narrow sides would come
into play is if the face-to-face glue joint failed.
I personally don't see a problem with doing it either way, assuming the
tenon height isn't ridiculously long where cross grain movement would
be an issue, but I don't think the little bit of wiggle room would
affect the joint strength appreciably.
That being said, a joint subject to heavy stress and impacts should
probably fit tighter than the run of the mill joint. It would be an
interesting thing to test.
As a related question, does anyone have knowledge of the relative
strengths of dry-pegged mortise and tenon vs. glued? I've seen tests
on various glued joints, but never wet vs. dry.
R
Leuf wrote:
> On Fri, 03 Mar 2006 01:34:41 GMT, "Leon"
> <[email protected]> wrote:
>
> >Well really the mortise and tennon gets strength by the rather large surface
> >area that is glued on the wide flat sides of the tennon that is inside the
> >joint. That is where the proper fit is important concerning the glued
> >surface. The small amount at the top and bottom adds negelable strength by
> >comparison.
>
> The surface area it provides may be small compared to the faces (maybe
> not depending on the joint) but imagine a torque being applied to the
> joint. The ends fitting tightly provides a mechanical stop to this
> type of force, even without glue it won't come apart. It doesn't do a
> whole lot to prevent the joint from being pulled straight apart
> though. So depending on the application it can make a difference.
If the glued joint were flexible, I suppose that the torque could put
pressure on the top and bottom of a tight mortise. But the glue joint
is not flexible. How can the torque exert a force without failure of
the main gluing surfaces?
R
RicodJour wrote:
> Leuf wrote:
> > On Fri, 03 Mar 2006 01:34:41 GMT, "Leon"
> > <[email protected]> wrote:
> >
> > >Well really the mortise and tennon gets strength by the rather large surface
> > >area that is glued on the wide flat sides of the tennon that is inside the
> > >joint. That is where the proper fit is important concerning the glued
> > >surface. The small amount at the top and bottom adds negelable strength by
> > >comparison.
> >
> > The surface area it provides may be small compared to the faces (maybe
> > not depending on the joint) but imagine a torque being applied to the
> > joint. The ends fitting tightly provides a mechanical stop to this
> > type of force, even without glue it won't come apart. It doesn't do a
> > whole lot to prevent the joint from being pulled straight apart
> > though. So depending on the application it can make a difference.
>
> If the glued joint were flexible, I suppose that the torque could put
> pressure on the top and bottom of a tight mortise. But the glue joint
> is not flexible. How can the torque exert a force without failure of
> the main gluing surfaces?
>
Precisely.
Glues are strongest in shear.
--
FF
Maybe I am missing something here, but I always leave a little wiggle
room in the mortice. The tenon is cross grain, and the mortice is long
grain. The tenon will move more that the mortice, and the glue joint,
at least part of it will fail eventually because there is a big
difference in how much movement there is in each piece. This is why you
should use dowels, and some people will only glue only the top part of
the tenon and use a slot cut in the tenon for the bottom dowel. If the
tenon is small, say 2 inches of so, it won't make a whole lot of
difference, but if it is longer, say 5 or so inches, then it can make a
difference. If you are making a big joint say 12 inches it would be
suicide to glue the whole thing.
robo hippy
Having a little "adjustment room" probably isn't all
that handy in say a bottom stretcher of a trestle
table. But it sure comes in handy with the apron
to leg joint of a table. You don't have to be off much
in either the mortise or tenon or both to end up with
the top of the apron a little above the top of the leg
(something a block plane could probably "fix" or
worst case - apron BELOW the to of the leg. The
latter is not easily corrected The joint might
fit nice and tight - but the alignment of the parts
will be a problem.
As noted, it's the sides and glue that provide
the resists up/down movement and in/out
movement. The cheeks control rotation
Maybe this will help
http://home.comcast.net/~charliebcz/MtPrimer4.html
Having a little wiggle room BEFORE the glue
starts to set is handy.
charlie b
"Leon" <[email protected]> wrote in message
news:[email protected]...
>
> "Swingman" <[email protected]> wrote in message
> news:[email protected]...
>> "robo hippy" wrote in message
>>> Maybe I am missing something here, but I always leave a little wiggle
>>> room in the mortice.
>>
>> Six of one, half dozen of the other ... A little "wiggle room", upon
>> which
>> the OP was remarking/accusing Norm of sloppiness, means the tenon is too
>> short, in height, for the mortise, or the mortise is too tall for the
>> tenon.
>>
>> ... or maybe it's me who's missing something?
>
>
> Then we both are missing something.
>
The mortise should always be a bit deeper than the tenon length to allow a
place for air and glue. Else, it will require some retightening of clamps
as they are slowly expelled, or rapidly, with some interesting sounds.
Since wood expands when wet glue is applied, the cheeks should be a touch
loose. The glue will keep the wood expanded or fill the gap.
Reason for the glue is to keep the tenon from withdrawing. The strength of
the joint against deforming is in the shoulders. As you know, standard post
and beam construction uses no glue, but draw bores dry tenons for pins to
keep the tenon from withdrawing and the shoulders in register. The static
load is borne on the long grain post, not the beam or stringer, where it
might creep or deflect over length.
"Leon" <[email protected]> wrote in message
news:[email protected]...
>
> "Swingman" <[email protected]> wrote in message
> news:[email protected]...
>>
>> The "depth" of mortise not under discussion in this thread ... the
>> length,
>> yes.
>>
>
> Times like this a picture would be worth a thousand words.
>
Or, you could read the thread rather than quote the preamble.
The m/t joint is designed to create and maintain a right angle relationship.
The load is presumed to be on the virtually incompressible end grain of the
mortised piece, with the tenoned piece merely making dimension and square.
If you were planning a significant load on the piece with the tenons - a bad
move - you would be well-advised go to a bridle joint, which is designed to
bear such a load, and brace in the middle to limit deformation.
To sum up - if the joint is being used properly, doesn't make a rats ass if
the bottom of the tenon rests on the wood at the bottom of the mortise. It
should not be loaded in that direction anyway.
"bc" <[email protected]> wrote in message
news:[email protected]...
>I have a question for those of you with more experience than me (which
> is probably most of you). While watching NYW, the first part of the
> Routers 101 episodes, Norm was extolling the vrtues of routers using a
> small part of his infintesimal collection and he plowed a mortise using
> a plunge router, a fence and a spiral bit. Nothing earthshaking, but
> when he got through he tested the fit with a piece that he had made a
> tenon on and he said that it fit great and that (this is the part that
> threw me) there was some play along the long axis, (looked like about
> 3/16" to me), but that he wanted that so that he had some "room for
> adjustment during final glue up". ????????? Now I'll admit that my
> training on mortise and tenon joinery was far from extensive, but I
> don't ever remember seeing anyone recomend leaving "play" along the
> long axis. I was always taught that you made the tenon fit snuggly on
> all four sides leaving just enough room for glue and to make the
> mortise deep enough that the tenon didn't bottom out. Wouldn't "play"
> eliminate some of the joint's strength along the long axis? Is this
> just a Normism like his favorite "few brads to hold it while the glue
> dries" or is this a common practice and my mortise and tenon training
> wasn't just far from extensive but down right deficient? Thanks in
> advance for your input. bc
>
I never leave anywhere near 3/16th inch but always leave a little bit of
adjustment room in the long axis and depth. I believe that the strength
from the cheeks and shoulders is the most important.
"robo hippy" wrote in message
> Maybe I am missing something here, but I always leave a little wiggle
> room in the mortice.
Six of one, half dozen of the other ... A little "wiggle room", upon which
the OP was remarking/accusing Norm of sloppiness, means the tenon is too
short, in height, for the mortise, or the mortise is too tall for the tenon.
... or maybe it's me who's missing something?
--
www.e-woodshop.net
Last update: 12/13/05
"Chuck Taylor" <[email protected]> wrote in message
news:[email protected]...
> On 2 Mar 2006 14:51:04 -0800, "bc" <[email protected]> wrote:
>
>>I was always taught that you made the tenon fit snuggly on
>>all four sides leaving just enough room for glue and to make the
>>mortise deep enough that the tenon didn't bottom out. Wouldn't "play"
>>eliminate some of the joint's strength along the long axis? Is this
>>just a Normism like his favorite "few brads to hold it while the glue
>>dries" or is this a common practice and my mortise and tenon training
>>wasn't just far from extensive but down right deficient?
>
>
> You're right. Mortise and tenon joints are supposed to be snug all
> around, otherwise they're *weak*. Norm had an opportunity to teach
> novices a lesson by saying, "Oops, I made a mistake", but he didn't.
Well really the mortise and tennon gets strength by the rather large surface
area that is glued on the wide flat sides of the tennon that is inside the
joint. That is where the proper fit is important concerning the glued
surface. The small amount at the top and bottom adds negelable strength by
comparison. With that in mind if you have some play at each end it makes it
much easier to dry test fit and take apart and most often the up or down fit
at the top or bottom of the joint is more important in relation to other
pieces of wood.
"George" wrote in message
> "Leon" wrote in message
>
> >
> > "Swingman" wrote in message
> >
> >> "robo hippy" wrote in message
> >>> Maybe I am missing something here, but I always leave a little wiggle
> >>> room in the mortice.
> >>
> >> Six of one, half dozen of the other ... A little "wiggle room", upon
> >> which
> >> the OP was remarking/accusing Norm of sloppiness, means the tenon is
too
> >> short, in height, for the mortise, or the mortise is too tall for the
> >> tenon.
> >>
> >> ... or maybe it's me who's missing something?
> >
> >
> > Then we both are missing something.
> >
>
> The mortise should always be a bit deeper than the tenon length to allow a
> place for air and glue.
The "depth" of mortise not under discussion in this thread ... the length,
yes.
--
www.e-woodshop.net
Last update: 12/13/05
"bc" wrote in message
> eliminate some of the joint's strength along the long axis? Is this
> just a Normism like his favorite "few brads to hold it while the glue
> dries" or is this a common practice and my mortise and tenon training
> wasn't just far from extensive but down right deficient? Thanks in
> advance for your input. bc
I doubt that it was 3/16, but even then with a stopped M & T joint a little
"adjustment room" is nothing to worry about as long as the shoulders fit
snug.
--
www.e-woodshop.net
Last update: 12/13/05
"Leuf" <[email protected]> wrote in message
news:[email protected]...
> On Fri, 03 Mar 2006 01:34:41 GMT, "Leon"
> <[email protected]> wrote:
>
>>Well really the mortise and tennon gets strength by the rather large
>>surface
>>area that is glued on the wide flat sides of the tennon that is inside
>>the
>>joint. That is where the proper fit is important concerning the glued
>>surface. The small amount at the top and bottom adds negelable strength
>>by
>>comparison.
>
> The surface area it provides may be small compared to the faces (maybe
> not depending on the joint) but imagine a torque being applied to the
> joint.
I can see your point here.
The ends fitting tightly provides a mechanical stop to this
> type of force, even without glue it won't come apart.
I still believe that the glue will be strong enough only on the wide side of
the tennon. The joint that the OP was talking about IMHO would not have
benefitted from a tighter fit on the narrow sides.
On Fri, 03 Mar 2006 01:34:41 GMT, "Leon"
<[email protected]> wrote:
>Well really the mortise and tennon gets strength by the rather large surface
>area that is glued on the wide flat sides of the tennon that is inside the
>joint. That is where the proper fit is important concerning the glued
>surface. The small amount at the top and bottom adds negelable strength by
>comparison.
The surface area it provides may be small compared to the faces (maybe
not depending on the joint) but imagine a torque being applied to the
joint. The ends fitting tightly provides a mechanical stop to this
type of force, even without glue it won't come apart. It doesn't do a
whole lot to prevent the joint from being pulled straight apart
though. So depending on the application it can make a difference.
-Leuf
On 2 Mar 2006 14:51:04 -0800, "bc" <[email protected]> wrote:
>I was always taught that you made the tenon fit snuggly on
>all four sides leaving just enough room for glue and to make the
>mortise deep enough that the tenon didn't bottom out. Wouldn't "play"
>eliminate some of the joint's strength along the long axis? Is this
>just a Normism like his favorite "few brads to hold it while the glue
>dries" or is this a common practice and my mortise and tenon training
>wasn't just far from extensive but down right deficient?
You're right. Mortise and tenon joints are supposed to be snug all
around, otherwise they're *weak*. Norm had an opportunity to teach
novices a lesson by saying, "Oops, I made a mistake", but he didn't.
--
Chuck Taylor
http://home.hiwaay.net/~taylorc/contact/
On 2 Mar 2006 15:52:17 -0800, "RicodJour" <[email protected]>
wrote:
>Chuck Taylor wrote:
>> On 2 Mar 2006 14:51:04 -0800, "bc" <[email protected]> wrote:
>>
>> >I was always taught that you made the tenon fit snuggly on
>> >all four sides leaving just enough room for glue and to make the
>> >mortise deep enough that the tenon didn't bottom out. Wouldn't "play"
>> >eliminate some of the joint's strength along the long axis? Is this
>> >just a Normism like his favorite "few brads to hold it while the glue
>> >dries" or is this a common practice and my mortise and tenon training
>> >wasn't just far from extensive but down right deficient?
>>
>>
>> You're right. Mortise and tenon joints are supposed to be snug all
>> around, otherwise they're *weak*. Norm had an opportunity to teach
>> novices a lesson by saying, "Oops, I made a mistake", but he didn't.
>
>A little wiggle room is acceptable for adjustment and sanity. Two
>faces of the tenon are glued to end grain, so there's no strength to
>speak of there. The only way that the tenon's narrow sides would come
>into play is if the face-to-face glue joint failed.
I'll certainly accept that there's room for more than one opinion, but
I've always figured that was the purpose of a good chisel and/or
shoulder plane--even on the narrow sides of the joint.
--
Chuck Taylor
http://home.hiwaay.net/~taylorc/contact/
"RicodJour" <[email protected]> wrote in message
news:[email protected]...
>
> If the glued joint were flexible, I suppose that the torque could put
> pressure on the top and bottom of a tight mortise. But the glue joint
> is not flexible. How can the torque exert a force without failure of
> the main gluing surfaces?
The biscuit joint uses the same principal. The thickness is important but
the side to side play is not that important.
On Sat, 4 Mar 2006 07:01:23 -0500, "George" <George@least> wrote:
>To sum up - if the joint is being used properly, doesn't make a rats ass if
>the bottom of the tenon rests on the wood at the bottom of the mortise. It
>should not be loaded in that direction anyway.
I think I appreciate the replies at least as much as the OP. Time to
give my own opinion a little "wiggle room".
--
Chuck Taylor
http://home.hiwaay.net/~taylorc/contact/
On 2 Mar 2006 20:20:10 -0800, "RicodJour" <[email protected]>
wrote:
>Leuf wrote:
>> The surface area it provides may be small compared to the faces (maybe
>> not depending on the joint) but imagine a torque being applied to the
>> joint. The ends fitting tightly provides a mechanical stop to this
>> type of force, even without glue it won't come apart. It doesn't do a
>> whole lot to prevent the joint from being pulled straight apart
>> though. So depending on the application it can make a difference.
>
>If the glued joint were flexible, I suppose that the torque could put
>pressure on the top and bottom of a tight mortise. But the glue joint
>is not flexible. How can the torque exert a force without failure of
>the main gluing surfaces?
Good point. It probably doesn't even make any difference in most
situations.
However, as far as having wiggle room at assembly time goes. If
you've got room to move it around to where you want it then there's
also room for things to move out of place while you are getting clamps
on. I'd rather start with it too tight and get it so it can only fit
correctly aligned during dry fit. Otherwise it will never go back
together exactly the same once you've got glue on the sucker.
I did see Norm doing what the OP referred to, and if I remember
correctly he didn't square off the mortice or round the tenon, so it
probably looked like there was more room for it to move than there
was. I can understand that since the episode was about how to use a
router not how to make a M&T that he might skip rounding the corners
just to get on with it. Every other time I've seen him do it he
either squared the mortice or rounded the tenon, and I've never seen
him say anything about leaving space before either.
-Leuf
"Swingman" <[email protected]> wrote in message
news:[email protected]...
>
> The "depth" of mortise not under discussion in this thread ... the length,
> yes.
>
Times like this a picture would be worth a thousand words.
> --
> www.e-woodshop.net
> Last update: 12/13/05
>
>