If glue is stronger than the wood, do you need to use screws when attaching legs to a table?

YJJim wrote:

> The comment about glue being stronger than the wood makes me wonder if
> I could just face glue the legs to the inside of the frame. (hope my
> description has made this make sense). Would this be strong enough?
> Or do I need screws or a bolt? Would the torsional forces of kids
> pushing the table around or leaning on it break the glue joint? If
> the glue is "truly" stronger than the wood, I would think that the
> legs would break before the joint. If this is the case, the bolts
> don't add any strength.

If I understand the construction method correctly what you've described is
a cross grain situation. Because of wood movement glue joints are prone
to fail in this arrangement. I would use the mechanical fasteners.

--
Jack Novak
Buffalo, NY - USA
(Remove "SPAM" from email address to reply)

It is true that a good glue joint is stronger then the wood itself but too
many people take that at face value. That statement is only half the story,
the other half is glue area. Put two pieces of wood togeather with just a
dab of glue in the middle and that joint will fail, at the glue joint, under
much less pressure then it would had the whole width been glued.

On an ordinary table, say a dining room table, constructed with a skirt
mortised and tenoned into the legs you will usually find some form of
mechanical cross anchors at the corners. They aren't there because the glue
joint is particularly weak but rather due to the fact there is a relatively
small area glued up and there is a need to spread the various stresses of
lateral forces that will be applied to the table during it's life IE sliding
it across a floor when it is moved or someone has to push it away after
particularly good thanksgiving turkey dinner.

From your description of the construction I think there will be enough
exposed area in enough directions that any mechanical fastening wouldn't be
necessary and there isn't enough cross grained glued up wood to where you
will have problems with wood movement. Plus, yellow glue does say somewhat
flexible and will accommodate the small amount of movement you would
experience. For those that have a problem with that statement please look up
"glue creep"

However, if you don't feel confident in doing the job without some
additional bracing I'd suggest some 1/4" dowels glued through the joint.
They will do the same job as screws or bolts and can look quite decorative
at the same time.

My preference for glue is either hide glue or yellow glue. For various
reasons I don't like poly glue and only use it for special glue up problems
but, to give the devil it's due, it will do the job of securely joining two
pieces of wood. If you want to give it a try, have at it. You won't be
gaining or losing anything in terms of strength.

Good luck
--
Mike G.
[email protected]
Heirloom Woods
www.heirloom-woods.net
"YJJim" <[email protected]> wrote in message
news:[email protected]...
> I am finishing up a train table (for Thomas/Brio train stuff) for my
> son and I have been planning to attach the legs to the table using
> screws or bolts. I have heard many people say that a glue joint is
> stronger than the wood itself. If this is true, do you really need a
> mechanical fastener?
>
> Basic description of my design: I have a 1x4 frame for the the table.
> I have a dado running a ring around the frame about 1" above the
> bottom with a 1x2 in the dado to support the table (this gives about a
> 1" lip around the top to keep the trains from rolling off). The legs
> are two 1x3s glued to form an 'L' and are about 18" long. The legs
> fit inside the frame (or skirt, I guess you could call it), and extend
> about 1" inside. Thus, there is about a 1"x3" rectangle of surface
> area where the legs contact the table frame. I have been planning to
> run bolts (something nice looking) through the table frame and legs to
> securely fasten the legs to the table.
>
> The comment about glue being stronger than the wood makes me wonder if
> I could just face glue the legs to the inside of the frame. (hope my
> description has made this make sense). Would this be strong enough?
> Or do I need screws or a bolt? Would the torsional forces of kids
> pushing the table around or leaning on it break the glue joint? If
> the glue is "truly" stronger than the wood, I would think that the
> legs would break before the joint. If this is the case, the bolts
> don't add any strength.
>
> If I just use glue, should I use gorilla glue? Or is plain yellow
> glue strong enough? (I recently bought some gorilla glue, but have
> never used it)
>
> Thanks,
> YJJim

Most glues are stronger than the wood, but if you are going to change
directions of the grain when gluing, such as long grain to side grain, the
natural expansion and contraction of the wood will eventually break the
bond. Also consider that table legs can be subject to loads that quite
possibly could be greater than the woods natural strength. The wood may
break itself. Using screws can add strength as the screw uses the strength
of the thickness of the board vs. the surface of the board strength.

Use screws or bolts (and maybe washers) to spread the forces
throughout the thickness of the leg and skirt. Otherwise, the glue
will hold well enough to pull the wood fibers off the surface of the
leg or skirt.



[email protected] (YJJim) wrote:

>The comment about glue being stronger than the wood makes me wonder if
>I could just face glue the legs to the inside of the frame. (hope my
>description has made this make sense). Would this be strong enough?
>Or do I need screws or a bolt? Would the torsional forces of kids
>pushing the table around or leaning on it break the glue joint? If
>the glue is "truly" stronger than the wood, I would think that the
>legs would break before the joint. If this is the case, the bolts
>don't add any strength.
>
>If I just use glue, should I use gorilla glue? Or is plain yellow
>glue strong enough? (I recently bought some gorilla glue, but have
>never used it)
>
>Thanks,
>YJJim