"dpb" <[email protected]> wrote in message news:[email protected]...
> Larry Blanchard wrote:
> ...
>> If the aprons were glued only at the top, there wouldn't be sufficient
>> support for the legs. What I would do is separate the single large tenon
>> into three smaller ones (2"-3"-2") with space between them and at the
>> ends
>> of the mortise. Then I'd glue only the top and bottom 2" tenons and let
>> the middle 3" one float.
> ...
> Not seen what they're actually doing, either, but seems like that would
> still be an issue as the middle one isn't the one that needs to move.
> Seems like two fixed tenons on either side of a 8" wide piece even
> individually narrow are still likely to need some way to move relative to
> each other or will eventually fail the joint.
I don't recall a mention of the parts thickness, but a time honored general
'rule of thumb' is that a tenon should be no wider than 5 times it's
thickness before going to another tenon.
This is pretty standard stuff in door making, which makes liberal use of
double tenons on some pretty wide rails, with either a space or haunch in
the middle, each component being no more than 1/3rd the width of the rail.
Depending upon thickness, on a wide table apron I'd probably forego a haunch
in the middle, but use a "haunched mortise and tenon" for the top tenon of
double tenons, so it doesn't break through the leg endgrain.
Following either above, it is accepted practice to glue both the top and
bottom tenons. I've never had trouble doing that, but nothing I've built has
been around longer than 45 years either.
--
www.e-woodshop.net
Last update: 8/18/08
KarlC@ (the obvious)
Larry Blanchard wrote:
> In the current issue of WOOD magazine, they give plans for a nightstand.
> The side and back aprons are 8.75" deep with 8.25" tenons. The tenons are
> cross-grain glued into the legs!
>
> Has someone repealed the laws of wood movement?
If it's in a conditioned/humidified house it may not be too bad.
However, build it in arizona and take it to florida and you'd probably
be asking for trouble.
Chris
On Fri, 03 Oct 2008 19:48:45 -0700, Larry Blanchard
<[email protected]> wrote:
>In the current issue of WOOD magazine, they give plans for a nightstand.
>The side and back aprons are 8.75" deep with 8.25" tenons. The tenons are
>cross-grain glued into the legs!
>
>Has someone repealed the laws of wood movement?
>
>I think I'll write them and ask :-).
I had not seen this yet (are you referring to Nov or Dec 08?), but if
there are 8.25" tenons just apply glue to the top 3-4 " of the tenon
to allow for movement.
Larry Blanchard wrote:
...
> If the aprons were glued only at the top, there wouldn't be sufficient
> support for the legs. What I would do is separate the single large tenon
> into three smaller ones (2"-3"-2") with space between them and at the ends
> of the mortise. Then I'd glue only the top and bottom 2" tenons and let
> the middle 3" one float.
...
Not seen what they're actually doing, either, but seems like that would
still be an issue as the middle one isn't the one that needs to move.
Seems like two fixed tenons on either side of a 8" wide piece even
individually narrow are still likely to need some way to move relative
to each other or will eventually fail the joint.
--
On Sat, 04 Oct 2008 09:11:27 -0400, Phisherman wrote:
>
> I had not seen this yet (are you referring to Nov or Dec 08?), but if
> there are 8.25" tenons just apply glue to the top 3-4 " of the tenon
> to allow for movement.
I know that, but apparently they don't. In addition they left no slop in
the mortise to allow for such expansion.
If the aprons were glued only at the top, there wouldn't be sufficient
support for the legs. What I would do is separate the single large tenon
into three smaller ones (2"-3"-2") with space between them and at the ends
of the mortise. Then I'd glue only the top and bottom 2" tenons and let
the middle 3" one float.
I'm referring to the Nov/Dec issue as it's only published every other
month.