Subject: Glue vs screwing large top on Cabinet ?

From: [email-masked] (Peter Neil)
Date: 1 Apr 1997 17:19:36 GMT

Hi,

I'm a relative newbie starting my first major (for me anyway)
project.  I'm going to build the following out of 3/4" Red Oak.

Free standing cabinet:

	o solid wood slab construction (glued panels)
	o case approx 48" wide and 16" deep
	o top approx 1" wider and deeper
	o two doors
	o solid divider (will also serve as the inside 'stop/rest'
	  for the doors).

I'm planning on rabbeting the base, back, and sides and then glueing these
four pieces solid.  The divider will sit in a dado on the base but not be
glued to the back.

Originally I was planning to cut dado's/grooves into the top and then glueing
the sides and back directly into these cuts. The grain on the top and back will
be horizontal and vertical on the sides.  To my untrained (uneducated ?) eye
these joints would be really solid and basically last forever.

HOWEVER, I've been told that I should NOT glue but use something like screw 
blocks in the four inside corners that would be both screwed to the
sides/back and to the top.  The reason I was given is that the sides will
expand outward when the humidity increases here (Massachusetts) in the
summer and basically tear the top apart...

With screws I'll be worried that they won't stand up over time since this is
going to be one heavy beast after it's done.

Also, for what it's worth, I was planning on 3 or so coats of a polyurethane
finish for durability.

Comment and suggestions will be most welcome.

Thanks,

Peter Neil.

---

From: [email-masked] (Douglas Bailey)
Date: 1 Apr 1997 21:09:35 GMT

If I'm clear on what you're describing here, you can do better.

If you are using all solid wood, as you seem to be, you need to make
sure that you don't have any cross-grain joints.  This is fairly easy
on a cabinet as you describe: grain on the sides goes up/down,
grain on top and bottom go left/right.  Need to fuss a bit with the
back (more on this later).

The reason for this is that wood expands and contracts with the
changing seasons, and doesn't do it evenly.  It doesn't change much at
all with the grain, but changes quite signficantly across the grain.

So, for example, if you were to join two pieces of wood like:

         ----
         |  |_______
         |  |      |
         |  |______|
         |  |
         ----

where the grain runs the lengths of the boards, you would run into
problems.  Along the glue line, the left board would be relatively
stable (it would expand and contract perpendicular to the glue line,
but the glue line itself would remain stable), but the right board
would move (the right board will grow wider with increased humidity,
narrower with decreased humidity).  This will eventually break the
glue bond.

So, make sure that when you build this thing, you don't introduce any
cross grain joints.  Easy to do for the sides and bottoms, but for the
back you need to be careful.  Many people use plywood for the back to
avoid this problem: plywood is quite stable in all dimensions.

An alternate for plywood for the back is to use thin tounge-and-groove
boards linked together.  Nail these in place so that they can move
with the seasons.  If you are building this cabinet in the drier part
of your year, make sure the boards are spaced out a little so that
when they expand with higher humidity they won't force your cabinet
sides apart.

Another problem: your joinery.  If this piece is going to be put under
any stress, you can do better than a dado or rabbett joint.  These
joints are not very strong because they don't depend entirely on the
glue bond for their strength, but they don't present a lot of face
grain for the glue to stick to.  Gluing end grain just doesn't work
very well.

I would suggest dovetails for the bottom (where your sides and bottom
meet edge-to-edge), and wedged through mortise & tenon joints for the
top (where your side edges meet the face of the top).  These joints
are superior to dado/rabbett joints because they provide both
mechanical strength and more face grain gluing area.

If you don't want to tackle the more complicated joints, you can use
screws.  But, if you use blocks inside the corners, you are
introducing cross-grain glue joints.  The person who suggested this
probably didn't realize you were working with solid wood, or maybe
does not have much experience him/herself with solid wood.  Instead of
using blocks, screw through the top and bottom into the sides.
Obviously you'll have to somehow plug the holes on the top at least.

I would suggest that if you use the dado/rabbett/screw approach that
you also use a plywood back.  A plywood back glued into place will
lend a lot of strength to the cabinet.  If you want to use the
tounge/groove boards (a better-looking solution IMO), you must use
stronger joinery at the corners.

As for finishing, well, each to their own.  But in my house you'd be
harrassed for using a thick polyurethane finish on something like
this.  I would suggest that you experiment with some alternatives
before you finish your masterpiece.

-- 
Doug Bailey
([email-masked])

---

From: "Kurt Blank" <[email-masked]>
Date: 2 Apr 1997 14:01:10 GMT

Douglas Bailey <[email-masked]> wrote in article
<[email-masked]>...
>lots of snip

> >Peter Neil.

Peter,
Very interesting and thorough.  I'm curious though. I live in the Dallas,
TX area and have been working with Oak (red & white) for over a decade. 
I've really never taken the movement of wood seriously and have never had a
piece crack or a joint break.  In the Douglas Bailey scenario I would
definitely screw the top on.  If it's a tall cabinet, I would just scew
>from  the top into the sides and put a plywood back on with tiny nails. 
None of the hardware would be seen.  I've never witnessed a screw coming
loose over time.  Now, I'm only talking about 12 years, maybe I'll see
something happen later on.  I've, also, made posts to this group asking if
anyone has  witnessed a glue joint breaking on a piece of furniture and
haven't seen any replies.  I may have missed them. 

Anyway, I'm still curious if the amount of time and effort some put into
the glueing and worrying about movement is worth it.
Regards,
Kurt

---

From: [email-masked] (Douglas Bailey)
Date: 2 Apr 1997 16:33:18 GMT

In article <01bc3f6e$24848bb0$2a35759c@cna0165254>,

>I've, also, made posts to this group asking if

I can give you one specific example that comes to mind.  I built a
chess board a few years ago.  The squares were maple and cherry, a
little bigger than 1.5"x1.5" glued together with grain running the
same direction.  This made the playing surface a little bigger than
12" square.  Around this I mitred a frame of red oak, glued to the
board.  So I had cross grain on two of the sides of the board.

The glue joints cracked and the board started to come apart after
about 18 months.

Contributing factors:
   - the glue was getting old and was past its shelf life.
   - dry winters and humid summers around here.
   - the board was given to a friend who lived in an apartment
     with electric heat -- this exacerbated the humidity swings

What is Dallas like for seasonal changes?  It might be the case that
your weather is easier on the wood than the weather around here.

Can you give an example of a project you've built with a large
cross-grain joint that has survived for several years?  I'm curious of
the techniques you've used.
-- 
Doug Bailey
([email-masked])