On 1 Oct 2004 18:30:51 -0700, (ississauga)
wrote:

When I see large pieces of finished lumber, say a piece of 1" thick
oak thats a foot by 4 feet, it seems to be made of several pieces
joined together.

This is very common, although I'd be a little surprised to see oak
treated like that, in those sort of sizes. There are several reasons
to do it.

It's done for several reasons. Go to Ikea and look at their "solid
timber" products. These are nearly all thin strips of rubberwood
glued together, no more than an inch or two wide. Rubberwood is a
popular timber these days because it's sustainable (and not a bad
timber). When trees on a rubber plantation are worn out, they're now
felled for timber. They're only small though, so they must be joined
together to make a useful board.

In foot-wide oak, then you don't need to do this. Oaks are quite large
trees and sawn boards will already be this sort of size. You can buy
solid one-piece oak quite easily.

The problem with oak is that of timber movement. If you cut any
flat-sawn board, it tends to curve on drying - the rings in the tree
tend to go straighter.

One solution is to only use radial boards, which don't curve. In
medieval times this was done by splitting the tree rather than sawing
it (also easier work) to give very stable "riven" boards,
unfortunately wedge-shaped. Around 1900, the fashion was for
quarter-sawn oak timber, where consistent flat boards were sawn as a
good approximation of being radial. This is expensive sawing work,
because you need to keep turning the log round for each new cut, and
also because there's more timber lost as waste.

So if you're looking to build non-warping furniture from flat-sawn
oak, the usual solution is to saw the board narrower, then put it back
together. This would usually be done in the workshop though, not at
the timber yard. Boards are re-assembled either in the same order, or
more usually alternated up and down, so that any small warp that does
form becomes an even smaller "wiggle" instead. The width of the
boards used depends on the application, the thickness and the quality
of the timber. Boards flat-sawn from near the centre of a log are
comparatively stable (they're almost quarter sawn anyway), those near
the surface are less so.


For joining them, then it's done with glue. It's a long joint of the
long-grain face of the timber, so it's a strong join. Commercially
(Ikea) it's done by a huge machine. Commercially (small furniture
workshop) it's done by a manual clamping jig called a "panel press"
(search for "Plano", as the best-known maker). If you wish you can
also do it with biscuits. Biscuits add little to the strength, but
they make alignment easier if you only have bar clamps to hold it
together and not the alignment abilities of a press.


If you want to know more, any cabinetry book will tell you, or I
recommend Hoadley's "Understanding Wood" or the US Government Forest
Products handbook (paper copies available from Lee valley, or read it
as free PDFs on-line)
--
Smert' spamionam