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Andy Dingley

On 29 May 2007 09:55:57 -0700, wrote:

However, I do not know what to do for the
backing ,and I do not want plywood backing on it.

You have two choices: plywood, or lapped boards.

As you probably know, wood shrinks with decreasing moisture. It shrinks
widthways and radially, but not lengthways. A great deal of joinery
isn't just about constructing boxes, it's about constructing boxes that
don't warp or crack when they dry out.

Plywood doesn't shrink. So you can apply it rigidly to the back without
worrying about splitting. This will stiffen up your carcase
substantially. Overall this is the best way to make it -- it's entirely
reasonable to use plywood here. You can of course use a good grade of
veneered cabinetry ply.

If you use solid boards, then you need to deal with them shrinking.
They're width-wise boards (probably the grain running vertically) in a
cabinet built with a top board and shelves that won't shrink when dried
out. So you need to allow for these boards shrinking in service
(assuming you're not building it indoors in a heated workshop!), yetnot
have them split or leave gaps between them.

The usual fix here is to half-lap the boards by cutting a wide, shallow
rebate in the edge of each one and overlapping them. When they shrink,
then move sideways over each other and don't leave a gap. Stain them
before assembly, so that this gap isn't an obvious light stripe.

They're also at risk of splitting, so only fix each board with one nail
at each end (or into each intermediate shelf) and place it in th emiddle
of the board. Also space the boards out evenly.

To accurately estimate shrinkage, read Hoadley's excellent book
"Understanding Wood". It's hard to say how much you might see from
workshop to driest weather, but 5% isn't a bad start. It's about 10%
tops for green wood to fully dry.

Of course fastening the boards with just a single nail means that
they're no longer stiffening the carcase. This is the cost of not using
plywood. You understand _why_ now, so it's your call as to choose which
one.