The woodworker soon discovers that arithmetic is a very practical
and necessary subject. He will meet many problems both in drawing
and in actual construction which test his ability and call for some
knowledge even of elementary geometry. It is important to be able to
estimate from his drawing just how much lumber will be needed. He will
soon discover through intercourse with dealers in lumber that there
are certain standard sizes, and he should make his designs as far as
possible conform at least to standard thicknesses.
Common boards are sawed 1 inch thick. When dressed on two sides the
thickness is reduced to 7/8. In planning some part of a structure to
be 1 inch thick it is better to make the dimension 7/8 inch, else it
will be necessary to have heavier material planed to 1 inch and the
cost will be that of the heavier lumber, plus the expense of planing.
In buying 1/2-inch dressed lumber, very often inch boards are dressed
down to the required thickness, and the purchaser pays for 1-inch
wood, in addition to the dressing. The boy is surprised to find that
it costs more for 1/2-inch than for inch material. Standard lengths
are 10, 12, 14, 16, etc., feet. Widths vary, and as wood shrinks only
across the grain--with one or two exceptions--this dimension cannot be
depended on, as the amount of shrinkage depends somewhat on the age
after cutting. Whenever possible, it is wise to go to the lumber yard
and select your own material, choosing boards that are free from knots,
shakes, etc. Clear lumber--free from knots--costs more, but is worth
the difference.