cketbook_, pp. 221, 230.

Coverings.
Sickels, pp. 128-131.
Goss, pp. 141-144.

[Footnote *: For general bibliography see p. 4.]

CHAPTER IX.

PRINCIPLES OF JOINERY.[11]

[Footnote 11: Professor Rankine's Five Principles:

1. To cut the joints and arrange the fastenings so as to weaken the
pieces of timber they connect as little as possible.

2. To place each abutting surface in a joint as nearly as possible
perpendicular to the pressure which it has to transmit.

3. To proportion the area of each surface to the pressure which it
has to bear so that the timber may be safe against injury under the
heaviest load which occurs in practice, and to form and fit every
pair of such surfaces accurately in order to distribute the stress
uniformly.

4. To proportion the fastenings so that they may be of equal
strength with the pieces which they connect.

5. To place the fastenings in each piece of timber so that there
shall be sufficient resistance to the giving way of the joint by
the fastenings shearing or crushing their way thru the timber.]

1. _Avoid multiplication of errors by making all measurements (as far
as possible) from a common starting point, and laying off all angles
from the same line or surface._ Illustrations of this principle are
as follows: Before proceeding with other processes, a working face and
working edge and as many other surfaces as will finally appear in
the finished piece, should be trued up. At least the working face
and working edge are essential to the proper "lay-out" of the piece,
whenever measurements are made from an edge.

In laying out a series of measurements, it is important, when
possible, that the rule be laid down once for all, and the additions
be made on that, rather than that the rule should be moved along for
each new member of the series.

In scoring around a board with knife and try-square, the head of the
try-square should be held against the working face in scoring both
edges, and against the working edge in scoring both faces, and not
passed from one surface to another in succession.

In the laying out of a halved joint, Fig. 265, Nos. 15-19, p. 178, the
gaging is all done from what will be one of the flush surfaces of the
joined pieces. Then, if the gaged line should be slightly more or less
than half the thickness of the pieces the closeness of the joint would
not be affected.