Fig. 35.
For instance, if you were to put cleats on one side of a drawing-board three feet wide, and were to firmly glue the cleats for their whole length (Fig. 35),—you sometimes see such things done,—you would probably not have to wait many weeks before you would hear a report like a toy pistol, and the cleats would be loosened for at least part of their length, because of the expansion or contraction of the board. Similar cases are continually occurring. In such cases the cleats should be screwed, the screws having play enough in their holes to allow for the changes in the board (see [Appendix]).
You must also make plenty of allowance for planing down edges and surfaces and for the wood wasted by sawing. No rule can be set for these allowances. If you do not leave enough spare wood, the pieces will finally come out too small. If you leave too much you will increase the amount of planing or shaping to be done, but of the two extremes it is better to err on the side of allowing too much.
A rod (any straight stick), say six feet long, and another ten or twelve feet long, with feet and inches marked, are very handy to have when laying out work roughly, or for measuring outdoor work approximately.
Lay out your work from only one edge or one surface of a piece of lumber unless you are sure the edges or surfaces are exactly parallel. Having selected the best edge for a "working edge" and the best surface for the "face," mark them with an X or other mark to avoid mistakes (Fig. 36). This is quite important in laying out a number of pieces, as before the stock is accurately worked into shape you cannot usually rely on the edges being parallel. One mark like a V as shown in Fig. 36 will indicate both the working edge and the face.
Fig. 36.
Estimating.—You must, of course, learn to make your estimates yourself, often a very important preliminary. Prices vary, and you cannot always rely on other people's estimates for your own work. It is a matter of simple arithmetic and of making correct allowance for waste and incidentals.
You can always get the prices easily. Figure the amount of wood required, the number of square feet (see page 47) of each kind, or running feet, as the case may be, and multiply by the price a foot; but after this comes the allowance for waste, etc., which cannot usually be figured exactly, but must be estimated.