Experiments have shown that timber beams having the annual rings parallel to their depth are stronger than those which have the rings parallel to their width. Thus, in the log shown in Fig. 164 the piece cut from A will be stronger than that cut from B. Again,the purpose forwhich the timber is intended should be borne in mind. Thus, in preparing floor boards, care should be taken that the hearts should not appear on the surface of the finished board. If they are allowed to do so, as in Fig. 165, the central portions will soon become loose, will be kicked up, as shown in dotted lines, and will form a rough and unpleasant floor.
When planks which have shrunk to a curved form have to be used to form a flat board, they are sometimes sawn down the middle and glued together, the alternate pieces being reversed as in Fig. 166; thus the curvature in each piece is so slight as to be almost inappreciable, and the reversal of the alternate pieces causes each to be a check upon the shrinkage of its neighbours.
There are several methods of converting oak described in Gwilt's Encyclopaedia of Architecture, from which the following is taken; Fig. 167 being very slightly modified. The log is first cut into four quarters.
Each quarter may then be converted in either of the following methods: -
The best method is shown at A in Fig. 167, "in which there is no waste, as the triangular portions form feather-edged laths for tiling and other purposes."
This method also cuts very obliquely across the medullary rays, and thus exhibits well the silver grain of the wood, which is so much admired for cabinet work and other ornamental purposes.
The next best method is at B. The method shown at C is inferior to the others; that at D is the most economical where thick stuff is required.
A good practical method adopted for cutting oak logs so as to get wide boards is to cut all the boards parallel to the same diameter, but leaving the heart to be used for quartering. See Fig. 167a.
At the great saw-mills in Sweden and Norway each log is carefully inspected before it is sawn, to find out how many of the most marketable sizes can be made out of it. Thus if 4-inch deals are in demand, or battens, they will arrange so as to cut more of these sizes, and fewer of the regular 3-inch deals, and vice versa.
Two methods are shown in the accompanying figures, taken from
Mr. Britton's work upon Dry Rot.
Fig. 168 shows an arrangement generally adopted at the present time.
The 9x3 inch deals go into the English market; those 9 x 11/4 inches into the French market.
Fig. 169 shows the method that was adopted until the French market improved. It will be observed that the centre deal would include the pith, and it is in such a case subject to dry rot.