The back saw illustrated in Fig. 17 is used as a bench saw for light or fine work, and for fitting and dovetailing. Saws of this type are made from 8 to 14 inches in length, the 10- and 12-inch being convenient sizes for general work. As the metal back holds and stiffens the saw, a thin blade should always be selected. The methods of filing, jointing, and setting are the same as those described for the other hand saws. At least two back saws will be found necessary, one filed for crosscutting, and the other filed as a rip saw for cutting with the grain of the wood, as in the cutting of tenons and dovetails.
Fig. 17. Back Saw.
While for those who have had experience in carpentry the following exercise in the use of the back saw may not be necessary, it is recommended to all beginners who wish to acquire skill in the use of this important tool.
Take any block of wood from 12 inches to 16 inches long, about 2 inches wide, and about 1 3/4 inches in thickness. With try-square and a sharp-pointed pocket knife, lay it out, as illustrated in Fig. 18, on the upper, front, and back sides of the block. The knife cuts must be at least 1/12 inch deep, and about i inch distant from each other. Next proceed to saw up the block into thin sections, sawing each time so that the saw kerf will be just outside of, but close to the knife line, as indicated at a.
The saw cut through the block should be true to each of the three lines; and while the saw passes along one side of the line, its teeth should not scratch the opposite side of the knife cut, but should leave a smooth clean angle of the knife cut on the block, as shown at b in Fig. 18, while at the same time it should be so close to the line as to leave no wood to be smoothed off with plane or chisel.
Fig. 18. Example of Back Sawing.
A few hours' thorough and careful practice of this exercise will enable any one to use the saw successfully.