This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Fig. 25 shows a set of saw blades which are intended to be fastened in turn to the same handle and used for various purposes. These blades are very thin and can be used for cutting out small holes such as keyholes, and it is for this reason that such saws are called "keyhole saws." The teeth are in general similar to those of the back saw, but are usually smaller.
Great care must be exercised in the filing of a saw, to give it the proper "set" to enable it to do the work required of it, and this work is better left to an expert. Most carpenters, however, like to know how to file their own saws and to keep them in good condition. A great deal has been written on this subject both in books and in trade papers, but it is almost impossible to describe, in writing, the proper methods. It is a part of the carpenter's trade which must be learned by experiment and by watching the older workmen.
Fig. 24. Slope of Teeth of Back Saw.
Fig. 25. Keyhole Saw with Detachable Blades.