Fig. 3130.
If as in the case of fine pitched teeth, the teeth are filed with a triangular or three square file but little front rake or hook can be given, without pitching the teeth widely. This is shown in [Fig. 3130], in which s, is the section of a saw, and f, a section of a three square file. The front faces have no rake, and the file is shown as acting on both faces.
Fig. 3131.
In [Fig. 3131], we have the same pitch of teeth, but as the file is canted over, so as to give front rake or hook to the tooth, the tooth depth is reduced, and there is insufficient room for the sawdust. In order, therefore, to give to the teeth front rake, and maintain their depth while keeping the pitch fine, some other than a three square file must be used.
The principal defect of the band saw is its liability to break, especially in band saws of much width, as say 3 inches and over. A saw that is 6 inches wide will ordinarily break by the time it has worn down to a width of 4 inches. Now for heavy sawing it is necessary that wide saws be used, in order to get sufficient driving power without over-straining the saw.