In the case of teeth of coarse pitch, however, this would entail too much labor in filing, and furthermore, as the height of the teeth increases with the pitch or distance apart of the teeth of circular saws, and as the higher the tooth the weaker it is, therefore coarse pitched teeth are given round gullets so as to strengthen them as much as possible. The gumming of a saw should always be performed before the sharpening, and the sharpening before the setting.
When the sharpening is to be done with the file, the cutting strokes of the file should be in the same direction as the teeth lean for the set, as this leaves a sharper cutting edge, and it follows that the proper plan is to file every other tooth first, going all around the saw, and to then turn the saw around in the vise, and file the remaining teeth.
The height of the teeth and the diameter of the saw will be best maintained by filing the front face of the tooth to bring it up to an edge, but in filing the front face the spacing of the teeth should be kept as even as possible.
If the front face has been filed until a tooth is as widely spaced as those already filed, and the edge is not brought up sharp, then the edge may be brought up by filing the back of the tooth.
Fig. 3083.
A saw gumming, gulleting or chambering machine to be operated by hand, and constructed by Henry Disston & Sons, is illustrated in [Fig. 3083]. It consists of a frame spanning the saw, and having screws b b, b b, to adjust to the saw thickness; 4 and 5 are two saw teeth, and 6 the cutter, k is a wheel for the feed screw g, and c and d gauges for regulating position and depth of the gulleting.
The cutter 6 is driven or revolved by means of the handles h h, but an important point in the construction is, that a pawl and ratchet wheel is used to drive the cutter, so that if the handles h h were revolved in the wrong direction, the cutter would not be revolved. This saves the cutter teeth from breakage. The machine is operated as follows:
Run the cutter back by means of screw g as far as necessary, then place the machine on the saw, with the cutter close up in the chamber of the tooth to be gummed.