In the present section, it is proposed to describe the principal points of construction in large circular sawing-benches, such as are in general driven by steam power, and used for various manufacturing purposes. Some remarks are first offered on the conditions and proportions of the circular saws themselves, and the subsequent matter is arranged under the sub-divisions employed in the last section and enumerated on pagg 752.
1. Conditions and proportions of circular saws. - It appears to be uncalled for to enter into particulars on the manufacture of circular saws, especially after the remarks already offered (pages 683 - 698 of this Volume,) on the modes of constructing, sharpening, and setting rectilinear saws, as the methods are nearly similar for both kinds; and some remarks on the circular saw in particular, are given on the first and last of the pages quoted.
As regards the methods of hammering and blocking circular saws, to give them the right degree of flatness and tension, a point of considerable importance, the reader is referred to the section, "On the principles and practice of flattening thin plates of metal with the hammer," (vol. i., p. 414 - 422,) and particularly to the remark, (p. 419 - 20,) on the propriety of keeping the edge of the saw "rather tight or small" prior to its being set to work. So that the heat communicated to the edge in the course of work may, by stretching the edge, render the blade tense alike throughout,- whereas had the saw been at first rather large or loose on the edge, the expansion at that part would render it so loose or flaccid on the edge, as to cause it to vibrate when at work, which is a great disadvantage.
The teeth of both circular and rectilinear saws have been considered at some length, both as regards their outlines, (pages 683 - 687,) and in respect to the modes of sharpening and setting them (pages 688 - 698), but on the whole it may be said that the teeth of circular saws are more distant, more inclined, and more set, than those of rectilinear saws.
The teeth of circular saws are more distant than those of straight saws, because their greater velocity causes the teeth to follow in such rapid succession, that their effect is almost continuous; the distance is carried to the extreme in Mr. R.Eastman's circular saw,