This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
Both hand filing and machine filing have their advocates. The former is generally more convenient, and may be rendered sufficiently regular by means of guides. The latter gives greater speed and regularity at less cost.
For hand filing, reference has already (p. 193) been made to a clamp for holding the saw. A very old and convenient form is shown in Fig. 306, and consists merely of 2 strips of wood (which may be pine, but hard wood is better), about 3 in. wide and 7/8-1 1/4 in. thick, joined laterally by a wooden screw passing through both at one end, and having their upper outside edges chamfered off. The toothed edge of the saw stands sufficiently high above the clamp to allow the saw to be used in a slanting direction without coming into contact with the clamp. Another form consists of an A-shaped horse, whose standards are hinged together along the top, where the saw is placed and held fast by putting the foot down firmly on the cross bars supporting the legs of the horse. Other forms have been already described under Holding tools. Much of the noise produced in saw filing may be remedied by having a layer of leather, rubber, or a few folds of paper between the saw blade and the jaws of the clamp. There must be no shake or jar in the saw while under operation, or the teeth of the file will be damaged.
To put a saw in order, the first thing to be done is to joint the tops of the teeth, or render them uniform in length. This is termed "top-jointing" in straight saws and " rounding " in circular saws To carry it out, Hodgson recommends the following cheap and expeditious plan. Procure a block of wood, say 6 in. long, 3 in. wide, 1 in. thick, dressed straight and true, then nail a similar piece on one edge, thus forming a corner in which to place a file. The file can then be held with the fingers, or be secured in various ways. Place the file flatly on the teeth, and press the larger block against the side of the saw blade, then file off the points of the longest teeth until the file just touches the extremities of the short teeth. It is important that the file be held in such a position that it will take off the points exactly at right angles with the blade, otherwise the teeth will be longer on one side than the other, which will cause the saw to deviate or "run" more or less. Grimshaw remarks that the operation is generally performed with a flat or " mill " file, although it may be done with a plane emery rubber or a whetstone, " Side-jointing" is the term applied to a process for correcting irregularity in the set, or preventing undue side projection of any tooth; each tooth is thus made to do only its fair share of the work, and scratching or ridging of the sawn surface is avoided.
It is most effective on swaged eeth, and is performed by a side file set in an adjustable clamp as shown in Fig. 307.
Very useful adjuncts to inexperienced workmen are the so-called filing guides, which determine the angle of contact and degree of force with which the file is applied. Fig. 308 shows a simple form, easily worked, and adapted to both straight and circular saws. The saw is held in the clamp a. On the guide is a circular plate b graduated to a scale for setting the file to a bevel for either side or square across the saw. Legs c extend from the plate over the clamp into grooves in the sides of the clamp. On the nether side of the plate b are a number of grooves corresponding to the scale on the edge, and into which a raised rib on the arched piece e mashes, and is held in place by the thumb-screw d on the top of the plate. Through the ends of the arched piece e slides a rod f, to which are secured by screws the arms that carry the file g. By loosening the thumb-screw d, the file is readily changed to any desired bevel, and the handle of the tool may be lowered. When the file is set to the required bevel it is secured by tightening the thumb-screw d, and its pitch is regulated by a set-screw in the socket of the arm at the handle. During the operation of filing, the rod / governs the pitch and bevel, so that every tooth is equally filed.
The machine is adapted for full, hollow, straight-edged, or circular saws. A table is issued with the machine, giving the correct bevels and pitches for the various kinds of saw to be filed.
Fig. 309 shows the Amesbury band-saw filing machine, fastened to an ordinary bench. The file is in 2 sections, one stationary, the other movable in the direction of the axis; the stationary section carries the feeders and a thin segmental file, which files only the gullets and faces of the teeth; the movable section carries a thick bevelled file with varying grades of teeth, rotating in a higher plane, and destined to file the backs and take the burr from the points. The thumb-screw a varies the height of this section to suit the grade of teeth and to change the pressure. The thin face and throat file is cut only on its face and corner. The filing head runs in an oblong bearing, so that it can move to allow for high teeth. An adjustable pressure spring b holds it to the work, and another spring under the head keeps it to the tooth-face, thus giving the high teeth the most pressure, and bringing them down to the general bevel. The saw is held in a clamping-jaw, with the back resting against the gauge c, which is adjustable to any saw width by the screw d, and can be set at any angle. The clamping-jaw is operated by a cam on the hub of the gear, and opens and closes as the machine is feeding or filing.
This jaw acts like a vice upon the saw when the files are in contact with the teeth, and releases it when in contact with the feeder. The filer will work on saws from 1/16. in. to 2 in. in width, and having 2-20 teeth to the inch.
Elkin's patent saw sharpener, Fig. 310, enables any person to accurately and quickly sharpen any straight saw, including rip, cross-cut, buck, band, jig, etc. It is a combination of clamps and adjustable guides, by means of which the saw can be firmly clamped and correctly sharpened. The adjustable guides can be so marked as to give the tooth the same bevel, pitch, and elevation. The machine is simple, strong, and durable in construction, being made from the best iron and steel. It only occupies a space in inches of 16 x 3 X 3. For use, secure it to a bench with 2 screws, place the saw in the clamp, with the teeth just above the face or upper part of the jaws - the handle to the right. The rod, upon which the travelling plate slides as each tooth is filed, can be secured at any desired elevation by means of the thumb-nuts at the ends. Having obtained the elevation, the file is brought across the saw at an angle corresponding with the bevel of the tooth, and there made fast by turning the thumb-screw beneath the travelling plate