The Handyman's Book of Tools, Materials, and Processes Employed in Woodworking. Paul N. Hasluck
When the teeth are fairly regular and to the form of Fig. 292, top them by laying a second-cut topping file on their points and pass the file along over the teeth from heel to point of the saw. This will bring the teeth uniform in length. Now file every alternate tooth, first on one side and then on the other side of the saw, as shown in Fig. 293. Hold the file as nearly as possible to the same angle in each case, as it is on this filing that the regularity of the teeth depends. When all the flat places caused by the file when topping the teeth disappear, cease filing, as any further filing may cause low teeth, which tend to make the saw run out of truth, and to destroy sweet cutting.
FLAT-JOINTING SAWS.
After a saw has been sharpened, it should be carefully laid flat on its side and the teeth rubbed down with a whetstone or smooth file to remove any feather edge that may be left by the file in sharpening. This gives a larger and better cutting edge to the saw. If the points only of the teeth are allowed to do the work, the action is a scratching and not a cutting one.
Fig. 292.—Teeth ready for Topping.
Fig. 293.—Tenon Saw Teeth.
OBTAINING UNIFORM TOOTH BEVELS AND ANGLES.
One of the great difficulties in hand sharpening is to get the bevels of the teeth exactly alike. A number of mechanical arrangements to guide the saw and effect this object have been tried with more or less success. In one of the best of these devices a circular casting is divided and indexed from its centre each way, giving bevels for each side of the saw, or square across. The file is fitted into a guide, and is held by a set-screw. The index shows the pitch at which the file is set, and a rod passes through holes in a graduating ring and guides the file. The frame upon which the ring is held slides in grooves cut on each side of the vice in which the saw in fixed; a table connected with the guide is arranged and indexed so as to give the required bevel and pitch for the kind of saw to be filed, and it is only necessary to set the ring for the bevel, and the indicator for the pitch, and the apparatus is ready for use. As the filing is proceeded with from tooth to tooth, the frame follows, giving to each tooth on one side of the saw the same bevel, pitch, and size as on the other, thus leaving the saw, when filing is finished, with the teeth all uniform in size, pitch, and bevel, so that each tooth will do its share of cutting equally with the others, thus turning out more and better quality of work with less expenditure of energy. An old-fashioned way of getting the right angle of a tooth of a hand saw in filing is shown by Fig. 294. A hand saw blade is narrowest in width at the point, and broadest at the butt; and the slope of the back, compared wth the line of teeth, is almost always uniform for all saws: and if a square be placed against this back, a tooth may be filed whose cutting edge is perfectly in line with the edge of the square. All the teeth being thus filed and afterwards set, a saw which will answer general purposes is produced, and one which will suit the worker who has but one hand saw. It will cross-cut soft woods and rip hard woods, thus being a kind of half-rip. Moreover, this square may be used as a gauge, the teeth not necessarily being filed as shown; and if the rake or lead be very much, an adjustable bevel may be used.
TIME WASTED BY BADLY SHARPENED SAWS.
It should be borne in mind that the workman who can saw squarely to a line is at least two hours a week ahead of one who, either because his saws are in bad order or because he has never got out of the bad habit of sawing out of square, cannot do it. It may be partly, or altogether, the fault of the saw. If one row of teeth is longer than the other, the longer side must of necessity advance faster than the shorter, and constantly tend to force the saw away from the line. The user, in his endeavour, by main force, to compel the saw to follow the line—that is, by twisting that part of the saw which is for the time being above the wood—cannot yet force the bottom half of the saw, which has to follow the direction given to it by the set of the teeth, and consequently the saw is said to “run.” This continues, and the amount it runs from a square cut is doubled, so that, if the stuff has to be planed square and the saw runs only 1/8 in. in 2 in., this implies that 1/4 in. has to be planed away before the edges can be got to fit the square. This wastes both time and material.
Fig. 294.—Obtaining Correct Bevel of Saw Teeth.
“SET” OF SAW TEETH.
The theoretical aspect of this matter has been dealt with already. After the saw is filed, and all the teeth made as uniform as possible in shape, length, and gullet, comes the important operation of setting the teeth so as to afford a ready clearance for the saw-blade. The “set” consists of the setting over, or bending, of each alternate tooth to one side. The set should be as little as circumstances will allow, on account of the amount of labour it entails in working the saw. For dry, hard, thin wood cut lengthways, a very little will suffice; but for soft, wet, thick, or resinous material, a larger amount of set is necessary to free the saw. This is easily understood when it is remembered that the set causes the kerf, or groove made by the teeth, to be slightly greater than the thickness of the plate, so that the broad surfaces of the latter shall move through the wood with the least possible amount of friction. The blades of the best saws are thinned slightly towards the back, but this does not obviate the necessity for setting. Some idea of the set of a hand saw can be obtained from Figs. 289 and 290, p. 75, which, however, somewhat exaggerate the amount of set. No more set should be given to a saw than is absolutely required, as the more the set the greater the power required to work, and the greater the loss of wood. A saw should have only just enough set to clear itself; if it has too much it is not properly guided by the kerf; it wastes too much wood, and does not cut smooth or easy. If the setting is not uniform, power will be wasted. The longest teeth, having the greatest set, are rapidly worn down, and the work turned out, is scored and rough, and at the same time the saw will run from the straight line to the side on which there is most set. if a saw is properly and uniformly set, the teeth should form an angular groove, easily seen when held up to the light and looked at from point to heel.
Fig. 295.—Saw-set with Blunt End.
Fig. 296.—Saw-set with Pointed End.
Fig. 297.—Saw-set with Gauge.
SPRING-SETTING SAW TEETH.
Two kinds of setting are used for hand saws—namely, spring-setting and hammer-setting. In the former the teeth are bent from the line by a saw-set; in the latter they are set over by a blow from a hammer. First, spring-setting will be described. For this purpose is used a saw-set (Fig. 295), which is made of steel, and has a series of graduated notches cut into each edge. Figs. 295 and