"[p]lenty of scope for improvement still exists, especially in saws of stout gauge and considerable width -- say, above 3 inches. Wide band saws are valuable for certain classes of heavy bevel sawing, such as the curved forms required for ships' timbers or the backing for armour-plated vessels. Their use for these purposes, however, is much retarded, owing to the heavy loss sustained even by the breakage of a single saw, as when once broken it is a matter of considerable difficulty to braze efficiently wide saws of stout gauge.
In 1856 Mr. W. Exall took out a patent for improvements in the manufacture of band-saw blades. These improvements consisted chiefly in heating the blade by means of blow-pipes or lamps whilst it was being passed through the rollers or dies used for the purpose of reducing the blade to its proper thinness, and in giving the blade its proper temper by continually rolling it between hard rollers or by repeated drawing through dies, as in drawing wire. He also claimed another plan of tempering the blade when joined ready for work by heating it in a suitable oven and then plunging it into oil or other fluid.
A patent for an improved machine for setting the teeth of band saws was taken out by Mr. L. Orton in 1876.
In this invention two pulleys hold the saw taut, and the two limbs of a forked frame suspended on a short shaft carry each a punch, that operates, as the frame is oscillated by the handle, to set the teeth from opposite sides, the saw being fed along by a pawl on a bell-crank lever, that is actuated by a cam fixed upon the frame.
For sawing very hard wood or iron the teeth should be made shorter, and with at least one-third more points to the inch, than in blades for sawing soft wood, as they will stand little or no setting; for a clearance for the saw they are made to taper from the points of the teeth to the back of the saw. The teeth of band saws should be set by blows in preference to bending, which, unless very carefully performed, is more liable to buckle the blades and prevent them running true.
Saw blades of too hard a temper, where the steel has crystallised, or where the blades have been subjected to imperfect or sudden tension, break readily, the fractures usually commencing from the roots of the teeth. A good saw-blade should be elastic in its temper, without hardness; the gauge, width, and toothing should be uniform throughout. Care should be taken in jointing the saws that they are not made thicker at the braze, as when in work, if this is the case, they will be found to jump and not run true on the saw wheel, breakages being the result. The operation of brazing or jointing band-saw blades with a little practice is easily performed. The modus operandi is as follows :
Take each end of the blade and file down a taper on the opposite sides of the saw of about three teeth points, so that when the two ends of the saw are made to overlap each other the joint, when cleaned off, will be the same thickness as the rest of the blade. Secure the overlapping ends of the saw well together by small hand vices, and tie them with fine iron wire. Over this bind tightly with brass wire the full length of the overlap. Moisten the joint with water and cover it with powdered borax. Either take a large tongs and make it red hot, or place the saw in a small forge fire made of charcoal and keep it there till the brass is well melted. Let the saw cool gradually, and file the joint to the same gauge as the rest of the blade and finish it with emery cloth. If this operation is well performed the joint will scarcely be distinguishable. Some prefer to moisten the saw with diluted muriatic acid, we presume to remove any grease; but we have always found plain water answer very well. Care must be taken that when brazed the overlapping ends of the saw press well together.
It is difficult to distinguish by inspection the quality or temper of a saw blade. A blade either too soft or too hard is comparatively useless. By bending the blade you can in a degree judge by its elasticity as to its temper, but users must, however, necessarily be more or less in the hands of the manufacturer.
The expansion and contraction of the saw blade is a fruitful cause of breakages. This can be somewhat lessened by lubricating the blade well, keeping the leathers on the saw wheels true, and slackening the tension of the saw immediately after finishing work. The bed plate and column of the machine should be of sufficient section and area, and fixed on a foundation of sufficient firmness to prevent any jar or vibration even when sawing the heaviest timber of which the machine is capable. We have found saw blades of a thin gauge to stand better than stout ones. They should always bend easily over the pulleys, as if the angle is too sharp for the gauge or temper of the saw they will invariably break.
Although we are aware they are thinner than those usually employed, after considerable experience we can recommend the following thicknesses of saws as the gauges most suitable for sawing pine and the softer kinds of wood of the Pinus family. The lengths of the blades are given in feet, and the thicknesses by Birmingham wire gauge :- 
We give herewith illustrations of the saw teeth we have found most suitable for band-saw blades for cutting all ordinary classes of wood. Figs. 43 and 44 are well suited to most of the woods of the Pinus family, except pitch pine; for working this wood we can recommend fig. 45, the teeth of which should be coarsely spaced and set. In addition to this, owing to the clinging properties of the resin, a, small brush should be attached to the machine, so arranged that the saw blade is constantly swept by it; an occasional application of grease to the blade is also an advantage, as the resin is more readily removed. We can recommendfor durability saws with gullet teeth--i.e. teeth rounded out at the root, similar to figs. 44 and 47-as they are much less likely to fracture in working than saws with the roots running to an angle, as the fracture in the blade is found almost invariably to commence at the point of this angle. Owing, however, to small gullet teeth being more troublesome and expensive to sharpen, the angle teeth are still more generally employed.
After several experiments we have found the teeth shown by fig. 46 very suitable for sawing oak, ash, elan, and other hard woods, and by setting the face of the teeth farther back-i.e. slightly out of the perpendicular-the cutting action is improved.
These figures must not, however, be considered as arbitrary, but can be modified according to circumstances. The smaller the diameter of the saw wheel, so should in ratio the gauge of the saw be reduced. This, however, does not apply to those machines of the smaller class in which the saw blade runs over three wheels instead of two, as in this case the blade does not impinge on the, periphery of the saw wheel at so sharp an angle as when two wheels only are employed.
For cutting the harder and closer-grained woods, such as oak, beech, &c., the thickness of the saw should be increased about one gauge, the teeth should be more upright and spaced finer, and the set also should be reduced. For woods of a woolly fibre, such as English poplar, the teeth of the saw should be of coarse space and set, to effect a clearance and overcome its clinging properties. For cutting metal the thicknesses given may be increased about three gauges, the teeth of the saw being very finely spaced-say, twenty points to the inch-and set slightly with a hammer. These saws are made to taper towards the back of the blade for clearance.
For heavy curved sawing, such as the timbers used in ship-building, the backing of armour-plated vessels, &c., for all saws above 24 inches wide we can strongly recommend the gullet tooth, as shown in fig. 47. In fig. 48 are teeth adapted for cutting iron and metals ; they should, however, be somewhat stouter at the root than those shown in sketch.
The figures are not drawn to scale, but are intended to illustrate the shape or form of the teeth.
|
Writing in 1880, M Powis Bale -- considered both at the time and by scholar's today as an authority on woodworking machinery technology -- argues that, in the creation of bandsaw blades, "recent advances" -- primarily in France led to impoved bandsaw blade [operation]" not so much from the quality of the steel employed, but more likely from advanced method employed in tempering, "which ensures to the blade a considerable amount of hardness combined with toughness". The manufacture of these saws on an extensive scale has never been carried out in this country, the method of tempering successfully 'being kept more or less a secret. 
