Sawing Machines

SAWING MACHINES. The saw is one of the most valu able tools, and just as there are many varieties of hand-saws so there are many machines, suited for sawing wood, bone, fibre, stone, marble, slate and metals, and varying in size from little fret-sawing machines to the huge machines which part off steel ingots with a 12 f t. diameter circular saw.

There are three methods of action; the reciprocating blade, cutting one way or both ways, the continuously running blade or band-saw, and the circular saw. Some materials can be cut on any system without making any real difference to the results, but often it happens that one method proves better than an other. The shape to be parted off or cut to outline may be diffi cult or impossible with one sort of blade and easy with another, while size makes a difference in some cases. Thin saws penetrate with less consumption of power, and are the choice if they will cut truly instead of deviating. Moreover, there is less waste of material in the form of dust, an important consideration in the more expensive substances. Yet if a thin saw wanders from a true line it may not be economical, by reason of the fact that the cut surface has to be trued up afterwards with more or less expenditure of time and labour. Wood cutting saws are dealt with under WOOD-WORKING MACHINERY.

Machines with Reciprocating Blades.

The smallest machines of this class are the jig-saws, equivalents of the fret saws for wood. The work is held upon a horizontal table up through which the saw blade reciprocates, with a stroke variable from zero to three or four inches in the smallest sizes. Dies, metal patterns and templates of intricate outline are sawn out of sheets or blocks. The reciprocation is produced by a belt pulley driving a crank-disc and connecting-rod. Some machines have holders which will grip a file instead of a saw so as to finish outlines smoothly after sawing, and an oil-stone stick or lap may also be used for truing up hardened dies.

A larger type of machine is the power hack-saw, which has a horizontal frame to strain the blade in like a hand hack-saw; it reciprocates the blade with crank and rod over a vice in which the bar or girder to be sawn is clamped. The weight of

the frame is sufficient to feed the blade through, and a safety arrangement takes care of the possibility of the blade snapping as it breaks through the bar. Multiple-blade machines cut off a number of discs or slabs simultaneously, and rather big machines are now made for girder sawing. Portable machines are used for sawing tram and railway rails and girders. The hack-saw is a cheap and handy machine for any class of work shop, large or small, and the blades are cheap and quickly replaced. Until recently they were thrown away when worn too dull for efficient cutting, but now tungsten blades of fast cutting capacity can be sharpened many times.

Band-Sawing Machines.

Wide cuts are taken in wood with reciprocating saws that deal with logs, and stone-sawing machines are also built on the same principle, a long table carrying the wood or stone along under the blade, but this is not suitable for thick metal-cutting. The band-saws cut faster, with better guidance, and the dust is carried away more effectually. These machines are either vertical or horizontal. In the former design the metal is clamped to a horizontal table and the blade runs over a top pulley and down through the work and table to the lower pulley. Straight or curved cuts are controlled by the movements of the table by handles and screws operating slides. Though small machines are occa sionally used instead of the jig-saws, most band-saws are of fairly large dimensions, with pulleys from 3 ft. to about 6 ft. in diameter, the latter size admitting slabs or forgings of nearly 6 ft. in depth. The pulleys are covered with rubber tyres to give the grip to the saw, and in cutting iron and steel a soapy water solution has to be pumped on to the blade. This is run through a guide immediately above the surface of the work to assist in true cutting. Horizontal band-saws of large dimen sions deal with forgings, fed along by a table as in a planing machine, and are also very convenient for trimming off the uneven edges of flanged plates, for boiler construction, enabling the caulk ing to be done properly after riveting together.