BORING BIT. A tool or instrument used for making aper urea in wood, metal, or other hard substances. They are of various shapes, too common to workmen to need description ; but one of a very peculiar and effective kind, represented above, was brought from Germany by Mr.Donkin, and is described in the Tramactions of the Society of _Ms. Fig. 1 is a front view of the boring bit; a a the cutting edge ; b b a thread or fin, winding round the back, which acts as a screw to draw the bit into the wood. Fig. 2 is a side view of the same. The instrument is very simple, enters the wood rapidly, and forms a clean hole. BORING MACHINES. A name usually confined to machines for giving a perfect form to metallic cylinders, as pump barrels, blowing machines, &c., which machines differ from lathes in the circumstance of the tool revolving, whilst the work either remains stationary, or advances in a right line. In all boring machines, a long bar, called the boring bar, passes through the cylinder, and revolves in bearing or supports. To the boring bar are fixed a number of steel cutters, which, as they revolve, receive also a motion endways, and are carried through the whole length of the cylinder to be bored. The boring machine used for the smaller and coarser description of pump work is extremely simple in its construction. It consists of a boring bar, somewhat more than double the length it will ever be required to bore, and supported by bearings distant from each other not quite half its length. A mortise is cut through the boring bar, and the cutters are firmly fixed in it by wedges or keys. Into a socket in one end of the bar is keyed a screw about half as long as the bar, and its outer extremity supported in a nut fixed in a standard, the axis of the screw and of the bar exactly coinciding or forming a continuous right line. The bar being passed through the cylinder to be bored, and the cylinder being secured upon beds so as to be concentric with the bar, the latter is turned round either by a winch or a wheel, fitted upon the end opposite the screw ; and the screw making a revolution in its nut for each revolution of the bar, advances the bar and cutters through a corresponding space along the cylinder. For cylinders of larger diameter, and requiring more accuracy in the boring, a different construction becomes necessary. The cutters are fixed upon the cir cumference of a short cylinder, termed the cutter-block, through which the boring bar passes; and either the two, as they revolve together, receive a slow end motion, or the cutter block only advances whilst the bar revolves, but remains stationary. There are various modes of advancing the cutters in either case. The following extremely ingenious arrangement, in which the boring bar and cutter advances, carrying with it the cutter block, is, we believe, the invention of Mr. Murray, of Leeds. Upon the extremities of a horizontal bed of cast iron are fixed two upright standards, supporting brass bearings, in which the boring bar turns. Upon the cast iron bed are two blocks, for supporting the ends of the cylinder, with arrangements for adjusting it, so that its centre shall coincide with the axis of the boring bar, and to these blocks the cylinder is firmly secured by straps or chains. The boring bar is turned perfectly cylin drical, and has a groove extending from one end more than half its length. The cutter block, which is a disk nearly of the same diameter as the cylinder, and armed at the circumference with a number of steel cutters, is firmly keyed upon the bar in the space lying between the standard. Upon the grooved end of the bar, and close to the outer face of the standard, is the driving wheel, the centre of which is bored of the same diameter as the bar, so as to allow the latter to slide within it freely, but without shaking, whilst the wheel is prevented from turning without causing the bar to revolve, by means of a steel key, fitting into the groove in the bar, and into a similar groove in the boss of the wheel. A screw, half as long as the bar, is supported at the outer end by a nut, which is at liberty to turn in bearings placed upon a vertical standard, whilst the inner end of the screw, formed into a square, is keyed into the end of the boring bar.
Parallel to the screw is a small shaft, having at one end firmly fixed a small wheel geering into another small wheel fixed upon the face of the nut, whilst another wheel, which turns with the shaft, but is at liberty to slide along it, Beers into a wheel fixed upon that end of the bar to which the screw is attached. The operation of the machine is as follows : The driving wheel turns the boring bar, and with it the screw. Now if the nut were to remain at rest, the screw would advance through a space equal to the rake of the screw, and draw after it the boring bar ; but if the nut, by properly proportioning the diameters of the small wheels, revolve in the same direction as the cutter bar, but with a less velocity, then the cutter bar and screw will advance through a space proportioned to the difference between the velocities; so that if the speed of the cutter bar exceed that of the nut by one-tenth, the screw and cutter bar will advance through only one-tenth of the rake of the screw. In the boring machines for cylinders of very large dimensions, the cutter block usually advances, whilst the boring bar remains stationary. In these machines the boring bar is sometimes placed horizontally, but we think a vertical position preferable, as the weight of a long horizontal bar occasions a tendency to sink in the middle ; also when the bar is vertical the cylinder is more easily fixed, and the borings, instead of clogging the cutters, fall upon the base plate. The annexed engraving represents a vertical boring machine of a new and improved construction, which was erected in an extensive enifineering establishment, and of which we believe no description has yet appeared m print. Unon a foundation plate a are bolted three standards, of winch only two b c are shown, the third being removed to show the boring bar. These standards support the top plate d, formed of three radiating arms ; a is a steadying bridge, which may be set at any height, by means of screws passing through the mortises in the standards, and secured at the back by nuts ; f is the bed to which the work is bolted, for which purpose it has a number of mortises radiating from the centre ; it is supported by brackets g g projecting from the standard; A is the boring, turning in collars in the top plate d and in the bridge e, and supported by the step i ; k the cutter-block, which is a stiff wheel, bored out accurately to receive the boring bar, so as to slide upon it easily, yet without any shake. On the periphery of the block are eight notches, in which the cutters are fixed by wedges ; 1 a bevelled wheel, and m a pinion by which a rotatory motion is given to the boring bar and cutter block, the latter being made to advance along the former by the following means : Upon the top plate d is a small triangular frame a, to which is bolted the bevelled wheel o, in which another wheel p geers. p revolves in bearings fixed upon the head of the boring bar, and has upon its axis an endless screw driving the worm-wheel g, which is fixed upon a long screw r, lying in a mortise cut in one side of the boring bar. This screw turns in collars a and t, and works in a nut fitting into the mortise in the boring bar, and attached to the cutter block at o; the bevelled wheel p is 10 inches in diameter, and the wheel o 16 inches ; therefore in ten revolutions of the boring bar, the wheel p will perform sixteen revolutions on its axis, and at each revolution the endless screw upon its axis will move the worm wheel q one tooth forward ; and as the worm wheel has sixteen teeth, in ten revolutions of the boring bar the screw r, to which the worm wheel is attached, will make one turn, and will advance the cutter block through a space equal to the space between the threads of the screw. x is a strong spindle screwed into the frame n, and formed with a conical point, which is received into a conical steel bush in the centre of the head of the boring bar, and prevents the bar from rising.