1032
THEORY AND PRACTICE OF ENGINEERING.
Book II.
A. Sills. D. Cylindrical axis. L. Cylinder to be bored. N. Pinion.
B. Frame. E. Iron supports. M. A rack. P. Weight.
rack is moved by the teeth of a small pinion, and maintained in its place by a roller under-neath it, both axes of which are supported by the iron framing.
By means of a lever put upon the square end of the axis, winch is loaded by a weight,the pinion is turned round, giving to the cutter a constant tendency to draw through thecylinder. The axis on which the cutter is placed revolves, and the accuracy of the machine,depends upon its being truly turned, and on the centering of its pivots and gudgeons.
There are several varieties of boring machines and other contrivances for drawing thecutter through the cylinder : one consists of four wheels, one of which is fixed at the right-hand extremity of the bar; another pinion takes the place of the rack, on which is a screwworking in a female screw fixed to the cutters : below the second pinion is a third, fixedon a horizontal axis parallel to the long bar, and having the same number of teeth ; afourth pinion is placed at the other end of the axis, and is driven at the end of the hollowaxis. The first pinion has twenty-six teeth, the fourth thirty, and the second and third
L
K K. Cutter heads. L. Wedges. /,/. The cutters.
Fig. 1582. CUTTER OF BORING MACHINE ,
the same number: as the axis revolves, the first pinion fixed on its extremity drives thefourth, which by means of the third fixed on the same axis with it gives motion to thesecond ; the second pinion being fixed to an axis within the other unscrews the screw atthe other extremity, and advances the cutter along the cylinder: this screw’ has eightthreads in an inch : sixty turns are consequently required to cut an inch.
Some care is required in fitting the cutters, which arc secured by w’edges, and adjustedby turning the axis round, to see whether they describe the same circle ; the boring com-mences by putting the axis in motion, and the machine then requires no further attentionthan observing if the w r eight is lifted up as often as it descends by the motion of the cutters fwhen the cylinder has been once passed through, they are again set to a large circum-ference, and proved the second time, and so on until the boring and polishing is complete.
During the last few years great consideration has been paid to the manufacture of everykind of tool that could perform the work of the mechanical engineers, with more imme-diate effect and economy of time than could be produced by mere manual labour; all thesetools or rather powerful engines, used for the construction of others, are admirably described,accompanied with engravings sufficiently large to explain all their parts and proportions,in an edition of Buchanan’s Millwork, edited by Mr. George Rennie : this elegant work,containing also practical and very valuable observations on the sharpening of tools byMr. James Nasmyth , should be in the hands of every engineer ; the latter w’riter, in anessay in the appendix, shows us most clearly that in forming and setting a cutting tool, sothat it rightly performs its work, it is necessary that it be so placed that its end formsthe least possible angle with the surface to be cut; it must consequently be nearly parallelwith the face or plane it is to act upon
The workshop of the engineer at the present day contains machinery of the most costly