Inventions.
It has been observed and regretted by a well-known writer, that “a periodical work resembles a public carriage—which must depart at the usual hour, whether full or empty;”—and having undertaken to deliver this work at stated periods, I have found myself in a situation not unsimilar: the consequence of which has been a too cursory view of some of the subjects. I feel however, that this is not a sufficient apology for any essential defect: nor would it be more so to say that, although verging to old age, I am still a young author. Yet I may claim the privilege of supplying, in the latter parts of the work, what is most deficient in the former; and thus of proving that I do not intentionally neglect any thing that might make it practically useful.
With these views I commence this third part: intending first to continue the description of the Cutting Engine given at [page 121], and here applied to Bevil Wheels; and then to re-consider, shortly, one or two other objects, that were too rapidly passed over in their proper places.
[Plate 22], repeats at [fig. 1], the [first figure] of [Plate 15]; by way of shewing the additions required to extend this method of cutting teeth, to Bevil Wheels. These additions are first, a disk n n, concentrically fixed to the main axis A B of the engine. And, second, an inclined plane o, of variable obliquity, connected by a joint with the forked sliding bar p q, by which the plane o is put in contact with the disk, at whatever distance the cutter-stand e f may be from the common centre, which distance depends, of course, on the diameter of the wheel to be cut; and to secure which is the office of the fixing screw r, in the figure.
It is now evident that for the disk n n, and the shaft A B to rise, the slide p q and the cutter-stand e f must recede: and this more or less according to the degree of obliquity of the inclined plane o, that is according to the slope of the bottom of the teeth in the wheel w: see the dotted line w p.
A circumstance presents itself, that should be here explained: when the bevil of the wheel w, or the cone of which the wheel is a part, is very obtuse, the cutter-stand e f, can not be driven back by the action of the disk n n on the plane o, without too great a stress being applied from below, to the axis A B. (See the apparatus I M O N, [Plate 16], [fig. 2].) In this case therefore, the handle R is not used: but a weight is suspended to the end N of the lever M N, sufficient to give the whole System A B, a tendency to rise; and the operator now acts on the screw g, so as to draw back the plane o; by which motion the disk m n with it’s axis A B is suffered to move upward, and the wheel is cut, as desired. But on the other hand when the wheels are portions of acute cones, they are cut by means of the aforesaid handle; by which the plane o and the cutter-stand are forced backward as before intimated.
We proceed now to describe the perpendicular part of the cutter stand e f; which is made double, as shewn at i k in [fig. 4] of [Plate 15]; and is also perforated at various heights to receive the bolt which forms the centre of motion of the arm m u, the latter having a cylindrical boss u, fitted into the fork of the stand e f, and so graduated as to determine the angle of it’s obliquity to the horizon, or it’s parallelism to the dotted line w p, which indicates the slope of the bottom of the teeth on the wheel. Finally, the cutter-frame x is fastened to this arm at right angles to it, and thus forms a right angle (or nearly so) with the surface of the wheel: and is, moreover, directed to the centre, produced, of the shaft A B. This latter fact is strictly true, only when the teeth required are of so common a kind as not to require greater exactness: for in theory the sides of the cutter (supposed cylindrical) must alternately direct to that centre—namely, that side which is actually cutting: so that a provision must be made to shift the cutter spindle sideways, a distance equal to it’s diameter; this being no more than what is necessary in every system of wheel cutting.