Chucking Egg Shells:—The method of doing this so as to enable the turner to cut the shell evenly in two parts, is given by Holtzapffel, in his "Mechanical Manipulation," and has been copied elsewhere. It is ingenious and effective. The object is simply to obtain a pair of delicate vases, to be edged with ivory, and mounted on a pedestal, as a curiosity. The following account is from the pen of the inventor, Mr. G. D. Kittoe, as communicated to Mr. Holtzapffel:—"In the accompanying figure—[Fig. 105]—is represented the nose of a lathe, with an egg chucked ready for cutting." [Fig. 106] is the chuck used first "to prepare the egg, to be mounted in the above way. The latter is generally termed a spring chuck, and is made by rolling stout paper with glue upon a metal or hardwood cylinder, the surface of which has been greased to prevent the paper sticking to it, and upon which it must remain until perfectly dry, when it may be removed and cut or turned in the lathe as occasion may require." [N.B. Nothing is said in the above account of the evident necessity of fixing the paper cylinder to a wooden block, in which a screw must be cut to mount it on the nose of the lathe.] "This sort of chuck is very light—easily made and well adapted for the brittle material it is intended to hold. Before fixing the egg in it, the inner surface should be rubbed with some adhesive substance (common diachylon answers exceedingly well); when this is done the egg should be carefully placed in the chuck, the lathe being slowly kept in motion by one hand whilst with the other the operator must adjust its position until he observes that it runs perfectly true, then, with a sharp pointed tool he must mark the centre and drill a hole sufficiently large for the wire in the chuck, [Fig. 105], to pass freely through. When this is done the egg must be reversed, and the same operation repeated on the opposite end, its contents must then be removed by blowing carefully through it. It is now ready for cutting, for which purpose it must be fixed in the chuck, [Fig. 105]. A is a chuck of box or hard wood having a recess turned in it at a, b, into which is fitted a piece of cork as a soft substance for the egg to rest against. B is a small cup of wood with a piece of cork fitted into it serving the same purpose as that in A. A piece of brass, d, is to be firmly screwed into the chuck A, and into this a steel wire screwed on the outer end, on which a small brass nut e is fitted to work freely in a recess in the piece B. When the egg is threaded on the wire through the holes previously made in it, this nut is to be gradually tightened up until it presses the cup B against the egg sufficiently to hold it steady and firm enough to resist the action of a finely-pointed graver used to cut it. The tool requires to be held very lightly, as a little undue violence would crush the shell. Neither should the latter be pinched unduly tight in the chuck, as otherwise when the point of the tool divides the shell the two parts might spring together, and be destroyed by the pressure. It requires some delicacy of hand to attach the rings to the edges of the shell to constitute the fitting. The foot and top ornaments are fixed by very fine ivory screws, the heads of which are inserted within the shell."
Figs. 105, 106.
Box wood is decidedly the best material for ordinary chucks, as it takes a screw almost as well as brass, is pleasant to work, holds the material firmly, and is of good appearance, which last is not unimportant to those who possess good lathes, and like to see everything in decent order about the workshop, and it is certain that a disorderly workman will commonly produce slovenly work. This wood, however, though tolerably plentiful, is sufficiently costly to be worth preserving, and by a little management chucks may be made to answer for a longer period than might be at first supposed. A chuck, for instance, too large to hold the work, may be plugged with a worn-out chuck of smaller bore, or with wood of inferior character, to save the necessity for hollowing out a new piece of box wood. The latter material, moreover, excellent as it is, may be replaced by other kinds of wood, provided the latter will bear a good screw.
Beech, if dry, will answer very well for the purpose.
Pear is tough and screws well.
Apple is little inferior.
Ilex or evergreen oak is sufficiently hard and tough and will be found quite satisfactory. Elder of large size is good, and screws well.
Sycamore screws well, but is not always equally tough.
All hollow or cup chucks should be furnished with rings of iron or brass to prevent splitting. About six sizes of rings will suffice for a great number of chucks. Bergeron, speaking of the barrel stave chucks already alluded to, prefers the encircling rings plain and not screwed. He gives the following reason:—"If a piece of work entered in such a chuck does not run quite truly, a tap on the ring in the proper place will, by closing the sawgates more in that part, rectify the error, whereas with a screwed ring this is impossible." There is reason in this, but at the same time it would be easy to unscrew the ring a turn or so, give a light tap to the work, test its position by putting the lathe in motion, and when true fix it securely by screwing up the ring. There is, however, one precaution to be taken in making these useful chucks—namely, to cut the staves of equal width, else they will not yield equally to pressure, and the work will not be so readily centred truly. A grip chuck of inexpensive make (one additional pattern of which is introduced from a design by contributors to the English Mechanic) should always be provided. A rough block of ivory for instance may be seized in its jaws, and the exterior useless part cut off by a parting tool as a ring, leaving the nicely rounded material ready for chucking. Ivory nuts or corosos which are peculiarly awkwardly shaped for mounting in the lathe, may also be thus seized, and one portion faced up and rounded so as to allow of being fixed on a face chuck by glue or cement, or fitted into a cup chuck. Rough pieces, too, thus mounted may be faced up, bored and tapped to fit the mandrel as chucks, and a thousand similar works may thus be handled. The simple grip chuck in question is important as having the very useful addition of a centre point which the writer would, if he did not abominate and eschew puns, direct attention to, as the chief "point" of interest—"I call it," says the inventor, a "Universal Self-Centering Grip Chuck." The drawings 1, 2, and 3, almost speak for themselves, to practical turners.