Chucking work in the lathe is one of the most interesting branches, for here there are no centers in the way, to plague the workman, and the tool has a fair sweep at all parts. Every one who uses a lathe, should get a scroll chuck, Fig. 21, of Cushman’s make, (A. Cushman, Hartford, Connecticut,) that is, a chuck where the jaws move up together toward the center, so that any round piece will be held perfectly true. This is a great convenience, for whether we have a ring to bore out, or a wheel to turn off, it is equally handy, and is far better than the independent jaw chuck, which has to be set up by measurement, and repeated trials before it is right. To those who cannot afford to purchase a scroll chuck, a wooden one can be made to answer every purpose. Wooden chucks should be made of some hard, fine-grained wood, such as maple or mahogany, so that they will hold well whatever is driven into them.
If we have a small cylinder head to turn, for instance, the back head, which has no hole in it to put a mandrel through, as the front one has, the wooden chuck will come in play. To make one, the turner takes a square block of the proper thickness, say one inch, and saws the corners off, so that it is eight-sided. It is then ready to screw on the face plate of the lathe. This is quickly done by having small screw holes in the plate for this purpose, as shown in Fig. 1, page 17.
The block is then all ready to work on, and the face must be turned off true, and a recess cut out in it to receive the head. This is the head, Fig. 26.
On the back side, there is a projection to fit the cylinder of the engine. This must be turned first, and the flange faced off true: after that the head must be pryed out, (by making a little recess in the chuck, alongside of it,) reversed, and put in the chuck again, the finished side in, so as to polish it on the outside. Fig. 27. It must be driven up tight against the face of the chuck, otherwise the flange will be thicker on one side than the other. In finishing, it will be found better to commence near the center, and work out toward the largest diameter, for it is necessary to get under the scale, or sand, left on in casting, first, before the work can be turned true, and this is easiest done by beginning at the middle, where the speed is low. The scale is fused sand melted on the metal in the act of casting. The best tool to do this with is the diamond-point, for it can be employed universally on straight or hollow surfaces, is easily ground, and always works well. After it, comes the scraper, previously shown. If these chatter, a piece of leather must be put between them and the rest. It is also well to put a stout iron rod, or piece of hard wood, between the back center of the lathe and the face of the plate; this keeps everything steady, as shown below, so that a beautiful luster will be given by the tool alone.
After the plate or head is firmly scraped, it must be polished with flour emery and oil. The emery first used must be No. 1, which is about like Indian meal; if the work is brass, however, this will not be needed. This must be plentifully supplied with oil, so that it is like cream, and the workman, taking a soft pine stick, with the end pounded into a brush, so that it will hold emery, holds it hard up against the face of the head. If it has been properly scraped, a few revolutions will produce a fine-grained finish, but if it is badly done, the corners will be full of scratches and chatters. It takes time and experience to make a good finisher, and patience also, for men who are good turners, and can make excellent fits, are sometimes botches at polishing.
After emery of the finest possible description has been used, a little rouge powder should be put on a piece of buckskin and applied to the work. This will make a polish equal to gold on brass, and like silver on iron. Instead of these methods many persons burnish their work. The burnisher is sometimes made of steel, of bloodstone, and of agate. Steel is the material generally employed. It is polished as bright as can be on a buff wheel, and must be preserved so, otherwise it is useless to attempt doing anything with it. Pumice stone is very good for polishing with, or rather for finishing the surface before polishing. Other substances will be mentioned hereafter. Steel and iron are best polished with a sharp tool and water. To turn steel with a handsome surface, the tool must be sharpened on an oil stone, and the speed high, then spit on the work and take light cuts, and you will have a nice job. To make a very brilliant polish on steel, it is necessary to use emery and oil, plenty of oil and not much emery, but this makes such a nasty mess on the lathe, that few good turners will do it. A file should not be used in the lathe if possible; filing a job makes it uneven, and spoils the looks of it. It is difficult to avoid scratches, and the expert can generally tell the difference between work that has been turned true, and that which has been filed, and, in nearly all cases, it is quicker to turn the work to fit or to finish at once.
In polishing round work, such as rods or shafts, it is much cleaner, and more expeditious, to make a pair of clamps like Fig. 28, and put the emery and oil on leather pads between them. The clamps consist of two straight pieces of soft or hard wood, lined with leather, though some use sheet lead.
The leather catches the polishing material and holds it, and, at the same time, keeps it continually applied to the shaft. The clamps are slipped over the same, and the ends held in the hand. This utensil also gives a fine finish to the work, making it smooth and even. It must be carried regularly along from end to end, sometimes fast and sometimes slow, so as to cross the lines, or avoid making a twist in the polish like a screw thread, which would otherwise be given. A very beautiful and brilliant luster can be given to a shaft of iron or steel, after it is nicely finished, by holding a sheet of fine sand paper, covered with chalk, on it. The glaze that this gives, makes the work glisten like silver, but it also takes off all the grease, so that the shaft is very sensitive to moisture, and is quickly rusted.
This discussion about polishing has led us away from the consideration of chucking, which we shall enlarge a little more upon.
The chuck is a very necessary and even indispensable auxiliary when chasing. Threads cannot be caught in the jaws of a scroll chuck, because, if set tight enough to hold the work, the threads are jammed so that they will not run in the part they were fitted to. If a piece, having a thread cut on it, like Fig. 29, is to be turned outside, it is very easy to chase the cap first and then the cup it fits, so that the cap can be screwed into it and turned off where it belongs; it will then be true, and is easy to mill on the edge.
It must always be borne in mind that the chaser must be sharp. If it is not, drunken threads will be the rule, not the exception.
The chuck shown in Fig. 30, will be found very useful for holding metallic disks, small box covers, or anything that requires merely a slight clasp; it is also useful for holding round plugs, pencils of wood, or penholders, to drill in the ends. It can be made eccentric with the mandrel of the lathe, if desired, so as to turn a piece on one side, or drill in a similar manner in the end of a plug. It is merely a piece of boxwood bored out, bored with holes, which are sawed down into slots, so as to form a series of jaws, which are sprung in by sliding the ring down on them. They are so easily made that a great many can be provided.
