Fig. 25.
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].
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.
Fig. 27.
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.