In the case-hardening department, next door, there are six huge ovens with sliding fronts. Therein are set parts which have been forged or machined, and are subjected to a high temperature while covered in charcoal, so that the skin of the metal may absorb carbon at high temperatures and become extremely tough. All shafts, gears, and other moving parts of a car are subjected to this treatment, which permits a considerable reduction in the weight of metal used, and greatly increases its resistance to wear. After being "carbonised," the material is tempered by immersion in water while of a certain heat, judged by the colour of the hot metal.
We now pass to the turning-shop, where the cylinders are bored out by a grinding disc rapidly rotating on an eccentric shaft, which is gradually advanced through the cylinder as it revolves. The utmost accuracy, to the 1/10,000 part of an inch, is necessary in this operation, since the bore must be perfectly cylindrical, and also of a standard size, so that any standard piston may exactly fit it. After being bored, or rather ground, the walls of the cylinder are highly polished, and the article is ready for testing. The workman entrusted with this task hermetically closes the ends by inserting the cylinder between the plates of an hydraulic press, and pumps in water to a required pressure. If there be the slightest crack, crevice, or hole, the water finds its way through, and the piece is condemned to the rubbish heap.
In the "motor-room" are scores of cylinders, crank-cases, and gears ready for finishing. Here the outside of bored cylinders is touched up by files to remove any marks and rough projections left by the moulds. The crank-cases of aluminium are taken in hand by men who chisel the edges where the two halves fit, chipping off the metal with wonderful skill and precision. The edges are then ground smooth, and after the halves have been accurately fitted, the holes for the bolts connecting them are drilled in a special machine, which presents a drill to each hole in succession.
Having seen the various operations which a cylinder has to go through, we pass into another shop given up to long lines of benches where various motor parts are being completed. Each piece, however small, is treated as of the utmost importance, since the failure of even a tiny pin may bring the largest car to a standstill. We see a man testing pump discs against a standard template to prove their absolute accuracy. Close by, another man is finishing a fly-wheel, chipping off specks of metal to make the balance true. We now understand that machine tools cannot utterly displace the human hand and eye. The fitters, with touches of the file, remove matter in such minute quantities that its removal might seem of no consequence. But "matter in the wrong place" is the cause of many breakdowns.