MAKING DROP FORGINGS.
A drop-forging differs from a hand-made forging because it is made from a bar of steel suitable for the purpose required and formed in dies placed in drop hammers, this bar of steel having been previously heated to the proper degree in a furnace adjacent to the drop hammer which is used. A drop hammer may be described as follows: The main part of the machine consists of a heavy anvil, or base, weighing from 7,000 to 30,000 pounds, depending on the size of the hammer. To this is attached two vertical uprights, between which the head or ram of the hammer works. On the top of these uprights is the lifting mechanism, a board being attached to the hammer and the rolls that revolve in the head act upon this board and lift the weight by friction. In the base first mentioned are fastened the lower dies, the upper die being attached to the hammer. In these dies the impression for the forging wanted is cut by skilled mechanics, the dies afterward being tempered to make them as hard and durable as possible. The piece of steel having already been heated to a white heat, is held on the lower die by the workman, who then operates the drop hammer by means of a foot treadle, the hammer with the upper die dropping by gravity and forcing the heated metal into the impressions cut in the dies.
THE STEARNS.
The surplus metal which has protruded between the lower and upper dies resembles a fin or web; this has caused the forging to be mistaken for a casting of iron, because the fin resembles in no small degree the gate or connection between castings when moulded. This fin of metal is trimmed off from the forging by means of another machine, called the trimming press, to which are fitted dies for this purpose. Experts in the trade say that no “hand-made” forgings or “castings” can ever wholly take the place of drop forgings in bicycle construction. Drop-forging manufacturers say that hand-made forgings are obsolete, owing to the enormous cost of manufacture.
WOLFF-AMERICAN
LAPPED JOINT.
Malleable iron castings, or steel castings, are used by some of the makers, but entirely sub rosa. They are apt to be full of blow holes and other defects and not at all reliable, and the maker of high-grade bicycles who advertises that he uses such castings in his bicycles will soon find himself out of the market with his product entirely on his hands.