MAKING CRESCENT
CRANK HANGER.
STAGE 5.
The seat-pillar lug or group, while not altogether seamless, is of the one-piece construction, also having the three lugs drawn and formed upon it. The rear fork jaws are also stamped out of crucible sheet steel, and are of what is known of the semi-hollow construction.
The little brace which is usually placed between the rear forks and back of the crank-hanger and called a bridge, is generally made by a short piece of tubing and brazed to the two rear forks. The makers of the Crescent, who use a D-shaped rear fork, which is drawn to a round shape where it is offset and where it joins the rear lugs on the bottom bracket, make this bridge of two pieces of sheet steel, which are pinned and brazed together and are carried down on each side of the rear forks for several inches in a peculiar lipped shape. It is an expensive method of bridging the rear forks, but greatly adds to the strength at this point and prevents any serious lateral deflection of the frame when the pressure is applied to the cranks on either side. They are the only makers who form their sprockets out of a piece of crucible sheet stamped steel. As it is now made to fit a three-sixteenth chain, which is so popular and which they use, they do not show the wide opening on the flanges of the sprocket between the teeth.
WORKING DRAWING DIAMOND FRAME MODEL. ([See Page 52]).
[Fig. 1] shows the circular steel blank as made by the first operation on a large double action drawing press. It is then drawn into a cup shape as shown in [fig 2]. The practicability of the result obtained is noticeable at once. The edge of the cup is smooth, and there is no wrinkling, cracking or buckling in the steel, and it is still of the same thickness as the original sheet. It is again drawn by successive operations into a cylindrical shape as shown in [fig. 3]. The end is cut off, and the next operations form the lugs as shown in [fig. 4], until the final operation gives the result as in [fig. 5], when the crank-hanger is ready for the joining of the frame tubes. It requires ten days to complete a finished crank-hanger. A marvellous piece of work this certainly is, and it is doubtful if the result obtained in stamping this crank-hanger can ever be equalled by the working of forgings, and the whole result might be summed up by saying that it is “distinctively Crescent.”
BRAZING.
After the drop forgings or stampings are carefully finished by hand or machine, they are carefully cleaned to remove any scale or oil. The tubes having been cut to a proper length, are then closely fitted into the open joint of the forging or stamping connection. In order, however, to hold them securely in place they are pinned through. They are then taken to the brazing furnace. This furnace consists of an open stand, about three feet high, covered with fire brick, pumice stone or coke the purpose of which is to retain the heat. The heat is produced by a mixture of atmospheric air and gas or gasoline, which is controlled by the operator, and supplied by a blower or fan. The flame is applied directly to the joint which is to be brazed by a steel tube, resembling a Bunsen burner, and uses about nine parts of air and one of gas. The combustion or air and gas in the brazing apparatus is about the same mixture as is used in a gas engine. The joint having been brought to the necessary heat, which must in a large measure be left to the judgment and experience of the operator, powdered borax is applied first, the object being to remove any oil or other foreign substance which might interfere with the uniting of the two metals. The borax on being applied flows almost like water. The spelter is then applied, producing a flux, and owing to the expansion of the connection and the tube it readily flows between the joints. The whole operation after the required heat is obtained usually occupies five or six seconds, the object being to secure a joint as rapidly as possible, provided the brazing metal is equally distributed. The gas is then shut off. The supply of air is continued only in order to rapidly cool the joint, the object of this being to prevent the flux from disintegrating and losing its position in the joint. If a brazing has not been rapidly and properly cooled the jar and vibration which the frame receives when in use on a bicycle is apt to cause particles of the flux used in brazing to become loose and rattle in the tube. Necessarily under this operation what might be termed a congregation of scale and the brazing flux is gathered on the outside of the joint. This is afterwards removed by the use of sand blast or pickle, and last, but not least, by hand filing.