(9) °The Machine Shop° is equipped with an endless variety of metal working machines such as planers, boring and turning machines, etc., which are employed to finish the bearing surfaces of the riveted members and other parts which are used in their construction, such as pins, rollers, beds and sole plates, anchor bolts and the yarious bearing parts of turntables.
The material for the pins and rollers as usually received from the mills has a diameter 1/2 inch greater than that of the finished pins, and has to be turned down to the required size, and the threads cut on the ends for the pin nuts. The planers are employed to smooth off the faces of the bed and sole plates of the ex pansion joints.
(10) °The Forge is equipped to turn out three classes of work — the manufacture of rivets, the general smith-work required in a steel structure and the forging of eye-bars.
The soft-steel bars of which the rivets are made are first heated and then passed into the rivet-making machine where they are upset, headed and cut into the required lengths at one operation. The rivets most generally ein ployed in structural work range from 34 to h inch in diameter.
The operations designated as general smith work consist of the bending of plates, shapes and angles in accordance with the requirements of the drawings, the upsetting of the ends of adjustable tension members, the making, of devices and loop eye-rods, and all forgings such as punches, drift-pins and riveting cups that may be needed by the plant.
All the large tension members of pin-con nected structures are made in this shop. The steel flats from which these eye-bars are made are handled as follows: About four feet of one end of the bar is heated to a cherry red in the forge and then placed in the upsetting machine which forms a solid head very nearly the size of the finished head. It is then reheated and placed in the die of the steam hammer and hammered out to the proper size and thickness, and a hole punched in the centre of the head to facilitate the finish boring. A careful watch is kept for flaws, and all of those discovered are cut out since they prevent a perfect weld, and are, no matter how small, a source of weakness in the bar. The head on the other end of the bar is formed in a similar manner. A number of bars are then placed in the annealing furnace and brought gradually to a cherry red temper ature, after which they are allowed to cool gradually so as to remove local stresses that might have been induced by the processes em ployed in upsetting and forging the head. The exactitude required in this work is indicated by Cooper's Specifications, 1901, according to which, chord pins are required to fit the pin holes within 16o of an inch for pins less than 41/2 inches diameter; while for larger pins, the clearance may be 'An of an inch. It is also re quired that the bars must be bored to lengths within Um of an inch for each 25 feet of the total length.
(11) The Painting and Shipping Depart ment>> consists of sheds and yards where the material, after being inspected and stamped, is painted and prepared for shipment.
The facility with which bridge work is carried out depends very much on the character of the drawings supplied. Bridge designers cannot be familiar with the preferred practice in all shops, as these differ; they cannot cer tainly know what concern is to do the work. It
is therefore best not to attempt the smaller details for the first set of designs, and after the work is awarded to a shop allow them to make their own shop drawings in duplicate, adapting them to their own equipment and methods. This is an economy. Those respon sible for a bridge, however, require to be care ful that the builder does not cheapen construc tion at the cost of strength. There is a con tinual temptation to do this, as seen in the lamentable fall of the Quebec Bridge in 1907, where a badly weakened beam passed inspection, and precipitated the fall of the entire structure. Shop designers will know enough to position rivets so as to permit of gang punching. They will avoid beveled cuts and hand riveting, which add to cost; and they will not mark holes for reaming where the strength does not require it. They will avoid the use of side plates, which are always a nuisance; when work is to be left for field riveting they will look out that the rivets may be driven from the top; and in the case of box-shaped columns or the like they will position the angles or channels outward so they may be power-riveted. They will bear in mind that a solid web is stronger, simpler and cheaper than close lacing. Such drop drawings should be carefully marked with all necessary informa tion, as size of rivet holes both before and after reaming, the manner of finishing the edge of webs, etc.
After leaving the shops, and before ship ment, the material is carefully examined in de tail to see that it conforms in every particular to the drawings and specifications, by the in spectors of both the bridge company and the purchaser. A large percentage of this work is done by inspection companies. These companies employ a large number of inspectors who are sent from one place to another to examine the work on hand. The inspection companies bid for the inspection work at so much per ton of material. Although these companies usually keep a permanent inspector at the works of a large bridge concern, and are therefore able to greatly reduce the cost of inspection to the pur chaser, the system is subject to many objections, the principal one being the fact that the actual inspector is personally unknown to the pur chaser. The exceedingly satisfactory services rendered by these companies, however are clearly demonstrated by the large amount of work handled by them, and their high profes sional reputation.
The general method of inspection may be briefly stated as follows : When the inspector of the purchaser arrives at the works of the bridge company, he is furnished with a set of the plans and drawings of the bridges to be inspected, and starts in at once to familiarize himself with the shops and working methods of that particular plant. He then ascertains the rolling mills from which the rough material for the structures will be obtained, and begins the work of actual inspection at that point. All the material is carefully examined for flaws and surface defects, and tested for strength, and when found satisfactory is stamped by him with a hammer, and then forwarded to the works of the bridge company. Subsequently, he keeps a general oversight of .the material as it passes through the various shops and departments of the bridge works until it has passed out of them and is ready for the final examination.