356 



NA TURE 



S^August 1 1, 1887 



the part of the men employed than does that of the portions 

 previously described. 



In conclusion, the author desires to express his indebtedness 

 to Sir John Fowler and Mr. Benjamin Baker, through whose 

 kindness he has been enabled to place before the Institution 

 the foregoing particulars respecting an undertaking which, as 

 shown by the magnitude of the works now being carried 

 on, constitutes one of the greatest engineering feats ever 

 attempted. 



THE MACHINERY EMPLOYED AT THE 

 FORTH BRIDGE WORKS} 



T^HE greater part of the machinery at the Forth Bridge 

 •*■ works is original in design and novel in construction, 

 chiefly because of the unusual nature of the work to be carried 

 out. It may be roughly classed under the following heads : 

 hydraulic bending and setting, planing, drilling, erecting, and 

 riveting. In designing the machinery and tools to accomplish 

 these different kinds of work, there had ever to be kept in view 

 rapidity of production, with a very high quality of work in the 

 finished structure. An idea of the quantity of machinery 

 provided to deal with the material passing through the shops 

 may be partly formed from the fact that it is capable of finishing 

 1500 tons in a single month. 



Hydraulic Bending and Setting Machinery. — To bend and 

 twist the large steel plates required in the construction of the 

 tubes and their connexions, a great variety of hydraulic presses 

 had to be provided. The largest of these is capable of exerting a 

 pressure of 16 X) tons between the dies. It consists of four 24-inch 

 cylinders, resting on two longitudinal girders bedded in concrete. 

 From each cylinder rise two iron colums, which carry a fixed table 

 overhead. On the top of the rams another table is placed, which 

 can be raised or lowered at will. Between these two tables are 

 placed the blocks which stamp the plates to the desired shape. 

 In most cases this shape is the arc of a circle, but in others the 

 form is very varying, while in some instances the plates are 

 flanged as well as bent or twisted. In nearly every case, after a 

 plate has been set while heated, it requires to be finally adjusted 

 when cooled. To dispense with the heating of the plates gives 

 unsatisfactory work, and is in many cases impossible. In no 

 instance is this plan of bending adopted to any extent without 

 annealing the plates both before and after the work has been 

 put upon them. Much of the final adjusting of the plates is 

 done by presses consisting of a simple ram fixed to the upper of 

 two girders, which are bound together at the ends, the lower 

 girder serving as the seat for the block on which the plate is 

 placed. Numerous other forms of presses are employed for 

 lighter work. 



Planing Machinery. — A special class of machinery is em- 

 ployed to plane the edges of the plates. In the case of most of 

 the plates this requires to be done very carefully, because in the 

 structure of the bridge a certain percentage of the stress in 

 compression is taken up by the plates butting, instead of wholly 

 by the rivets as in the tension joints. This statement applies to 

 all plates in the tubes. 



The sides are first of all planed on what may be looked upon 

 as an ordinary planing machine. It is provided however with 

 special double side-cheeks, between which are two fixed swivel- 

 ling tool-boxes, one on each side of the machine. These tool- 

 boxes can when desired be transferred to a special cross-slide, as 

 it is sometimes more convenient to work with one box in the 

 cross-slide rather than with both between the side-cheeks. 

 Both tools act together and cut continuously — that is, during the 

 backward as well as the forward travel of the table. The plate 

 to be cut is fixed upon a curved block, which in turn is securely 

 bolted to the table. 



For planing the ends of the curved plates a special machine 

 had to be designed and built, in which the plates are secured to 

 a fixed table, while the tool is made to travel backwards and 

 forwards in a swinging pendulum that receives its motion 

 through a connecting-rod from a travelling saddle. The tool 

 cuts both ways in this instance also, and is fed to its work by 

 hand. 



The planing machines employed to finish the rectangular 

 plates for girder work are of the usual pattern for plate-edge 



' Paper read by Mr. William Arrol before the Institution of Mechanical 

 Enginee's on Tuesday, August 2. 



planing, but with the addition of an end slide provided with a 

 separate tool for planing one end of the plate at the same time 

 that one of its sides is being similarly treated. This machine 

 finishes a plate at two settings, with the certainty that the ends 

 are at right angles to the sides. 



In some machines two saddles are upon the main slide, and in 

 others two tools are in one saddle ; both devices have their 

 advantages. The facing of the tees, angles, and other sections 

 is done as a rule by cold steel saws, in order to secure good 

 butting. 



Drilling Machinery. — As will be inferred from the varying 

 character of the work, the drilling is performed by various 

 classes of machines. The principle kept in view is that, wherever 

 possible, girders, tubes, &c., should be drilled only while their 

 various parts are temporarily built and held together by bolts in 

 the position they will finally occupy in the finished structure ; in 

 this way the highest class of work is obtained. 



For drilling the tubes, the machines, each complete in itself; 

 are made large enough to embrace the entire circumference of 

 the tube. They consist of a wrought-iron under-frame or 

 carriage, on which are placed the engine and boiler. On it are 

 also fixed two large cast-iron annular rings or headstocks, 

 embracing the tube, round which ten drilling slides and heads 

 travel circumferentially. The slides are moved around the rings 

 and consequently around the tubes by a worm at each end, 

 gearing into a worm-wheel that forms part of the rings. The 

 motion of the drill-heads on the slides is longitudinal, or 

 parallel to the tubes. These two motions easily permit of the 

 ten drills working at any part of the circumference of the tube 

 comprised between the two annular rings, which embrace a 

 length of 8 feet. When this length is finished, the whole machine 

 is travelled forwards, and is again ready to drill a new length of 

 8 feet. The tube rests on timber blocks, which are removed 

 from the front and placed behind as the machine travels forwards. 

 In the case of the lighter tubes, the rale of drilling is as high as 

 12 lineal feet of tube per shift of ten hours; this represents 

 about 800 holes drilled 



The booms of all girders are drilled separately on blocks, 

 thus leaving the bracings to be drilled to template, which is done 

 by radial drills at another time. The machines employed to 

 drill the booms are of a wholly different kind from those used 

 for the tubes. They are moved along rails, running on each side 

 of the blocks upon which the booms are built, and parallel with 

 them. They consist of a double carriage with upright columns, 

 connected together by means of a cross-beain and sundry other 

 framing for carrying the shafts, pulleys, &c. To the columns 

 and cross-beam are secured slides, to which the fixed drill-heads 

 are bolted on the front of the machine ; while to the back are 

 attached radiating arms, each carrying a single drill. In this 

 way there are both fixed and swinging drills on the two sides of 

 the machine, capable of drilling holes in either a horizontal or a 

 vertical plane. The fixed drills serve for all holes in the regular 

 pitch, while the movable drills take what may be called odd 

 holes, such as those where the struts and ties are to be secured 

 to the booms. All the fixed drills are self-feeding, but the 

 movable ones are fed by hand. The number of drills simul- 

 taneously at work varies greatly ; at times as many as thirteen 

 have been employed together on a single boom. 



Other machines having radials with only single drills are 

 used for a special class of drilling, and are found to work to 

 great advantage. With the exception of a few special tools, all 

 the remaining drilling is done by radials capable of making a 

 complete circle round the column on which they are supported. 

 Tables are placed on each side of these machines, and the work 

 is fixed on one of the tables ; and as the drills are placed at a 

 convenient distance from one another, all the drilling required is 

 easily accomplished without a second shifting of the work. 



Erecting and Riveting Machinery. — To erect and rivet such 

 large quantities of material at the immense height at which much 

 of it requires to be done demands a large quantity of special 

 plant for riveting and other purposes. The ordinary class of 

 riveting is accomplished by means of small portable riveters, 

 consisting of two arms held apart by links and stays ; one arm 

 acts as the holder-on, while the other carries the hydraulic 

 cylinder for supplying the power, the cylinder and arm together 

 forming one casting. For some of the more difficult work, 

 where neither could this form of riveter be employed nor could 

 the work be done by hand, small direct-acting hydraulic cylinders 

 were used ; the die for forming the rivet-head was here fixed into 

 the piston. Two 4-inch cylinders were usually employed, held 



