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October, 1913 building, and pressed together by hy- draulic cylinders. These strips are 6 in, by 134 in. im section. They are 15/16 in. apart when the pressure is on and 1-1/16 in. apart when it is off, being pulled apart by springs when the pressure released. A» -strip of iron, about 1 in. thick and 12 ft. long, is securely bolted to each forward corner of the carriage, and is adjusted so that it enters without shock the space between the stationary strips, and by its friction against them brings the carriages to rest. Hydraulic pressure is obtained from an electric pressure pump, and an ac- cumulator is fitted, through which the pressure can be varied from 100 Ibs. to 600 Ibs. to the square inch. Gages at the. south end of the basin, one on each side, indicate the pressure in the hydraulic cylinders, enabling the operators of the model to be certain, before-a test, that the friction brake has pressure on. All the strips are kept well lubricated in order to avoid "seizing" or violent shock. is Emergency Brake The apparatus was designed for a maximum pressure of 600 lbs. to the square inch, in order to make ample allowance for all contingencies, and also for uncertainty as to the exact coefficient of friction which would be shown by the apparatus. It is found, however, that a pressure of 300 Ibs. is sufficient to bring the carriage to rest from its maximum speed. As a final provision for safety, there is fitted what is called the emergency brake, which grips the carriage if in any way it gets through the friction brake without being arrested. The emergency brake is a_ longitudinal section of the brake on one side. The Carriage engages a large hook connect- ed by heavy cables and a taper piston tod to a piston working in a_ hy- draulic cylinder. The taper piston tod passes through a round hole ia the cylinder head which it gradually closes as it moves, the principle being identical with the well known hy- draulic recoil brakes for heavy guns. The hydraulic cylinder is below the water level when the basin is full, and when this is the case the emergency brake is always ready, there being no moving parts or adjustments required. Models are, so far as. practicable, made of a standard mean immersed length of 20 ft. The length over all is usually somewhat greater. The model-making apparatus is designed with a view to working originally from the plan of the warship, cruiser or battleship which the model repre- Sents in miniature. Having received Or prepared a correct body plan upon a certain scale, the first step is the determination of sections of a 20-ft. THE MARINE REVIEW model, corresponding to the sections in the warship plan. For this an en- larging pantograph or eidograph is used. It works upon a table covered with a single sheet of thick glass. Having properly adjusted the length of arms by means of the scales pro- THE ELECTRIC MOTOR WHICH HAULS THE MODEL ALONG THE TANK vided, the pointer on the short arm is run around the sections of the body plan, the.pencil on the long arm _ describing the sections desired, upon pieces of paper. These paper sections are used as patterns, from which are 347 This completes the "former model", as it is called. -Its ends are not made to accurately represent the vessel, as it has been found preferable to rough finish only from the former, the ends of the final model and then get them out by hand. Simultaneously with the construc- tion of the former model a wooden block is built up of white pine, about 2 inches thick, glued together hot un- der heavy hydraulic pressure. ~This block is so proportioned that when the finished model is cut from it, the wood will be. left amply thick, no- where less than about 2 inches. Addi- tional thickness is not avoided since the models require ballast in every case. The former model and its corres- ponding block are now secured in the model cutting machine. The roller below rolls over the former model, and the saw above, which is driven at about 2,200 revolutions per minute by an electric motor, is constrained by the balanced link work to move exactly above and at a uniform dis- tance from it. The sizes are so ar- ranged that the saw does not cut within one-eighth of an inch of the intended finished surface of the model. Then the superfluous wood is knocked off and a rotary cutter substituted for the saw, with a corresponding roller. This cutter rough-finishes the model, which is then removed from the ma- chine and finished by hand, the ends, which are left quite rough, being also a) We ) Lan @ @ & & uy HAT ITS SPEED CANNOT BE ISHING THE OUTSIDE OF A MODEL SO TH ae CHECKED BY THE ROUGH SURFACE WHEN BEING TESTED IN THE TANK cut out corresponding wooden sec- tions. Dhey ate clamped im their proper positions upon an iron table, and a skin of strips of wood nailed securely to them and smoothed off. shaped by hand from paper patterns or light wooden templets obtained from the lines. Sanded disks, driven at a high speed by an electric motor, are found to be very efficient and sat-