Page:The Kinematics of Machinery.djvu/377

 DAWES, TCHEBISGHEFF. 355

80.

Chamber-crank Trains from the Isosceles Turning Slider-crank.

(Plate XVI. Fig. 1.)

The special case of the turning slider-crank which occurs when the lengths of the coupler and crank are made equal has been riot unfrequently employed in chamber-crank trains. PL XVI. Fig. 1, shows a steam-engine formed from it by Dawes* in 1816. We called the mechanism the isosceles turning slider-crank. Here again the frame or slide d is made the fixed link, so that its general formula is (CJ ^C"'P- L ) d . The piston is part of c and the chamber of d, so that we have also V c, d. The special formula is there- fore (C"^C"P- L )c. The coupler is prolonged and carries on its further end a second block c v moving in a slide d v which forms one piece with d. The chain is thus closed by the addition of a second chain, equal and similar to the first but placed at right angles to it, instead of by the pair-closure described in 47 and 70.

The object of this mechanism is to reduce the distance between the crank-shaft and the cylinder; an examination of it shows, however, that it possesses such constructive difficulties as to leave it little practical value. It appears, however, here and there, as for instance at the London Exhibition of 185 1,*!* and in 1868 at the Exhibition at St. Petersburg. At the latter place Prof. Tchebischeff exhibited a working model, in which the second prismatic guide was replaced by an augmentation of the chain ( 67) in the shape of a "parallel motion" designed by him.J


 * Severin's A bhandlungcn (Mittheil. des techn. Dep. far Gewerbe 1826), p. 64.

t See Booth's Machine in the Official Catalogue^ vol. i., p. 219.

Berliner Verhandlungen, 1870, p. 182. The Imperial Technical School at Moscow exhibited at Vienna, in 1873, a sectional model of this arrangement which was illustrated in Engineering, vol. xvi., p. 284.

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