The annexed engravings are a front view I (figure 1) and a side section (figure 2) of a very simple and ingenious variable eccentric, by C. A. Holm, a London mechanic, and published irom drawings in the London Artisan: It is designed for the throw ot a crank or eccentric where there is not room for the ordinary slotted crank, a is the shaft from which the motion is communicated, on this, shaft is keyed the eccentric disc, b. In the centre of this disc is a stud, c, which is screwed into the centre of another disc, d d. This latter disc has a pin, c, fixed in it, eccentric, from sing the shaft, a, to revolve, it is clear that the stroke given to the pin, e, will be double the iadiu#bm centre 6F a to centre of e. But, if the screw, be slackened, the disc, d d, can V turned round until the centre of c is brought over the centre of a, when e will have no motion at all. And any point between these two will give a different stroke, as ? shown by the dotted lines in figure 1. Lines are engraved on theedge of the disc as 1, 2, 3/4, 5,6, and 7, which give the different ranges of stroke. Every engineer and person acquainted with a steam engine will at once perceive that this is a very simple device for setting the throw of an eccentric and crank. Its value will at once be appreciated by the fraternity. It is a on any engine, and it is equally applicable to various forms of expansion gear as well as the eccentrics of steam engines.
This article was originally published with the title "Variable Eccentric" in Scientific American 8, 8, 64 (November 1852)