OF
A SCREW,
With greatly diminished Friction.
My readers will perceive, that I have altered the title given in the prospectus to this Invention. It has been done in deference to the opinions of some persons in high reputation in the mechanical world, who hold that there can be no motion whatever without friction. For my own part I am no believer in several sorts of friction: and must therefore, require a new definition of friction, before I can flow with the stream. As the question, however, is not yet before my readers, I shall wave the discussion at present, and describe this invention, as introducing the rolling motion into the threads of a screw; thus taking away the GREATEST PART of the friction on every supposition.
In [Plate 12], [fig. 8], A is the screw, and B C the nut, bored large enough to receive the screw, bodily, without any penetration of their threads. Nevertheless, these threads are made to occupy the same length, in both screw and nut, as though they did enter each other: so that the two parts running parallel to each other, leave a square interstice b, all along both nut and screw: into which balls of brass, or soft iron are introduced, which at once restore the screw-property without it’s friction: a friction so considerable in the common screw, that it always surpasses the effective power, since it remains closed, (in a vice for example) while holding any object squeezed with all the force a man can apply. I have mentioned the use of soft balls: it is in order that they may all act together, and work themselves to a common bearing. It will appear by [fig. 9], that the acting balls might, or perhaps ought to be, separated from each other by a set of smaller ones; since in this case, the surface of the touching balls move the same way, avoiding all friction between them; and leaving the friction only between those surfaces that are exempt from heavy pressure. These circumstances will be understood by consulting the direction of the arrows in [fig. 9]; and I have added two other sketches, to shew the principle in it’s application to square threaded screws, as at [fig. 10]; or to oblong threaded screws, whose threads penetrate each other, in [fig. 12]. I have further, in [fig. 8], sketched one of the methods I propose for supporting the weight of the descending balls, and returning them again into the nut. Considering the balls as a fluid, I have provided a rising column of them, which the working of the screw downward will fill: and the weight of the balls themselves will return them into the nut, when the screw is drawn upward.