This section is from the book "Lathe Design, Construction And Operation, With Practical Examples Of The Lathe Work", by Oscar E. Perrigo. Also available from Amazon: Lathe Design: Construction And Operation.
As the supply of oil is so profuse there is the liability of waste by its running out at the ends of the journals. This is prevented by providing the return oil grooves E, E, at the ends, which conduct the oil back to the oil reservoir. The design and arrangement is very simple and at the same time very effective. It is used with slight modifications for many similar purposes with like success.
Fig. 149. - Reeve's Variable Speed Countershalft.
In Fig. 149 is shown the Reeves' variable speed countershaft, which has proven a valuable device when the speeds required are not excessive. It is well adapted to nearly all machine-shop tools and by its use a great range of speeds may be obtained.
It consists of two shafts B and C, journaled in the frame A, in the usual manner. Upon the shaft B is splined the rather flat cones D, D, and similarly connected to the shaft C are the cones E, E. These cones are adapted to slide freely to or from each other on their respective shafts, and their movement is governed by the levers F, F, which are fulcrumed at f, f, and pivotally attached to the hubs of the cones D, D, E, E, by suitable collars. The farther ends of these levers are pivotally connected to a screw G, by suitable nuts running on right and left threads, whereby the nuts may be drawn together or forced apart as may be necessary, carrying with them the ends of the levers F, F, and consequently the cone discs D, D, E, E, but by an opposite movement; that is, as the discs D, D, approach each other the discs E, E, recede from each other. Upon the end of the screw G is the sprocket-wheel H, from which a chain runs to another sprocket-wheel near the operator, who may handle it by means of a crank upon the shaft of the latter wheel.
Running within the cone discs D, D, at one end, and E, E, at the other, is a series of wooden lags connected by a chain mechanism by which it becomes in effect a belt, the ends of the lags bearing against the inner, inclined surfaces of the cone discs.
The length of the wooden lags being constant, it follows that as the cone discs are forced closer together the lags will ride up on a larger diameter, and simultaneously the cone discs on the opposite shaft will, by the mechanism described, be drawn farther apart, permitting the lags to run closer to the shaft and on a correspondingly smaller diameter.
Now, as one of the shafts B, C, is driven by a belt from a pulley upon the main line shaft, while the other carries the pulley (in this case a cone pulley) driving the machine, the speed of the same may be varied at will, as one pair of cone discs are forced nearer together and the other pair farther apart, thus, in effect, changing their relative diameters and consequently their speeds.
Geared countershafts are also used upon lathes for producing variable speeds. They depend, of course, upon the usual methods of ,bringing into active operation pairs of gears of varying diameters by means of clutches, sliding gears, and similar devices. The noise of the gears is one great objection to their use. This has been partially avoided, or smothered, by enclosing them with a casing, which partially obviates another objection, that of throwing oil and dirt upon the floor, the machines, and the workmen.
Another form of variable-speed countershaft was brought into use some years ago which consisted of two comparatively long cones placed side by side but in reverse positions so that their adjacent sides were parallel. They were mounted upon parallel shafts, one being the driven and the other the driver. Motion was transmitted from one to the other by means of a short endless belt running between the surfaces, with the slack end hanging below them. This belt was controlled by a sliding belt guide by means of which it could be moved from end to end of the cones, whose varying diameters at the point of contact determined the speed transmitted from one shaft to the other.
While this device was entirely operative and, with light loads, reasonably successful, it was not well adapted to transmitting any considerable amount of power, owing to the very small area of contact surface between the cones and the belt, the pressure upon which had to be excessive in order to transmit the power required even for light work.
Unusually large cones would no doubt have added materially to its transmitting power, but as a practical mechanism it was not the success that its admirers hoped it would be.