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.
At the front end of the plate there is carried a short-throw cam which allows the plate a slight drop and consequent loosening of the belt when it is desired to shift from one step of the cone to another. The cam rides upon adjustable posts which afford a means of taking up any slight stretch occurring in the belt. The motor back gear shaft is supported at pulley end with an out-board bearing, which prevents any springing of the shaft when the belt is used on the smaller steps of the cone.
The workmanship on the electric motors and their connections, like the work on the lathes and other product of this company, is first-class, and the entire outfit is a good example of mechanical work, although it cannot be said that the design of the device, with its heavy looking bracket supporting the countershaft and motor, is altogether pleasing to the eye. It has rather a top-heavy appearance.
The following illustration, in which Fig. 313 is a front elevation and Fig. 314 an end elevation and partial section, is of an electric drive designed by the author for a 50-inch swing lathe.
Fig. 313. - Front Elevation - Electric Drive for 50-inch Lathe, designed by the Author.
The advantages of having a machine tool, particularly a large one, driven by its own individual electric motor are many, however the electric drive may be arranged. They are greater if the machine was originally designed to be so driven, and particularly with a variable speed motor. But it sometimes happens that we are called upon to arrange an electric drive to a machine already built and perhaps in use in the shop. We may also be required to drive it with a constant speed motor, and must therefore make proper provisions for speed changes.
Under these conditions a large lathe had to be arranged for parties who insisted that the cone pulley in the head-stock should be replaced by a series of gears of varying diameters and so arranged as to engage any one of a second series of gears located on a supplementary shaft in front of them, the gears being placed at unequal intervals, the smallest somewhat greater than the width of their faces from each other. The lathe was so arranged and successfully used, yet the necessary complication of the shifting apparatus, and the difficulty of readily bringing the proper gear into engagement with its fellow by sliding the gear longitudinally, rendered the device somewhat clumsy and inconvenient, and was the cause of some bad language on the part of the man who ran it. The next occasion on which a similar problem arose the customer was not insistent upon any partiular plan, only he "didn't want it like the other one." The motor to be used was of constant speed and the following device was adapted in attaching it to the lathe, as shown by the front elevation in Fig. 313, and the end elevation in Fig. 314.
Fig. 314. - End Elevation of 50-inch Lathe with Electric Drive designed by the Author.
The countershaft cone A is mounted on a shaft journaled in the brackets B, B, attached to the head-stock, as shown. At the rear end of this shaft is fixed a gray-iron gear C. The motor D is supported upon a bracket E attached to the lathe bed and carries on the end of its shaft the steel pinion F. Between the pinion F and the gear C, and journaled on the bracket G attached to the head-stock, is a rawhide gear H engaging both of them. This is introduced to avoid the noise which would otherwise be caused by the fast-running pinion F on the motor shaft. The gear H is constructed with a gray-iron flange on each side, one flange having formed upon it a hub passing through the rawhide blank and the opposite flange, and the whole firmly secured together by six flush-headed screws, the object of this construction being to furnish a good bearing on the stud upon which it runs and also to furnish proper support for the ends of the teeth.
Upon the bosses of the brackets B, B, are formed projecting sleeves upon which are journaled the arms J, J, in the upper ends of which is journaled the belt-tightening roller K, which is composed of a piece of 5-inch extra thick wrought iron pipe, provided with gray-iron heads through which its shaft passes. Through the two end portions of the head-stock, holes are drilled in which is journaled the rock shaft L, upon which are fixed the two levers M, M, the upper ends of which are connected to the arms J, J, by the connecting rods N, N. Upon the front end of the rock-shaft L is fixed the worm segment P, which engages the worm Q, the shaft R of which is journaled in the bracket S fixed to the front of the head-stock, as shown in Fig. 314. Upon the outer end of the shaft R is fixed the crank T for operating the belt-tightening device.
The belt V is cemented instead of being laced, to facilitate its smooth running. By a backward turn of the crank T the belt V is rendered slack enough to be changed from one step of the cone to the other, and a forward turn of the crank tightens it as much as may be necessary to drive the lathe.
In practice it was found that the operator preferred to use the crank for stopping and starting the lathe to examine and caliper his work rather than to use the electric switch or the rheostat, claiming that it was more convenient to allow the motor to continue to run and start the lathe gradually by tightening the belt slowly for that purpose, and we must admit that the operator of a machine, in his daily experience, frequently finds convenient ways to "do things." that the designer or the foreman may entirely overlook.
While the device here shown is simple, and no claim is made of anything strikingly new or original, it has succeeded admirably and given good satisfaction to the proprietors as well as to the employees of the shop where it is in use, and will be found an economical, convenient, and efficient method of applying the electric drive to existing lathes.