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.
System of electric drives. Principal advantages of driving lathes by electricity. Group drive versus individual motor system. Individual motor drives preferable for medium and large sized lathes. The Reed 16-inch swing motor-driven lathe. The Lodge & Shipley 24-inch swing motor-driven lathe. The Prentice Brothers Company's motor-driven lathes. General description. Crocker-Wheeler motors. Renold silent chain. The Hendey-Norton lathe with elevated electric motor drive. Special features. A 50-inch swing lathe with electric motor drive designed by the Author. Detailed description Practical usefulness. Not strikingly original, but successful.
One of the more important developments of the modern machine shop tools is the electric drive, with which many of them are equipped. While the system of driving by electric motors has many phases, and all of them most interesting problems, this chapter will be more particularly concerned with the question of individual motors for the machines, leaving out the question of driving a group of machines from a "jack shaft" operated by a single motor, and the plan of driving line shafts in the same manner.
There are many advantages in driving machines, particularly lathes, with individual motors; among them being:
First, the power, and in case of variable speed motors the speed is directly under the control of the operator;
Second, there is economy in the use of power, as none is used to drive "jack shafts" or countershafts;
Third, there is also economy in the use of power as none is consumed except when the lathe is in actual operation; and Fourth, the wear and tear of belting is either reduced to a minimum or eliminated altogether.
While it may be still an open question whether the "group drive" system or the individual motor system is the better, particularly for small lathes, there seems to be no doubt of the individual motor system for medium and large lathes, say from 24-inch swing upwards.
In this chapter, therefore, it is proposed to describe and illustrate the modern individual motor system as applied to lathes made by the American up-to-date builder of lathes, and in doing this to show those put on the market by the more representative concerns engaged in this business.
Fig. 308. - 16-inch Swing Reed Motor-Driven Lathe.
In Fig. 308 is shown a 16-inch swing Reed motor-driven lathe. The motor is one-horse power, direct connected, with variable speed. The motor and its controller are built by the General Electric Company. The motor has a speed of from 500 to 1500 revolutions per minute.
As shown in the engraving the motor is geared directly to the main spindle by suitable gearing so that no belt is required. This method seems preferable to the plan of using a short belt. The noise of fast running gears, in a device of this kind, may be avoided by introducing a rawhide intermediate gear next to the small steel pinion on the motor shaft, by which means the gears will run comparatively quiet even at a very high rate of speed of the motor shaft.
The Lodge & Shipley 24-inch swing motor-driven engine lathe is shown in Fig. 309. This design uses a short belt in driving from a small two-step cone on the motor shaft to the spindle cone. The motor is of the variable speed type with a speed variation of two to one.
Fig. 309. - 24-inch Swing Lodge & Shipley Motor-Driven Lathe.
The motor is mounted on an overhead bracket directly above the head-stock, pivoted at the rear to two heavy standards bolted on to the back of the bed, and is connected to the driving pulley by a short, wide belt, in which sufficient tension for driving is obtained by means of the adjusting screw with a hand wheel at the front of the head-stock.
When this system is used the cone pulley has two steps, and two sets of back gears are provided, so that the combination affords a total of six speed changes, two with the lathe out of gear and two with each of the back gears in. By varying the speed of the motor, either through the introduction of field resistance or by use of one of the multiple voltage systems, intermediate speeds in each range are obtained, the number of which depends only on the number of points in the controller. With a 20-point controller, 120 distinct spindle speeds are thus afforded.
This company also equip their lathes with constant speed motors, for which purpose they mount the motor at the rear of the head-stock near the floor. From a small pulley on the motor shaft a belt runs up to a large pulley on a countershaft located directly in the rear of the head-stock. This countershaft carries the usual speed cone, from which a short belt connects with the spindle cone in the usual manner. The countershaft speed is from 125 to 200 revolutions per minute.
In buying a motor-driven lathe, the purchaser has usually to decide between a direct-connected and a belt-connected lathe, and between a constant speed and a variable speed motor. The use of a constant speed motor direct geared to the lathe is practically prohibited, on account of the mass of gearing necessary to secure sufficient speed changes.
This may be obviated by using the countershaft as above arranged, although it is well known that short belts are objectionable on account of the high tension that must be maintained to render them capable of transmitting the required power to properly operate the lathe.
The Prentice Brothers Company equip their 14, 16, 18, 20, and 22-inch swing engine lathes with a motor drive device which is shown in Fig 310.
In this case the motor is under the bed and close to the head cabinet. Eight changes of spindle speed are provided for by means of a series of gearing located in the head-stock of the lathe. All of these speeds are available without stopping the lathe. The gearing is so arranged that it is impossible for the operator to interlock any conflicting ratios of gearing. This is an advantage that is greatly appreciated, as it removes all possible danger of breakage to the gearing or the clutches in the driving mechanism of the machine.