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.
Later on friction clutches or friction pulleys were devised, and these in one form or another are largely in use at the present time.
Up to a comparatively recent date the lathe had but two speeds, so far as the countershaft controlled it. One was the usual forward speed, the other a considerably faster speed backwards, mostly used in thread cutting. Occasionally, for special work, this "backing" speed was taken advantage of by changing the cross-belt for an "open belt," and thus getting another range of speeds. Doubtless this suggested the advantages of a regular two-speed countershaft which has now become quite common, as a convenient and economical method of adding another series of speeds to the lathe.
There are now used on a number of popular lathes geared countershafts as well as various devices for producing a variable speed by a gradual increase or decrease of the number of revolutions per minute. This result has been sought by a number of different devices with more or less success. Some of them have had good features to commend them while others were more in the line of makeshifts that accomplished the results sought very inefficiently and partook too much of the nature of "traps" as understood by the machinist, and hence were comparatively short-lived and unpopular.
Figure 147 shows a good example of the regular type of lathe countershafts. It is made by the F. E. Reed Company, and consists of the cone pulley, a counterpart of the spindle cone part, and two friction pulleys mounted upon the shaft, which is supported in two hangers having self-oiling boxes. The friction pulleys consist of the pulley proper A, which is turned on the inside of the rim for the reception of the friction band B, or has cast with it a rim projecting from the pulley arms and finished inside for the same purpose, as shown in the engraving. The friction band B is divided at one point as shown, the two loose ends having projecting lugs at b, b, drilled for pivot bolts by which it is connected with the levers C, C, whose ends are adjustably connected by the screw and nuts shown at d.
Friction Pulley, complete,
Friction Ring, or Clutch.
Fig. 147. - Friction Countershaft for Engine Lathes, made by the F. E. Reed Company.
Sliding upon the shaft between the pulleys is the clutch collar E, whose horns e, e, are adapted to enter between the ends of the levers C, at /. These horns being wedge-shaped will, when thrust between the free ends of the levers C, C, spread them apart, and as their fulcrum ends are connected, and by means of the pivot bolts connected to the free ends of the friction band B, tend to extend the opening of this band, enlarge its diameter, bring it in contact with the inner surface of the pulley (or of the rim cast upon it for that purpose), and cause sufficient friction to transmit the required power.
The clutch collar or sleeve E is provided with a square groove at its center to accommodate the shipper fork, by means of which it is moved to and fro on the shaft, according as one or the other clutch is to be thrown into an active position and the lathe to be driven by the belt on the one or the other pulley. One of the pulleys carries an open belt and the other a cross belt.
There are various forms of friction pulleys and friction clutches used on countershafts, but all are designed with analogous parts to the above and perform similar functions. Therefore there is no need for a detailed description and illustration of them. In all of them the pulleys run loose on the shaft, except when clamped to it by means of the friction device, the disc or friction band B, or its equivalent, being fixed to the shaft.
In the center of the shaft between the pulleys is usually a sliding sleeve that operates the friction mechanism, as here shown, and by which it is connected to the shipper lever within easy reach of the operator.
The tight and loose pulleys are still used on very heavy lathes, and in this case, when both the forward and backward motion is desired, there is one tight pulley a little greater in width than the belt, and on each side of it a loose pulley of double this width. The belts are so located that each is on one of the loose pulleys when the shipper handle is in its middle position. When it is moved to the right of this position the left belt is moved on to the tight pulley and the right belt travels to the right on its loose pulley. By moving the shipper handle to the left the reverse effect is produced, and the right-hand belt becomes operative. The pulley on the line shaft is, of course, as wide as all three on the countershaft.
Fig. 148. - Self-Oiling Boxes for Countershafts, made by the F. E. Reed Company.
In Fig. 148 is given a good illustration of the self-oiling countershaft box, which is used on the countershaft shown in Fig. 146.
As will be seen by the engraving (Fig. 147), the journal box A has formed beneath it an oil reservior B for holding a quantity of oil sufficient to last several weeks. Near each end is a groove containing a wick or strip of felt C, C, surrounding the shaft and reaching down into the oil reservoir B, by means of which an ample supply of oil is always delivered to the journal bearing. The wick may be introduced and oil supplied by opening the hinged covers D, D.