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.
For the purposes of this work it will be sufficient to present a few of the more recent examples in this chapter and to call attention to the engravings of a number of others in other chapters wherein the lathes of prominent builders are illustrated and the change gear devices shown. Among these are the lathes built by Hamilton Machine Tool Company, Bradford Machine Tool Company, Hendey Machine Tool Company, Prentice Brothers Company, Springfield Machine Company, etc.
Fig. 171. - End Elevation of Le Blond's Quick Change Gear Device.
The quick change gear device designed by R. K. Le Blond is an interesting example of this type of mechanism. Figure 171 shows an end elevation of this lathe, and Figs. 172, 173, and 174 some of the details of the gearing.
The lathe, with the exception of these features, is the same as the standard engine lathe built by this company, and the head-stock end is shown in Fig. 171, which gives a good idea of the exterior appearance of the change gear device.
The line drawing, Fig. 172, shows the connection between the feed box and the lathe spindle. The spindle gear A drives gear D on the stud DD through tumbler gears B and C. The tumbler gears are of the regular construction used for reversing the motion of the carriage in screw cutting, so as to cut either right or left hand threads, as required.
Motion is transmitted from the tumbler gears through gears D, Ed G, and H, which latter is on the driving-shaft of the feed box. In order, however, to obtain a second series of feeds there is a telescopic slip gear located on the stud D1 which can be made to mesh with gear G in place of pinion E1 which is shown in mesh with gear G in the engraving. To accomplish this, G rotates on a pin in a quadrant G1 which, by means of the clamping handle G4 and the stops G2 and G3 can be brought into the correct position for gear G to mesh either with pinion E1 or gear F, as required. The hub of gear F is recessed so that it can be slid over pinion E1, thus bringing this gear in the same plane with gear G. Gears D and F and the pinion E1 all rotate with the stud, which is journaled in a bearing in the head-stock casting. The introduction of the telescopic gear F makes a change in the feed ratio of 4 to 1.
Figure 173 is reproduced from the patent specification and shows clearly the mechanism of the feed box. A is the driving shaft and B the driven shaft, which in this case is represented as being one end of the lead screw, but in the actual lathe is connected with the latter by suitable intermediate gearing. However, the principle of the feed changes is the same in either case. Shaft B carries a cone of gears and shaft A an elongated spur gear C, which is the driving gear of the mechanism.
Surrounding this elongated gear C is a cylindrical barrel D, which serves the double purpose of a casing for the gear and a bearing for a sliding bushing E, by means of which the adjustment of feed is effected. This bushing carries at F an intermediate gear which at all times is in mesh with gear C and can also be brought into mesh with one of the gears in the cone by giving the bushing E a combined sliding and rotary motion on the barrel D.
Fig. 1,72. - Sectional View of Le Blond's Quick Change Gear Device.
The portion of the barrel D which is toward the cone of gears is provided with a longitudinal slot, to allow the intermediate gear F to project through and mesh with gear C. The front portion of the barrel is provided with a series of holes, corresponding in number and position to the gears of the cone, so that the bushing which carries the intermediate gear F can be locked in its proper position for each gear by means of a spring pin, after the usual manner. The bushing which acts as carrier for the gear, and the barrel which encases the elongated gear, are clearly represented in the detailed view of the mechanism, Fig. 173.
Fig. 173. - Details of Le Blond's Quick Change Gear Device.
Figure 174 is a view looking at rear of the mechanism and its casing, and shows the modifications that have been made in the device to adapt it to the engine lathe. The cone shaft carries besides the eight gears of the cone, an additional gear, K, and below this shaft, which is marked B, is the shaft L, which is connected directly to the feed rod R, and carries a sliding sleeve S, on which are two pinions, M and N.
In the position shown in this view power is transmitted from the cone shaft B to the gear N by means of the auxiliary pinion K, and as the sleeve S is splined to shaft L the motion is transmitted to this shaft and thence to the feed rod. By sliding the sleeve to the right, gear N no longer meshes with pinion K, but instead pinion M meshes with one of the gears of the cone, causing the feed rod to rotate at a faster speed. The lead screw T is driven from the feed rod by a slip gear W, in the usual manner.
From the above description it will be seen that with the gear box itself eight changes of feed are obtained. The slip gear on the auxiliary shaft in the feed box makes 16 changes, and these 16 changes are again doubled by the telescopic gear on stud D1 in Fig. 2, making 32 changes and giving a range of threads from 3 to 46 per inch, covering every standard thread, including 11 1/2.
Fig. 174 -. Rear View of Le Blond's Quick Change Gear Device.