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.
Those having quantities of shafts, with a number of shoulders to turn, will recognize in this rest an attachment entirely new in principle and of the greatest importance in the saving of time.
One of the indispensable accessories or attachments, if it may be so called, to an engine lathe, particularly one provided with a long bed, is some kind of a "straightener," by which not only rough bars of stock, but partly finished and finally entirely finished shafts, may be straightened.
The general plan of doing this work is to rest the shaft upon two points at some distance apart and then apply pressure on the opposite side, and at a point midway between these two points.
These attachments or accessories are sometimes attached to the carriage of the lathe; sometimes mounted so as to slide on the V's of the lathe; again upon wheels that run in the space between the inner and outer V's; and in still other cases, for small and comparatively short work, they are mounted upon a bench. In this case they either have attached to them a pair of centers in which the work to be straightened may be placed and its correctness or incorrectness as well as the location and extent of the inaccuracies may be determined, or a pair of V-blocks in which the shaft may be laid while being straightened.
In Fig. 145 is represented one of the latter forms of this accessory made by the Springfield Machine Tool Company, the uses of which will be readily understood by any mechanic. It is intended to be placed upon a bench and to be used when centering work by hand, and for straightening work centered by hand or machine,
Fig. 144.-The Lodge & Shipley Special Roller Follow Rest.
It is a familiar fact that work straightened in a press is more likely to remain straight in the lathe than when hammered straight, and that it is better in every way.
The general arrangement of this machine is in itself very convenient, as any work within its range of centers may be tested and straightened without the unnecessary walking from press to lathe each time in straightening rough or finished work. This, however, does not limit the length of shaft that can be straightened, as any length may be operated upon, thus making it a great labor saver.
Fig. 145. - Shaft Straightener for Bench Use, made by the Springfield Machine Tool Company.
In the tool-room it is especially valuable, not only for centering and straightening work in the rough, but for straightening pieces which have been accidentally sprung in use, or reamers, etc., which have been sprung in tempering.
The blocks upon which the work rests when being straightened are removable to or from the screw and are kept in line by tongues, which fit the groove shown. The shaft is movable through the arm which supports it, being held in any desired position by the set-screw shown, which has a piece of brass over its points to avoid marring the shaft. The centering heads are clamped in any desirable position on the shaft, by the binding screw shown. The top of the arm which supports the shaft forms a pocket for chalk or other material used in marking.
The center at the right is pressed forward by a spring and has a knurled head for drawing it back, both centers being provided with small oil wells. The body of the machine has three lugs cast upon it, by means of which it is bolted to the bench. The block which is on the end of the screw is of cast steel, case hardened, and the centers of tool steel tempered - the whole machine being so designed and constructed as to make it worthy of a place and useful in any tool-room or machine shop where much small work is done. Figure 146 shows the shafting straightener made by the New Haven Manufacturing Company. The base A has cast upon it at the rear a curved standard B, made very strong by proper ribs and extending over to the front. Through the top of this passes a vertical compression screw C, running in a long bronze nut and carrying loosely upon its lower end a V-block D, adapted to fit down upon the round shaft, which is laid into two other loose V-blocks E, E. To insure great rigidity when handling large work the forged stay rod F is provided, its head being held in a T-slot in the base casting and its upper end in a slot cast in the head and in front of the compression screw C, and secured by a heavy nut.
Fig. 146. - Shaft Straightener for use on Lathe Bed, made by the New Haven Manufacturing Company.
At each corner of the base casting is bolted a leg G, G, G, G, carrying loosely journaled therein the shafts H, H, on the outer ends of which are fixed the wheels J, J, J, J, which are adapted to run in the spaces between the inner and outer Vs of the lathe bed, which permits it to be moved to any point where its use may be desired.
In ordinary cases a countershaft is a very simple mechanism. In the older form of engine lathes all that was necessary was a cone pulley identical with the spindle cone, and upon the other end of the shaft a tight and a loose pulley for receiving the driving-belt from the pulley on the main line shaft. Then, as threads required a backward motion of the lathe spindle, a second pair of pulleys was added and a cross-belt applied for that purpose. The shifting of these belts was too slow for practical work and clutches were used. These were of the old "horn clutch" type, making considerable "clatter" in their use and starting the work with too much shock.