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.
An expert blacksmith forged a twist drill 2 inches in diameter with a twist of 31 inches in length, which was turned up and finished, and with this a hole was bored a little over 30 inches deep. A soft brass tube of about 2/10-inch bore, carried oil under pressure to the point of the drill and on its return brought out the chips. The spindle was then reversed and the hole was bored from the opposite end until the two holes met, which they did quite exactly.
Now came the work of enlarging the hole from 2 inches to 5 1/8 inches. It is to this part of the work that particular attention is called. As the means for holding the drill had proven very rigid and satisfactory, a boring bar was constructed, as shown in the upper illustration, Fig. 222. The cutters a and b were of 3/4-inch round steel, fitted in the usual way, and held by set-screws c, the bar being placed in a lathe and its ends turned off, so that the cutter a would measure 3 7/8 inches, and b 5 1/8 inches. The end of the bar just fitted the 2-inch hole already bored in the spindle, thereby furnishing a correct and certain guide and support near the cutters. The cutting ends of the cutters were formed as shown at A, Fig. 222, i.e., the face of the cutting edges being inclined 5 degrees and the leading edge 25 degrees, making the angle of the cutting edge 60 degrees, which proved to be a very effective construction, the cutter a enlarging the hole to the extent of taking out about half of the stock and the cutter b removing the remainder.
The spindle was then reversed and the operation continued from the opposite end until only a small portion of the 2-inch hole was left to guide the boring bar. The bar was then withdrawn and a disk e fitted to it. This disk was 5 1/8 inches in diameter, so as to just fit the enlarged hole and furnish a guide for completing the enlargement of the hole, as shown in the lower illustration.
The work was successfully done, a true, smooth hole bored, the two sections of which coincided perfectly. It will be noted that in this job the hole was very large in proportion to the exterior diameter, and a large amount of stock was taken out; in fact, nearly 350 pounds of hard steel. This was removed at the rate of nearly 30 pounds per hour.
The plan will doubtless commend itself for similar work, and where there is even a greater difference between the directing hole and the finished bore three or more cutters might be used to advantage.
It is frequently the custom to fit flat cutters in elongated mortises made through the bar instead of using a round cutter in a bored hole. The flat cutters will be proper when the boring bar is comparatively small in diameter, as it weakens the bar less than a round hole of sufficient diameter to carry a cylindrical cutter of the proper strength. Still the cylindrical cutter should be used whenever possible, both for rigidity and cutting qualities as well as economy.
When large holes are to be bored a cross arm is used carrying a cutter on each end. Sometimes two cutters on each end are used, a roughing and a finishing cutter.
Sometimes a large hollow boring bar is used, carrying a crossbar or head with two tools. This cross bar is arranged to slide on the boring bar and is fed forward by a screw passing through the center of the bar and having upon it a nut that is connected with the cross head. Such an arrangement is used for boring engine cylinders. These boring heads are often driven by the old "star-feed" arrangement, familiar to nearly all machinists.
These elaborate devices for boring are usually constructed for special boring machines and may hardly be considered as a part of the equipment of an engine lathe.
Milling may be successfully performed on a lathe by strapping the work to the compound rest, to the carriage or to a suitable fixture attached to either. While not so economical or so rapid as on a regular milling machine, it often proves very advantageous when a milling machine is not at hand or when the machines of the shop are crowded with work so as not to be available.
Many light operations of milling may be performed on a speed lathe, with proper fixtures for the purpose, particularly when the work is of brass or similar soft metals. In these cases the speed lathe will often turn out as much work as the plain hand milling machine.
Gear cutting can frequently be done on the lathe under similar circumstances to those referred to above. The necessary fixtures for holding and indexing the work may be comparatively simple and economical, a change-gear being frequently used as an index, and many jobs quite satisfactorily done in the absence of a regular gear-cutting machine.
Grinding is a common operation in the lathe and is referred to in the chapter on lathe attachments.
In the absence of a suitable machine designed for the purpose, cam cutting may be successfully done in the lathe, by the use of proper formers. The milling cutter for such operations is carried in the center hole of the lathe spindle, and the cam held by a suitable fixture attached to the compound rest, or to the carriage, as may be most convenient.
The work may thus be arranged so as to cut face cams or edge cams, and to mill the cam slots of irregular contour on either edge or face cams.
However, the question of cams is one of such great variety, and the devices necessary to properly handle them are so many, a detailed discussion of ways and means for doing the work does not seem proper in this place.
The practical and resourceful machinist will find many uses for the engine lathe that have not been here described, and if he is a progressive man he will discover many new uses and new devices for handling the many new kinds of work with which he will be confronted.
Whatever new and improved machines he may have available, or however well they may be adapted to his many wants, his principal dependence will be likely to be, in the future as in the past, on the engine lathe, "the king of machine shop tools."