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.
Some of the refinements of detail noted in the Lodge & Shipley lathes for heavy cuts are shown at Fig. 335 as being of interest to the student of lathe construction. A light bridge will answer for light cuts on large diameters with the tool point directly above the front shear. But stresses are of a very different sort when the lathe is under a heavy cut on a small diameter.
Fig. 335. - Lathe Construction for Heavy Cuts.
The illustration A shows the position of tool and compound rest on the 24 inch Patent Head lathe when taking a 15 H. P. cut on work of 5 inches diameter. Heavy arrow indicates direction of pressure due to cut. Note the large bearing against the top and inside of bed directly in line with the tool thrust, in addition to the full length bearing of carriage upon front and rear V's. This extra bearing gives a solid support to the bridge just where it is needed, and positively prevents a deflection or distortion even under the heaviest cuts.
The sectional illustration at B shows why the tail stock will not back away from the work, no matter how heavy the cut. A pawl which engages the rack cast in the center rib of the bed furnishes a positive brace against end thrust. The four bolts for clamping the tail stock to the bed extend to the top of the barrel, where the nuts are easily accessible; and because of this construction the whole tail stock is drawn down solidly and evenly against the bed. The tail stock is massive in proportions and has long bearing on the bed. The barrel is large and permits long travel of the spindle. Floating plug binders lock the tail stock spindle securely and in correct alignment. The tail stock barrel is not split, but is always a correct reamed fit for the spindle.