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.
Design of head-stock for wooden bed lathes. Early design for use on a cast iron bed. An old New Haven head-stock. The arch form of the bottom plate. Providing for reversing gears. The Hendey-Norton head-stock. The Schumacher & Boye head-stock. The Le Blond head-stock. The New Haven head-stock. The arch tie brace of the new Hendey-Norton design. Generalities in describing a lathe spindle. Designing a spindle. Governing conditions. The nose of the spindle. Spindle collars. Proper proportions for lathe spindles. Large versus long bearings. Design of the spindle cone.
The subject of lathe design is continued by the consideration of the design and construction of the head-stock, which in some respects is the most important part, and with it and the parts which go to make up the complete head-stock, the most important group of parts in the lathe.
In the earlier form of lathes this piece was, like most of the other parts, simple and crude in design as well as in the workmanship bestowed upon it. It generally consisted of a base and the two upright ends in which provision was made to receive the boxes, and when wooden beds were thought sufficient for a lathe a strip was added beneath that filled the space between the two timbers forming the bed. Such a design for a head-stock is shown in Fig. 54, which is taken from an old lathe that did many years' service in a general repair shop. It will be noticed that the housing for the spindle boxes do not have square edges, but are of V-shaped form. They were finished with a file only and the boxes made of cast iron, filed to a fit and lined with babbitt metal which was said to have been poured around the lathe spindle after it was finished, set in place, and lined up as well as might be with the crude appliances at hand. The top portion of the boxes were held down by a straight bar cap with two holes which fitted over fixed threaded studs that had been cast into the head-stock for this purpose.
The lathe was devoid of a back gear and the spindle carried a three-step cone, the largest part of which was as large as was possible to get into the head, and a belt quite wide, considering the power then thought necessary to drive a lathe carrying the diminutive chip which was considered proper for a lathe to take at the time this lathe was in use.
Later on, when the cast iron bed was adopted and when back gears were added to the lathe, the requirements of additional strength were recognized and not only the base plate, but the uprights or housings at the front and rear end, were made thicker and heavier. One of these head-stocks is shown in Fig. 55, which gives a good general idea of the form of the casting and shows also a strengthening brace A. While it would seem at first thought more necessary to brace the housing of the front box than that carrying the rear journal, it should be remembered that the latter must withstand the strain of the "thrust" or endwise pressure of the spindle due to holding work upon centers, and the pressure of drilling work, one end of which is held in a chuck and the other in a center rest, and similar kinds of work. While in the modern lathes this thrust device is usually a part of the rear box, the earlier method was to fix two studs in the rear of the head-stock, one in each side of the rear box and on a horizontal line with it, and across these to fix a strong bar carrying an adjustable thrust screw for taking the end thrust of the spindle. The details and design of this important device will be taken up further on.
Fig. 54. - Early Form of Head-Stock for Wooden Lathe Bed.
Fig. 55. - A Later Form of Head-Stock with Back Gears and a Strengthening Brace.
In Fig. 56 is shown a peculiar form of head-stock upon an old lathe in one of the older shops in New Haven, Conn. The lathe was broken up for old iron after an indefinite period of idleness. It was of about 16-inch swing and the various members of the head-stock were about one and one-half inches square. The bed of the lathe, and the legs which supported it, were of cast iron and very-much like those shown in Fig. 46. The head was provided with back gears of very light design and the lathe had a lead screw and feed-rod adapting it for thread cutting. It was undoubtedly considered a proper engine lathe "in its day."
Fig. 56. - Form of Head-Stock on Old Lathe found in New Haven, Conn.
The next form of head-stock which followed that shown in Fig. 55 seems to have been of the form shown in Fig. 57. In this case the base of the casting was raised in arch-like form and the under side recessed to the same form so as to maintain an equal thickness of metal throughout. This form seems to have been a favorite one and many lathes were built by various makers with substantially this form, the variations from it not being of sufficient importance to justify a further classification.
As yet the housings had not been made thick enough to suggest coring them out in order to save iron or for the purpose of avoiding unequal contraction of the metal upon cooling after casting, by making all members of the casting of as nearly an equal thickness as possible. Of late years these points have received much attention and study by the designers of machine tools, and rightly so, as their importance was to a large extent overlooked in the earlier designs, the reason probably being that all castings were made so much lighter and had much less strain to withstand in the regular service to which the machine was put.
Fig. 57. - One of the Older Favorite Forms of Head-Stock.