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.
In Fig. 58 is shown a modification of the arch form shown in Fig. 57, which has for its purpose the strengthening obtained by the rib A in Fig. 55, only in a better form, as the method is "cored out," or formed with a "green sand core" under the head-stock, so as to provide for an equal thickness of metal over the entire base. This raised portion could be introduced quite conveniently as the small end of the spindle cone was located over it, thus insuring ample space for building it up.
In the examples thus far shown of lathe heads the feed gears were located outside the housings, except in the case of that shown in Fig. 56. As the change came to be made of locating "tumbler gears," or reversing gears, inside of the housing, it naturally followed that the metal of the head-stock base must be cut away under that part of the main spindle upon which was fixed the spindle gear or feed gear from which the feed mechanism was driven. This was the case for perhaps fifty years, and at the present time, now that reversing devices are constructed as a part of the apron mechanism, the feed gears may be placed outside of the housing, although some good builders still keep it inside and connected in practically "the same old way," even if the "yoke gears" or reversing gears are omitted.
Fig. 58. - Another Form of Strengthening Brace.
When reversing gears were thought necessary to be upon the inside of the housing, a hole was cut out for them in the raised arch A, Fig. 58, and this practice was followed in any head-stock having this or a similar obstruction to these gears, and provided, of course, that they were to be located inside of the rear housing.
One of the recent modifications of the above form is that shown in Fig. 59, which is a type of the Hendey-Norton manufacture. The central figure is a front elevation with the sectional form indicated by dotted lines. The figure at the left is a rear end elevation with the internal form on the line A, A, of the central figure, while the figure on the right is a similar elevation of the front end with dotted lines showing the section on the line B, B.
It will be seen that the portion of the base on the line A, A, is of arched form, somewhat as shown at A, Fig. 58, while the form at the line B, B, is of an inverted arch, or as frequently called by the shop men a "pig trough" shape. This latter form enables the metal to be carried higher up at the front and back while the center is depressed to give proper clearance for the larger steps of the cone and the face gear. At the lowest part of this depression there is usually an opening through which oil may drip so as not to collect inconveniently at this point. The arch-like form near the rear housing adds very much to the strength and rigidity of the casting. It will be noticed that in this design the main spindle boxes are not "capped in," that is, held down by removable caps. More will be said of this peculiarity in describing boxes and spindles.
The cores beneath the base are carried up into the housings in many of the modern head-stocks as far as possible, and still leave ample support for the boxes and spindles. The advisability of this method of lightening the weight of the casting is still an open question among machine tool designers who have endeavored to avoid unequal strains in the shrinkage of castings by making all members of as nearly equal thickness as possible. Sometimes this idea is carried too far and the result is liable to be that of sacrificing the necessary rigidity to prevent vibration, in the effort to follow out the ideal as to strains.
Fig. 59. - The Hendey-NortonForm of Head-Stock.
Fig. 60 shows a head-stock in which the inverted arch form is continued the entire length between the housings, but is carried upon a curved line as shown and forms a very graceful curve. The three figures are arranged the same as those comprising Fig. 59. The height of the curve might be greater at the line A, A, as will be shown in some others further on in this chapter, and the strength of the casting considerably increased.
This form is used with few modifications to adapt it to the diameters of driving-cones, the nature of the back gears and the feed gears and similar conditions that tend to somewhat alter the construction outlines of its design. This form seems to be a favorite one with designers, since among all the different builders and the variety of designs there are more builders using this form than all the others put together.
Fig. 60. - Form of Head-Stock built by a Majority of Lathe Builders.
While the above form of design carries a reversed curve for the top of the base, the form used by Shumacher and Boye, shown in Fig. 61, is of a single curve from rear to front housing and the inverted arch in its transverse sectional form. In this design the front and back is carried high up near the rear housing and comparatively low down near the front housing.
Fig. 61. - The Schumacher & Boyce Form of Head-Stock.
This is a design of much strength and rigidity in proportion to the weight of the casting, the metal being well distributed to resist heavy strains in the operation of the lathe.
The Le Blond type is shown in Fig. 62. In this we have a straight line at the back and front, with a modification of the reversed curve and the combination of the arch proper and the inverted arch as shown in Fig. 59. The form is pleasing to the eye, and the strength of the casting is quite sufficient for the requirements. In this case the housings are made of ample width, especially the front one. They are cored out inside so as to have substantially an equal thickness of metal at nearly all parts. The New Haven type of head-stock is shown in Fig. 63. In this case the inverted arch is used all the way through, but it is upon straight lines, that form a cross section at A, A, continuing straight and on a proper incline to a point near the line B, B, from whence it is horizontal.
Fig. 62. - The Le Blond Form of Head-Stock.