The designer of lathes. The manufacturer’s view of a lathe. The proper medium. Cause of failure. The visionary designer. Conscientious efforts to improve in design. Design of the lathe bed. Elementary design. Professor Sweet’s observations. The parabolic form of lathe beds. The author’s design. Form of the tracks. Bed of the old chain lathe. The English method of stating lathe capacity. Method of increasing the swing of the lathe. The Lodge & Shipley lathe bed. Uniform thickness of metal in beds. Ideal form of bed. Cross-ties, or bars. Four Vs. Flat surfaces. Lathe bed supports. Height of lathe centers. Wooden legs for lathe beds. An early form of braced, cast iron legs. Cabinets or cupboard bases. Old style cast iron legs still in use. Form of cabinets. Principles of the design of cabinets. Cabinets for small lathes. The Lodge & Shipley cabinet. The Hendey-Norton cabinet.
To the experienced and conscientious designer of machine tools the condition is frequently forced upon him that it is often easier, and usually far more agreeable, to design machines as he really believes they should be, than to design such machines as will meet the popular requirements of the market. He may be sure that a certain plan would make really a better and more efficient machine, yet he must, from the outset, consider the kind of a machine the customers want and will buy and pay for, since they are, as has been often said, “the court of final resort” in the matter, and machine-tool builders manufacture machines to sell, and not for the purpose of exploiting individual opinions, however good they may be, or the fads and fancies of draftsmen who are sometimes imbued with visionary and impractical ideas.
The manufacturer himself may be perfectly sure that the machines he is turning out are not the best adapted for the purposes for which they are used, or the best he could build for the money. He may so far have the courage of his convictions as to build for his own use machines quite different from those he manufactures for his customers. Yet for sale he must build what his customers want with small regard for his own personal opinions.
By this it is not meant that the builder does not use his judgment in a mechanical way, or that he does not endeavor to build the best machines possible, inasmuch as he does give this very question much time, attention, and study. Yet he must, from the very nature of the case, always keep in mind the question, “What will the customers think of this new machine? ” ” Will this device be a success, or will it prove a failure?” Some machines that have been put on the market with feelings of much trepidation have proven great money-makers, while other machines possessing much mechanical excellence have fallen flat and a large majority of the customers refused to endorse them. The author has seen many such cases, and this has probably been the experience of every man who has designed and built machine tools.
The proper medium in the matter seems to be to keep as closely in touch as possible with the purchasers of machinery; to ascertain their needs and preferences as closely as may be; to anticipate their wants when possible, but at the same time with conservatism; and to avoid putting entirely new devices on the market until they have been thoroughly tested in the home shop and by a few friendly shops outside of it. And by entirely new devices is meant substantially new and complete machines, as the builder will frequently have parts of, or attachments to, the regular line of machines that are made to the order of a particular customer and that e feels perfectly sure of being well suited to the work that it is expected to perform; yet in these cases considerable caution is necessary.
The one fruitful source of difficulty, disappointment, and failure to be most avoided in the production of new devices is the mania often manifested by designers to produce something absolutely new, decidedly novel, the like of which no one has ever seen or dreamed of, and that will startle the mechanical world, revolutionize the business, and prove its author a veritable Napoleon of mechanical science.
When confronted with such a man or such a condition, the wiser course will be to abandon such ambitious attempts to eclipse all previous efforts, get down out of the clouds, design something of practical utility, even if it is not strikingly new; something that past experience gives some guarantee of success; something that will surely bring the proper financial return and be a credit to the shop. It is always well to remember, when tempted to go off on a tangent after something new and marvelous, that “a good adaptation is better than a poor original,” and that when Solomon said that “there is no new thing under the sun,” he did not come far from the truth, since many of the things we think are new may be found in almost the identical form, that have been invented, used, and discarded years ago, as the records of many mechanical libraries as well as the United States Patent Office will furnish abundant evidence.
By the foregoing remarks it is not intended to discourage originality, original thought and research, or the proper ambition to improvement, for we often produce more of real value by the effort to evolve mechanical improvements than by the design of entirely new machines, and the studious and observing designer will always be on the alert to devise improvements upon existing forms and processes.
These observations and suggestions apply with as much force in the efforts to improve the lathe as any other machine in common use. Being the oldest machine in the machine shop does not in any respect limit the field for improvements in it. Neither does it preclude the design of entirely new machines that may have, perhaps, very little of the characteristics of a lathe, although we must necessarily be confined to the essentials heretofore discussed, namely, a bed, upon which rest the head-stock, tail-stock, and carriage, or their equivalents, if we would claim that our machine is a lathe.
With these preliminary statements relative to the conditions and requirements of good and successful designing, we may take up the designing of lathes somewhat in detail and inquire into the design of the individual parts and groups of parts, giving some of the ideas of men prominent in this field, and adding such comments and suggestions as seem proper and pertinent to the case as the matter is proceeded with.
In carrying out this plan it will be natural to commence with the bed, considering its use and purpose, and the proper form to fulfil the requirements of this particular part.
The lathe bed, considered in an elementary way, and in the case of a lathe of moderate length, may be taken as a beam, supported at each end and in its turn supporting at one end the headstock, at the other end the tail-stock, and in the center the carriage, as represented in Fig. Elementary Form of Lathe Bed.
This being the problem, and as the head-stock and the tailstock stand directly over the legs or supports, we might consider the problem as that of a beam loaded at the center, which would naturally suggest that the under side of the bed instead of being straight should be a parabolic curve. This would result in the form shown in Fig. Parabolic Form of Lathe Bed, which would, if the carriage was stationary,
conform to the conditions of the problem. But, while the carriage is not stationary, it is located at what would normally be the weakest point along the length of the bed, namely, a point farthest from either support. So far the parabolic curve, then, is correct.
But while we have been placing our supports at the extreme end of the bed we have no condition of the case which makes it incumbent upon us to do so. In other words, we may add a portion to each end of the bed, outside of, or beyond the line of these supports, in the form shown in Fig. Modified Parabolic Form of Lathe Bed, showing a modified form of the lathe bed, the extensions at each end being in the form of a beam supported at one end. Theoretically, then, this would seem to be the proper form of a lathe bed in order that it might conform to the necessary requirements as to form and its ability to sustain the usual weights and strains to which it will be subjected, and at the same time not be of excessive weight, which would entail unnecessary expense.
This is substantially the view taken by Prof. John E. Sweet in reference to machine beds. He says:
“No reasoning can make it out that the place for the support of an ordinary sized lathe bed at the tail-stock end of the lathe is at the end. If placed a considerable distance from the end, and the tail-stock is at the end, it is better supported than when in the middle of the present style of lathes and also better supported at
all other points. At the head-stock end it is quite a different matter as the head-stock is always fixed and is usually heavier loaded, exclusive of its own greater weight. Where the head-stock end support is a closet, there is no way to make it look right except to have the closet the same width as the head-stock is long.
“In the case of a planing machine bed up to 12 or 15 feet in length there is no reason for having three pairs of supports. Unless the foundation is absolutely unyielding a thing that is more rare than the other kind the three or more pairs of supports are especially bad, and to attempt to hold the foundation true with a frail planer bed is foolish. The distance between the supports in Fig. Prof. Sweet’s Form of Bed, supported at Two Points only is no greater than in Fig. A Common Form of Lathe Bed, Supported at Three Points, and as in no case would the center of the load in planing overhang the supports more than a slight distance the style shown in Fig. Prof. Sweet’s Form of Bed, supported at Two Points only is quite as well supported as the other; and when the iron in the legs and the work to fit them are taken into account, if they were all put into the casting the bed could be brought down to the floor as in Fig. Prof. Sweet’s Design Applied to a Planer Bed, greatly improving the structure.
” Another improvement is to use the iron usually put in the cross-
girts which do not stiffen the bed in any way to any great extent and use it in bottom and top webs, making the thing a four-
sided box, which is from four to a dozen times stiffer in all directions, and then rest the whole thing on three points, one under the
back of each housing and one under the middle toward the other end. The whole thing, including patterns and setting, will cost no (or very little) more and be four times better than present practice.
“If the bed is supported at the same points when it is planed and fitted up, no attention or skill is required in the erection just set it anywhere and on anything solid, and that is all that need be or can be done.”
There is “meat for reflection” in what Professor Sweet says (as there usually is), and the principle upon which he makes his deductions is undoubtedly correct.
To render the comparison more apparent and in a practical manner the two views shown in Figs. The Parabolic Design of a Lathe Bed and The Rectangular Form of Equal Strength are given. In
Fig. The Parabolic Design of a Lathe Bed the parabolic design is shown in proper proportion for supporting the head-stock, tail-stock, and carriage, and the proportions laid out are ample for all purposes, as is also the supports and their distance from each other. In Fig. The Rectangular Form of Equal Strength is shown a rectangular design of bed of like length and of sufficient depth to give the requisite strength, provided there is a central support added to prevent a sinking in the center of the bed, as the distance between supports would otherwise be too great. While nothing has been added to the strength or the stiffness of the bed, we have been
obliged to add the central support and in addition to this the weight of the parabolic form of bed is 1,390 pounds, while the rectangular form is 1,550, a very material addition without compensating advantages; and at the same time we have the disadvantage referred to by Professor Sweet, that the nearer together we can get the supports and still retain the condition of rigidity the less we shall have to depend upon the correctness of the foundations, and this of itself is a matter of very important consideration, since in some of the popular forms of machines their truth and correctness depends to a very considerable extent upon the accuracy and continued stability of the foundations upon which they rest.
It was from such considerations and conditions as has just been illustrated and described that the author designed and built the 21-inch swing engine lathe shown in Fig. A 21-inch Lathe with the Parabolic Form of Bed. This lathe met with exceptional success in the market both in a mechanical and financial way and a large number of them were built and sold, although they were brought out during a season of great depression both in mechanical and financial circles, when hardly a machine
shop in the country was running full time, and many of them but eight hours a day for three days only in a week. After a couple of years these beds were changed to the rectangular form in order to satisfy the demands of customers, the depth being nearly as great as the one here shown is in its deepest part, and the weight much increased. The ends were made square and the rear box leg made a regular cabinet similar to the front cabinet. The lathe is still built with very little change in its general design except as above specified, although it was originally designed over a dozen years ago.
It will be noticed in the design shown in Fig. A 21-inch Lathe with the Parabolic Form of Bed that the front end of the front cabinet is in a vertical line with the front end of the head-stock, as suggested by Professor Sweet, and about twelve years before his article was published, although it is probable that he had held the same opinions therein expressed for a much longer period than this would indicate.
There is much diversity of opinion as to the proper method of designing the “shears,” “ways,” “tracks,” “Vs” or by whatever term we may designate the top portion of a lathe bed.
It has been shown in the “old chain lathe,” Fig. Front Elevation of Old “Chain lathe”, when beds were made of wood, that the Vs were made of strips of wrought iron set on edge and fastened in rabbits cut in the wooden bed, their upper edges chipped and filed in the form of an inverted V. There were only two of these, the head-stock, tail-stock and carriage, all resting upon the same Vs. Consequently, the carriage was not able to run past the head-stock or the tail-stock, as is the case with the modern lathe-bed having four Vs..
The usual form of construction is shown in cross section in Fig. The Usual Form of Cross Section of Bed with Four Vs, which is drawn to the usual proportion of the component parts of a bed. As a matter of strength, stability, and rigidity, the center, at the top, of the inside Vs A, A, and the lathe center or center of the head spindle B, should form an equilateral triangle. An arc C, of a radius struck from the center B, and just clearing the V at A, will be the radius of the swing of the lathe.
This matter of determining “the swing” of a lathe differs materially as between the practice of this country and England. An English author, Mr. Joseph Horner, states it thus: “The ‘centers’ signifies the distance from the top face of the bed to the centers of the spindles. English and continental lathes are designated thus, but American by twice the centers, or the ‘swing’ in other words the maximum diameter which a lathe will carry over the bed.” And with all due respect to the opinions and practice of our cousins “on the other side,” it would seem the proper designation, and the one in which a prospective purchaser would be most interested, to tell him how large a piece of work could be done in the lathe, rather than to tell him the half of this diameter, or the radius, and let him have the trouble of the mental calculation of multiplying this dimension by two every time it is mentioned. It may seem all right when one is accustomed to it, but, like the English monetary system of pounds, shillings, and pence, it seems unnecessarily cumbersome when compared with the directness of the American expression.
In order to increase the swing of the lathe without raising the head spindle in relation to the bed, some builders prefer to omit the inside V’s, as shown in Fig. The English Form of Bed with only Two V’s, by which means the arc C, as given in Fig. The Usual Form of Cross Section of Bed with Four Vs, and here shown as a dotted line, is increased to the arc D, and the swing of the lathe increased by twice this difference. In this case the headstock and the tail-stock are both fitted to the flat top of the bed and also have a projecting rib or its equivalent built down and fitted to the inside of the inwardly projecting flange of the top of the bed. This method of construction is that in use in English and continental lathes and in recent years has been adopted by some lathe builders in this country.
Still another method for increasing the swing is shown in Fig. Bed with Depressed Inside V’s, giving Increased Swing. This is by lowering the inside V’s, upon which the headstock and tail-stock rest, and leaving the outer V’s supporting the carriage in their original position. In this engraving the arcs, representing the radius of the swing in the two former examples, are shown in dotted lines, and the increased arc E by a full line. There are other advantages in the form of construction shown in Figs. The English Form of Bed with only Two V’s and Bed with Depressed Inside V’s, giving Increased Swing, which will be noticed later on.
In Fig. The Lodge & Shipley Form of Bed is shown the form of bed adapted by Lodge & Shipley, which will be seen to be a modification of the preceding examples in that, in this case, the English form of a flat surface is used in place of the front V, while at the rear the inverted V-shape is retained. There are several advantages in this form. The rear V is preferred by some as a better method of locating the headstock and tail-stock in perfect alignment, inasmuch as that while the head-stock, once located and securely bolted down, remains in its fixed position whether resting on V’s or upon a flat surface and
between vertical faces as in the English lathe. With the movable tail-stock this is different. There is a constant tendency to wear in all directions of contact, and if fitted between vertical surfaces this tendency will in time throw it out of line. When resting upon the inclined surfaces of the inverted V, the wear is likely to be equal on the two sides and the lateral alignment is maintained, while the vertical wear will be considerably less than that of the head spindle in the boxes, which should be vertically adjustable to compensate for this wear and so a proper and perfect alignment of the two be maintained.
The bed shown in Fig. The Lodge & Shipley Form of Bed is considerably deeper than the former examples, but corresponds very nearly to the proportions that have been found necessary to the -proper strength and rigidity of the modern lathe when used under the severe strains and hard usage incident to modern shop methods. and to the use of high-speed tool steels, with the necessity for the rapid reduction of the diameter of the stock which would in former times have been considered very wasteful of materials, but which in these days of cheap machine steel are much more economical than the usual processes of forging the parts to nearly the diameters necessary, as was formerly the usage when the price of steel was very much above what it is now and the cost of labor considerably less.