Milling

“ In milling to a given thickness or size, the most accurate results are ordinarily obtained by straddle mills or side milling cutters; for when only one side is milled at a time, and the piece has to be changed from one side to the other, it is hardly practicable to work to a smaller limit than two -thousandths of an inch. Side milling frequently requires more attention to keep the work smooth than ordinary surface milling. ”

“ This primitive form of milling, whose adoption constituted the first step in the art, still survives among certain peoples of rude civilization. The second step in the development of milling processes was taken when for the mortar and pestle were substituted two roughened grinding surfaces, placed close together, between which the grain was reduced to powder. ”

“ Milling, as we have already explained, is a process that cannot be governed by any fixed set of rules, but there are a few general instruc- tions which, if carefully followed, will enable the machine to be more efficiently operated and largely influence the success that is attained. ”

“ Much time is lost in operating a milling machine that is inconvenient in any way for the workman to handle: therefore, from the standpoints of economy and efficiency, convenience is a most desirable quality. ”

“ Speeds and Feeds. It is rare that the conditions surrounding any two jobs on a milling machine are the same. Sometimes the work is of the heavies class to which the machine is adapted, requiring gangs of cutters operating at a comparitively fast speed and coarse feed; again it is of a lighter type, requiring only one cutter operating at a fast speed and fine feed. The shape of the piece sometimes demands that the cutter be fed through faster or slower than would ordinarily be done in milling a plain surface. ”

“ The development of the manufacture of milling cutters, and a better understanding of their care and use, have resulted in a rapid growth in the number and variety of milling operations, and a corre- sponding increase in the sizes and varieties of cutters. ”

“ All of the important alignments in milling machines are obtained by scraping, a process consisting of going over the different bearing surfaces by hand with a chisel-like tool, and removing the highest spots until a maximum number of bearing points is secured. ”

“ When spirals cannot be conveniently cut with side or angular milling cutters, as previously described, it is sometimes convenient to use end mills, as for example, when the diameter of the piece is very large, or the spiral is of such a lead that the table cannot be set at the requisite angle, the work is so held that its centre and that of the mill will be in the same plane and the saddle is set at zero. ”

“ Plain Milling Machine. The word plain when applied to any milling machine is used to designate one in which the longitudinal travel of the table is fixed at right angles to the spindle. Both manufacturing and planer types are therefore essentially plain milling machines.
An illustration of a plain milling machine of the column and knee type is shown on page 19. In this machine, the table has the three movements: longitudinally, transversely, and vertically, that have already been mentioned. Some machines have both power and hand feeds for all three of the movements ”

“ From the days of Oliver Evans, the first American mechanic to make any improvement in milling machinery, until 1870, there was, if we may except some grain cleaning or smut machines, no very strongly marked advance in milling machinery or in the methods of manufacturing flour. ”

“ Centre cut end mills are used for milling shallow recesses in a surface where there has been no hole previously bored for starting the cut, for milling squares on the ends of round shafts, and other similar work. This form of mill has fewer teeth, and is, therefore, better adapted to taking heavy cuts than the regular solid or shell end mills. Slotting end mills with two lips, or cutting edges, are especially adaptable to fast milling of deep slots from the solid where there has been no hole previously drilled for starting the cut. ”

“ Oil Can or Pump and Tank. Every milling machine must be fitted with some arrangement for lubricating the cutters when working on steel, or wrought iron. Either an oil can or a pump and tank are employed for this purpose. ”

“ With vertical spindle milling machines, when a cutter is working on a flat surface, it does not matter which way the table is fed, but if the cutter is milling a side of a casting, as well as a flat surface, the table should be fed in the opposite direction to that in which the cutter revolves, for the reasons already mentioned. ”

“ Following the milling machine, came the grinder, in which a revolving wheel of an abrasive material served to wear away the surface of a piece of work, and with this form of machine steels of great hardness could be finished with accuracy and a high polish. ”

“ Essentials of a Modern Milling Machine It has been previously stated that the foremost advantages attending the employment of the milling machine are, the production of a great variety of work, and the exact duplication of pieces at an economical cost. In order that these advantages may fully materialize, it is necessary that many requirements be fulfilled in the design and construction of the machine. ”

“ The milling tool, as it revolves, is allowed to swivel so as to accommodate itself to the oval. When the bevilled edge has been formed, the first milling tool is removed and another substituted while the work revolves. ”

“ Broadly speaking, the variety of attachments for use on milling machines is almost limitless. To fully realize this, one has only to visit several shops producing different kinds of work on milling machiens, and observe the methods employed. Devices of every conceivable description will be seen in use in connection with the machines, and, while many of them may be of a more or less special character and adaptable only to a particular operation, they are, strictly speaking, attachments. ”

“ The outline is cut from the solid, and the material is steel, hence the cut is a heavy one. Lard oil or soda water is used as a cutting lubricant.
Milling End and Slot in Spiral Head Work Drivers on a No. 3 B Heavy Plain Milling Machine
Several of these work drivers are placed in the special fixture shown and clamped by means of the set screws at the side and end. ”

“ When any difficulty is encountered in obtaining the right combination of speed and feed, it is well to seek the advice of the foreman in charge of the job, or that of a widely experienced milling machine operator. ”

“ In order to obtain the highest degree of efficiency in milling machine construction, it is necessary that the utmost care be taken in designing the different parts, selecting materials, and in the quality of workmanship in building. ”

“ In order to be economical in operation, a milling machine must have ample ranges of spindle speeds and table feeds, and plenty of power, so as to adapt it to the many varieties of work. Further, its efficiency must be high, and its parts must be conveniently arranged to allow quick manipulation and ready adjustment. The third general requirement, durability, is, to a great extent, dependent upon the design and quality of materials that enter into the construction of a machine. ”

“ If a horizontal spindle machine is employed, and the work is clamped to the table, plain cutters of unusually large diameter are required, and when a face milling cutter is used, the work must be clamped to a knee. ”

“ It is evident, therefore, that the selection, care and use of milling cutters are points of utmost importance in attaining success in the process of milling. The failure to obtain commercial results may often be attributed to the fact that the wrong cutter has been used on a certain job, or even if the right cutter has been chosen, the work has not been done under the most favorable conditions. ”

“ Interlocking inserted tooth milling cutters, 8 inches in diameter, are used, the large diameter being necessary because of the height of the casting at the ends.
Where the end thrust on the arbor cannot be equalized, the greatest thrust should be toward the spindle nose. Thus in the above operation, two right-hand angle cutters are used against one left-hand, and the greatest thrust is toward the spindle nose.
Surfacing Large Casting on a No. 4 B Heavy Plain Milling Machine
An excellent example of heavy, plain gang milling is shown in this illustration. ”

“ In the most advanced mills which use the new process, the bran is reground and the tailings from the coarse middlings, containing germ and large middlings with pieces of bran attached, are crushed between two rolls. These can hardly be counted as reductions, as they are simply the finishing touches, put on to aid in working the stuff up clean and to permit of a little higher grinding at first. Regarding both old style and new process milling, you are already posted. Gradual reduction is newer, much more extensive, and merits a much more thorough explanation. ”

“ We are able to machine the earth in much the same way as a piece of metal is machined in the machine shop. In fact, the drill, [252] the circular saw, the slotter, and even the milling machine have their counterpart in the excavating machinery of to-day. Of course we cannot expect to find the counterpart of such machines as the lathe, boring mill, and planer, in which the work revolves against the tool, because this planet of ours is rather too big a piece of stock to be placed between lathe centers or to be bolted to a planer bed. ”

“ The horizontal boring, drilling and milling machine is very efficient for certain classes of work because it enables all the machining operations on some parts to be completed at one setting. To illustrate, a casting which requires drilling, boring and milling at different places, can often be finished without disturbing its position on the platen after it is clamped in place. Frequently a comparatively small surface needs to be milled after a part has been bored. ”

“ In the cutting of metals the work may move against a fixed tool or the tool may move against a fixed piece of work. In a lathe, it is the work that revolves or rotates against the tool. In the drill and the milling machine the tool revolves against the work. ”

“ The workpiece moves continuously, slowly, during operations while the rotating milling cutter shaves or saws the surface being worked. The milling machine is usually used to make rectilinear cuts to form accurately related plane surfaces or grooves. ”

“ This is owing to the fact that up to that time the milling machine had not become so extensively used for manufacturing purposes. In this field it must be capable of not only producing accurate work of high quality, but of producing it rapidly. The more rapidly a machine is operated, the greater is its tendency to vibrate. This is further augmented by the use of cutters made from high speed steel, for they can be made to take unusually heavy cuts at fast speeds and coarse feeds. ”

“ In construction, spiral heads of today embody the same principles as the one on the original universal milling machine, but improvements have made them more solid and convenient to operate. Likewise, improvements have been made in the design and construction of the foot-stock.
Since our spiral head is typical of these mechanisms, a description of its various points may aid in understanding the methods of indexing and cutting spirals. The head itself consists of a hollow, semi-circular casting in which is mounted a spindle that is connected to an index crank through a worm and wheel. Fig. ”

“ All milling machines are equipped with some support for the outer end of the cutter arbor. The adjustable centre shown at A is one form that is used for lighter classes, or work where an arbor with a flat tenon is employed. The centre serves to support the outer end of the arbor and helps to keep the flat tenon in place in the slot in the spindle. ”

“ Limits in Milling to Size. The limit for error in size to which work should be milled depends entirely upon the character of the job. With some work, a limit of one-hundredth of an inch is plenty good enough, while many other pieces must be finished to within one-thousandth of an inch of being exactly parallel or straight, as the case may be. ”

“ In milling machines the work is machined by revolving vertical or horizontal serrated cutters, which produce a fine finished smooth surface. These cutters can be shaped, or two or three of them put together, to mill out irregular curves and grooves, and so save a vast amount of labour formerly required from the fitters. ”

“ It is singular, that with the immense variety of tools set forth in the preceding chapter, how few, really, require the art of the workman to grind and sharpen. If we take the lathe, the drilling machine, as well as the shaper, planer, milling machine, and all power-driven tools, they are merely mechanism contrived to handle some small, and, apparently, inconsequential tool, which does the work on the material. ”

“ The operation of milling was always performed by women, and the method thereof was by rubbing the clumsy pestal round and round on seed in the hollow slab, with, of course, an occasional thump or two. ”

“ It may thus readily be seen that it is the little bar of metal from which the small tool is made that needs our care and attention.
This is particularly true of the expensive milling machines, where the little saw, if not in perfect order, and not properly set, will not only do improper work, but injure the machine itself.p. 27 More lathes are ruined from using badly ground tools than from any other cause.
In the whole line of tools which the machinist must take care of daily, there is nothing as important as the lathe cutting-tool, and the knowledge which goes with it to use the proper one. ”