Brown & Sharpe Mfg. Co.

“ This is not the case, however, as experience has shown that a dull cutter wears more rapidly than a sharp one, and consequently one that is kept in good condition by frequent regrinding will invariably outlast one that is not so cared for. Besides, a dull cutter not only consumes more power, but cannot be operated as rapidly or take as heavy cuts as a sharp one, and the quality of the work is never as good. Too frequently in shops today, the efficiency of milling machines is impaired by the use of dull cutters, for no other reason than carelessness and negligence on the part of the operator. ”

“ Production costs are of vital importance to the shop owner, and no one factor influences them to a much greater extent than the efficiency of the different machines employed. Where this is low, the amount of power consumed for which there is no apparent return is higher than it should be, with the result that the cost of production is increased. It is essential, therefore, that a high degree of efficiency may be attained in the milling machine, so that a maximum amount of work may be produced for the power consumed. ”

“ The feed, inasmuch as it governs the output of work, is of greater importance than the speed of a cutter, and it is generally a safe rule to follow, that the speed should be as fast as the cutter will stand, and the feed as coarse as is consistent with good work. Much must be left to the judgment of the operator as to the correct speed and feed to use for the work in hand, and many cases will require repeated experiments before the best results are obtained. ”

“ There are so many good machinery oils upon the market that it is hard to specify any one as the best to use for lubricating a milling machine. Any good coal or mineral oil can be used. Never use an animal oil, as it will gum up the bearing surfaces, oil channels and tubes, and have a tendency to retard rather than render easy the movements of the different parts. It might also be said that in buying machinery oil it is always safest to purchase a lubricant of reliable quality instead of experimenting with the less expensive brands. ”

“ Milling is never a complete success where such conditions exist, and with the improved grinding machines and convenient means of removing and replacing cutters, there is no reason for limiting the capabilities of a machine by using dull cutters. Grinding a cutter takes only a short time, and the good results that are obtained, together with the economy assured, more than compensate for the time expended in grinding. ”

“ 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. ”

“ 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. ”

“ An operator should pay particular attention to clamping work on a milling machine, for the success of milling is more dependent on this than on would realize at first thought. It is an easy matter to place clamps on some work in such positions that the piece is sprung, consequently when the clamps are loosened and the piece resumes its natural shape, the milled surface is found inaccurate. Again, faulty clamping results in work becoming loosened during operation, and not only impairs the accuracy of the piece, but many
times damages the cutters and machine. ”

“ The cone drive machine is admirably adapted to all classes of work where it is not necessary to use combinations of extreme speeds and feeds. In these cases, however, it cannot fulfill the requirements. For instance, it is impossible to obtain a course enough feed for a cutter of very large diameter, because the feeding mechanism is invariably driven from the end of the spindle, and is subject to the speed variations of this part. ”

“ It is essential that the table of all milling machines used for manufacturing purposes, with the exception of the very smallest of the plain type, be fitted with both hand and automatic feeds. In the case of this exception, the work done is of such a small character that the machine can be operated more rapidly by hand than it could be if an automatic feed were applied. By the use of automatic feeds, one operator is enabled to run several machines on the majority of commercial work. ”

“ Plain milling cutters, side milling cutters, end mills, etc., are sharpened upon the tops of the teeth, while formed cutters of all kinds are sharpened upon the faces of the teeth. Modern cutter grinding machines are necessary where many cutters are employed, and are advantageous, even where there are only a few cutters used, for it is nearly impossible to properly resharpen cutters, except with a machine especially designed for that purpose. We illustrate at the back of the book the cutter grinding machines we build that are very suitable for use in connection with milling machines. ”

“ Seemingly small details in construction should receive careful attention, for it is these that many times give rise to serious trouble. The fitting of different parts, and making of all alignments should be carefully done, and means should be provided for taking up wear at any points where it is apt to occur. In connection with the wearing qualities of different parts, the selection of materials is an important factor; parts that are subject to continuous usage, such as the change gears in constant speed drive machines, should be made of a hard material having good wearing qualities. ”

“ In cutting the teeth, either the cutter should be stopped after cutting each groove and positioned so that the teeth will not scrape the sides and bottom of the groove, the table being returned by hand; or the knee should be dropped so that cutter will clear the groove just cut, and then run the table back to the starting point. Most mechanics prefer to stop the machine, for in dropping the knee, there is more liability of error, as the depth of cut has to be set for each groove, and this also takes more time than it does to stop the machine. ”

“ A good method of holding blanks is on arbors, such as our milling machine cutter arbors, that have a taper shank to fit the index spindle; the outer end of the arbor being supported by the foot-stock centre. Another way of holding blanks is by means of a shank arbor with expanding bushing, such as our gear cutting machine "work arbors." A nut is located on the arbor at each end of the bushing, one nut forcing the bushing up on the arbor and holding the blank, while the other pushes the bushing off the taper and releases the gear when finished. ”

“ Neither do we intend to describe the manner in which gears are cut on automatic gear cutting machines designed especially for that purpose. Our object is rather to give a few practical points applying to the cutting of different kinds of gears on a milling machine, and to show illustrations of how various gear cutting jobs and work of a kindred nature can be set up. ”

“ 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. ”

“ Consequently, when a large cutter is being used, the spindle is usually driven at its slowest speed, and the fastest feed that is then available is not coarse enough. Likewise, a correct combination of speed and feed cannot be had for a small mill, as this should run at the fastest spindle speed, and, when it does, the finest feed obtainable is much too coarse. The majority of work, however, does not require such combinations, and when medium-sized mills are used and work of ordinary classes is done, the cone drive machine is very satisfactory. ”

“ Different materials cannot be milled at the same speeds and feeds. Cutters of large diameter are employed for some jobs, and to get the proper peripheral speed, they must be rotated at a slower rate than those of smaller diameter. A finishing cut with the same cutter is usually taken at a faster speed, and correspondingly lower rate of feed per revolution of spindle than the roughing cut, in order to obtain a smoother finish. All these, and many other conditions, make it necessary that a machine have a wide range of spindle speeds and table feeds. ”

“ For machines that are used for light work and miscellaneous milling, an oil can is found satisfactory, as the amount of lubricant used is small and a pump and tank complicate the machine and make more for the operator to care for. When heavy and manufacturing milling is being done, however, and an abundance of oil is required, both to cool the cutters and wash out ships, it is not always practical to supply it through the medium of a can, as this cannot be made large enough to hold sufficient lubricant to last long. ”

“ 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. ”

“ Cutters or end mills with taper shanks and those which have end teeth, may be either right or left- hand, according to the direction in which the cutting edges of the teeth point. Taking an end mill for example, a right-hand mill is one which, held in the hand with the teeth away from you, presents the cutting edges of the teeth when revolved to the right or clock-wise. A left- hand mill is one that, similarly held, presents the cutting edges of its teeth when revolved to the left. Milling cutters having straight holes can be used either right or left-hand as desired. ”

“ The time required to replace tools in this way is more than offset by the advantage of being able to readily find them again; besides, the tidiness of a machine materially adds to the appearance of a shop.
It is well to remember when applying oil that ordinary bearings can hold only a few drops at a time and that this amount applied at regular and frequent intervals is far more beneficial than a flood of lubricant at irregular periods. It is a good practice to have one man attend to the oiling daily in shops where the machines are used by different workmen. ”

“ 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. ”

“ The belt and main driving pulley run at a constant high velocity regardless of the spindle speed, which is entirely dependent upon the ratio of gearing that may be in mesh. The power at the spindle is therefore constant, regardless of its speed. The mechanism of constant speed drive vertical spindle machines is essentially like that outlined above, except that a pair of bevel gears and vertical shaft are introduced to transmit power to the spindle head, from whence it is communicated to the spindle itself by spur gearing. ”

“ The worm wheel on the spindle contains 40 teeth and the worm is single threaded, hence for every turn of the index crank, theworm wheel is advanced one tooth, or the spindle makes 1/40 part of a revolution. This should be remembered, for it is used in all indexing calculations on the spiral head. If the crank is turned 40 times, the spindle and work will make one complete revolution. To find how many turns of the crank are necessary for a certain division of the work, 40 is divided by the number of the divisions which are desired. ”

“ 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. ”

“ If the material in the gear blank is expensive, it is sometimes advisable to make a cast iron blank to experiment with before cutting into the expensive material.
Fastening Blanks. Spiral gears are more liable to slip in cutting than spur gears. Small blanks may be dogged to the spindle, but the dog must be far enough from the blank so that it will not interfere with the cutter. For blanks that are more than three or four inches in diameter, it is better to use a taper shank arbor held directly in the spindle ”

“ The teeth of bevel gears constantly change in pitch from their large to small end, and for this reason it is impossible to cut gears whose tooth curves are theoretically correct, with rotary cutters having fixed curves, such as those used for cutting these gears on a milling machine. The cutter employed must be of a curve that will make the correct form at the large end of the tooth, hence it will necessarily leave the curve too straight at the small end. ”

“ By using different combinations of the change gears furnished, the ratio of the longitudinal movement of the table to the rotary movement of the work can be varied ; in other words, the leads of the spirals it is possible to cut are governed directly by these gears. Usually they are of such ratio that the work is advanced more than an inch while making one turn, and thus the spirals cut on milling machines are designated in terms of inches to one turn, rather than turns, or threads per inch; for instance, a spiral is said to be of 8 inches lead, not that its pitch is 1-8 turn per inch. ”

“ 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. ”

“ 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. ”