Milling machine

“ 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 ”

“ 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. ”

“ Brown and Sharpe’s plain milling machine, or in other words a milling machine having but one feed motion, and therefore suitable for such work only as may be performed by feeding the work in a straight line under the cutter, the line of feed motion being at a right angle to the axis of the cutter spindle.
Machines of this class are capable of taking heavy cuts because the construction admits of great rigidity of the parts, there being but one slideway, and therefore but one place in the machine in which the rigidity is impaired by the necessity for a sliding surface. ”

“ The extended use of the milling machine, which is an especial feature of modern machine shop practice, is due, in a very large degree, to the solid emery wheel, which provides a simple method of sharpening the cutters without requiring them to be annealed and rehardened, it being found that annealing and rehardening reduces the cutting qualifications of the steel, and also impairs the truth of the cutting edges by reason of the warping or distortion that accompanies the hardening process. ”

“ 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. ”

“ 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. ”

“ 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 blank in this case is fastened on an ordinary lathe arbor mounted on the centres and dogged to the spiral head spindle.
In commercial manufacturing, gears such as that shown would be produced in quantities on automatic gear cutting machines, but where only an occasional gear is wanted, such as in replacing a broken one, it is advantageous to cut it on a milling machine. A new gear for a machine can usually be secured in this manner far quicker than it can be ordered and delivered. ”

“ 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. ”

“ And when no counter-shaft is used, the calculation is the same as abovce, except that the required speed and diameter of the machine pulley are substituted for the diameter and speed of the counter-shaft pulley.
Importance of Keeping Machine Clean and Well Oiled. Many workmen fail to appreciate the importance of keeping a machine clean and well oiled, and we cannot emphasize this point too strongly. Proper attention to these details influences the accuracy and efficiency of a milling machine and prolongs its life, while neglect to attent to these matters has ruined many a good machine. ”

“ 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. ”

“ Whenever possible, it is a good plan to have two sets of cutters, so that one set can be reground while the other is in use; the milling machine then need only be stopped long enough to change the cutters. ”

“ 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. ”

“ The word is also applied to many mechanical devices by which raw material is transformed into a condition ready for use or into a stage preparatory to other processes, e.g. saw-mill, rolling-mill, &c., or still more widely to buildings containing machinery used in manufactures, e.g. cotton-mill. In mining it is applied to various machines used in breaking and crushing the ore (see Ore-Dressing) .
In the engineering industries milling machines constitute a very important class of machine tools, the characteristic of which is that rotary cutters are employed for shaping the metal (see Tools) . ”

“ 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. ”

“ It was not until long after the planer had been invented that Eli Whitney, the American genius of cotton-gin fame, conceived the milling machine. He reversed the operation of the lathe by placing the cutting tool on the revolving spindle and sliding the work against it. Milling cutters consist of wheels formed with a number of cutting edges or chisels which are arranged either on the periphery of the wheel or on the face of the wheel. ”

“ 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. ”

“ 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. ”

“ On practically all of the Brown & Sharpe constant speed drive machines, sixteen changes of spindle speed, and at least sixteen different feeds are available, while some sizes have as many as twenty feeds. Their range varies slightly in the different sizes of machines, but is such in every case that the correct combination can be had for any cutter that is used.
Power. A milling machine must have ample power, or its use is exceedingly limited. ”

“ Whenever possible, the job should be set up so that the end mill will cut on the lower side of the blank, as this brings the mill and table nearer together and makes the job more rigid. It also prevents chips from accumulating, and enables the operator to better see any lines that may be laid out on the face of the cam.
When the lead of the machine is over 2 inches the automatic feed can be used, but when the lead is less than 2 inches the job should be fed by hand, with the index crank, as shown on page 187. ”

“ 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. ”

“ The shorter distance the mill has to travel, the time saved in shifting feeds, and the fact that the operator does not have to give his undivided attention to the job, are all important advantages.
The metal is 1/2" thick. By the usual method, it is difficult to secure the flat, oil-tight surface that is easily obtained in the way described above.
Milling Grooves in Rim of Pulley on the No. 3 Vertical Spindle Milling Machine
Here a vertical spindle machine equipped with a circular milling attachment is shown milling belt grooves in the rim of a three step pulley. ”

“ 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. ”

“ As a .196" lead is much less than .67", which is the shortest lead [1] regularly obtainable on the milling machine, (see Table of Leads, pages 229 to 247) , the change gears that will give a lead of .67" may be used, and then the angle of the head can be adjusted so that a lead of .196" will be obtained on the cam lobe with these change gears. The rule for this is:
Divide the given lead of the cam lobe by a lead obtainable on the machine, and the result is the sine of the angle at which to set the head. ”

“ It is very essential, therefore, that work be clamped solidly, but in such a manner that it is not sprung. An assortment of clamps or straps, together with jacks, a shim, step block and clamping bolt, are shown on the opposite page. These accessories form an important part of the equipment of a milling machine, and are needed where a variety of work is done. Several sets of each style of strap, and different sizes of step blocks and clamping bolts should always be at hand for use on work of varied shapes. ”

“ When the cone method of drive is employed for vertical spindle milling machines, the belt usually leads from the cone pulley on the countershaft to one on a shaft at the back of the machine. Power is transmitted thence to the spindle on the lighter machines, by means of a quarter-turn belt. ”

“ The only part of the milling machine on which dependence must be placed for accuracy is the hole in the spindle, and this is less liable to get out of truth, from wear such as would impair the accuracy, than are the knee, table, or micrometer screws. The only moving part is the sector, and this, being light, is very sensitive. ”

“ 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. ”

“ 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. ”

“ It is designed for use upon our No. 1 Vertical Spindle Machine, and with it such work as cutting spiral gears, racks, milling keyseats, etc., can be readily done. It is simple in construction and can be quickly attached to the machine.
Circular Milling Attachments. Circular Milling Attachments provide a means of economically doing such work as milling circles, segments of circles, circular slots, etc., on plain and irregular shaped pieces. With the addition of one of these attachments, a vertical spindle milling machine is fully equipped for all varieties of straight
Fig. ”