Production milling

Recent years have witnessed the introduction of many improved methods of performing milling operations. On production work, where high rates of output are essential, this result has been accomplished in various ways, although mainly by a reduction of the nonproductive time of the men and machines in the milling department. In the preparation of this treatise, the author's object has been the same as that of a member of the planning department in a factory, who is called upon to devise methods of milling and to design fixtures that will enable repetition operations to be economically performed. Information and illustrations relating to the latest developments in production milling practice have been gathered by personal studies of the methods used in many of the most progressive manufacturing plants; and an acknowledgement is made to the large number of factory executives who have cooperated in carrying on this work. All of the methods discussed have been successfully used under actual shop conditions.

It has been assumed that all mechanics reading this book are familiar with the various types of production milling machines. For that reason, only brief descriptions of the essential features of each type of milling machine have been included. It is the purpose of this book to explain the application of some of the more efficient methods of operating milling machines on repetition work, rather than to discuss milling machine design. In connection with the examples of machining operations performed on the various types of milling machines, information is included covering the speed and feed at which each operation is performed and the rate of production that is obtained. In a great majority of these cases, the stated output is close to what would appear to be the maximum possible production for the job; therefore, these data should prove of value to other manufacturers handling similar work, in checking up their results with a view to comparing them with those secured by others. No attempt has been made to deal with work holding fixture design, beyond explaining certain fundamental principles which must be observed to keep the ratio of "loading time" to "cutting time" down to a point where a satisfactory output can be secured.

Milling machines are employed for performing a great variety of machining operations. Their range of application extends from the most delicate kinds of precision work done in the tool-room to the heavy-duty work of rapidly removing excess stock from heavy castings and forgings. It is obvious that there must be substantial differences in the designs of milling machines used for such a wide variety of work, as well as in the methods used for equipping and operating them for different classes of milling operations. As implied by the title, this treatise will deal with the subject of production milling and contains, therefore, an explanation of the latest practice in tooling and operating those types of machines that find successful application in the quantity production of duplicate parts. No space will be devoted to the discussion of tool-room work or to an explanation of the methods of performing milling operations where only one piece of work is set up on the machine at a time.

Factors that Increase Rates of Production - Two of the most important factors to consider in the performance of any machining operation, including milling, where a high rate of output is essential, are first, to make sure that the work is done under conditions which closely approximate the maximum rates of speed and feed suitable for the particular case under consideration, and second, to plan the method of operation so that the idle time for both the machine and its operator is reduced to a minimum. There are various commonly used methods of obtaining these results, but one of the most successful in the case of production milling is to employ a type of machine and a method of designing the work-holding fixtures which will enable a number of pieces of work to be set up so that they can all be milled by a single cut. The subsequent discussion will include detailed descriptions of the way in which this principle has been applied to specific milling operations; but as a general statement it may be said that the setting up of a number of pieces of work simultaneously will increase the rates of production by enabling the operator to unload finished pieces while the milling operation is being performed on other pieces of work. This not only reduces the idle time of the operator by keeping him constantly employed, but it also reduces the idle machine time, because the operator usually has had time to remove most of the milled work from the fixture when the last piece is completed.

General Types of Production Milling Machines - Milling machines which find the most general application in American manufacturing plants may be roughly divided into three general classes as follows:

1. Automatic milling machines.
2. Continuous rotary milling machines.
3. Straight-line feed milling machines.

Each of these general classes may be further subdivided, so that milling machines may be classified under the following headings:

1. Automatic millers with straight-line feed movement.
2. Automatic millers with circular feed movement.
3. Automatic millers of the turret type.
4. Continuous rotary millers with the table rotating in a horizontal plane.
5. Continuous rotary millers with the table rotating in a vertical plane.
6. Standard millers with special rotary fixtures.
7. Planer-type millers.
8. Lincoln-type millers.
9. Knee-type millers with multiple fixtures.


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