tion of this course to shop operation and shop management, especially as applied to structural bridge shops.

Second, I think it not correct to limit our instruction to ordinary statically determined structures. To turn out the best men we must at least give them the underlying principles of statically indeterminate structures.

Third, we have systems of routing material through shops. Why not come thought to a system of routing men through organizations which design, fabricate and erect bridges and other structures?

REPORT OF COMMITTEE NO. 16-MECHANICAL

ENGINEERING.

METHODS OF TEACHING MACHINE DESIGN.

Your committee, which was asked to consider the subject "Methods of Teaching Machine Design," desires to submit the following report:

The courses in machine design, usually required of undergraduates taking a mechanical engineering course, should give the student a thorough training in the fundamental principles involved in the design and operation of machinery. Furthermore, such courses should impart to the student a certain amount of practical knowledge pertaining to the methods used in manufacturing, assembling, operating and repairing machinery of not too complicated a nature. In addition to teaching principles and imparting a certain amount of practical knowledge, the student should be taught how and where to search for additional knowledge to be used in more complicated problems.

In order that such courses be effective, the student must be well grounded in the various shop processes, in mathematics, mechanics and kinematics, in the properties of materials used in the construction of machinery and in the strength of materials. The student must not only be familiar with the principles of mathematics, mechanics, kinematics, etc., but he must have the ability to recognize and apply such principles to the various problems that are presented for solution. In addition to the various subjects just enumerated, courses in machine design presuppose a knowledge of machine drawing and sketching as well as descriptive geometry.

A study of the various methods of teaching machine design in a number of American technical schools seems to indicate that four methods are used. These are as follows:

1. First Method. Students are assigned isolated problems, each one of which is treated independently and has no connection or relation whatsoever with any of the other problems. Some of these problems are frequently of such a nature that they test out the inventive ability possessed by the student. Among the problems commonly met with are the following: Design of riveted joints, pins, key and screw fastenings, shafting and bearings, pulleys and gears of all kinds, couplings and clutches, cams, etc.

2. Second Method. Students working independently or in groups are required to design a certain type of machine or series of machines of the same type, thus bringing out the relation existing between the various elements used in building up a machine. For the reason just stated a considerable number of machine design teachers prefer this method in place of that given in (1) above. These problems may be selected by the individual student or assigned by the instructor. In the majority of cases the machines designed are comparatively simple, containing elements, the design of which involve the use of simple as well as combined stresses. The following machines are or have been used by various teachers: shapers, slotters, toggle-joint presses, punching and shearing machines, hydraulic and pneumatic riveters, cranes, drum hoists, air hoists, drilling machinery, etc.

3. Third Method.-Students are given the drawings of comparatively simple machines, such as are mentioned in (2) above, and then are required to make a complete force and stress analysis of all parts or elements used in the machine. Frequently actual machine parts that have failed in service are examined and analyzed in order to determine the probable cause of failure.

4. Fourth Method. Students are assigned a series of problems some of which are of the type discussed under (1) and (3) and at least one problem is of the type discussed under (2), so that the student may obtain a connected idea of an entire machine and how machines are developed from a series

of simple machine elements. This method embodies the good points of all the other methods previously mentioned and has given very good results in the institutions that are using it.

Statement of Problem.-The manner in which a machine design problem is stated and placed before the student, is a very important matter and should receive considerable thought and attention from the teacher or teachers in charge of the courses. Frequently the statement of the problem is incomplete and as a result the student wastes valuable time before he discovers that some important data or statement has been omitted. A good plan, followed by some teachers, is to work out the problems before they are assigned thus any omission or error may be corrected before the student attempts a solution. This plan requires much of the teacher's time, but the results obtained generally warrant such expenditure of time.

In some institutions, where the problems are of the type discussed under method (2) above, the statement of the problem is in the form of a specification in which the essential data are included. Such specifications should be drawn up very carefully so that they may serve as examples for future. reference. Another way of making problem assignments is to give a brief statement containing the essential data and then require the student to consult the trade literature for additional help, if it is needed. With problems of this nature it is suggested that the student be made to write a complete specification of the machine as it was designed by him.

Requirements of the Problem.-The student's solution of any problem should include the following: (1) A series of sketches, to be submitted to the instructor for approval, in which the student conveys to the instructor some idea of the details that he expects to introduce into his design. (2) An outline giving in detail the method employed in arriving at the proportions of the various elements used in the machine. This outline, the instructor in charge of the course should discuss with the student before approving it. (3) A series of calculations, accompanied by the necessary free-hand sketches,

which should be arranged in a neat and logical manner. Such calculations should be submitted to the instructor at frequent intervals for checking and approval. (4) After the calculations are completed and approved, the student should make a drawing showing the assembly of the machine or of the machine element which he designed. Some institutions merely require a well-made pencil drawing, while others demand both a pencil drawing and a tracing. (5) Having completed the drawing, the student should be required to write out a complete specification of the machine or element of the machine which he designed, unless such a specification formed the statement of the problem. (6) In certain types of problems that are not too complicated it is feasible to require the student to make an estimate of the cost of the machine he designs. This is very desirable, as the student should be given some idea as to the most of machines as well as of the standard parts used in such machines.

In some institutions students are given individual problems while in others, the students work in groups of two or more. With the latter system the best man in the group may be considered as the leader and might then be held responsible for the progress made by the group. The group system has proven highly satisfactory when each group of men was required to design a series of machines, say a series of punching and shearing machines all of which have the same capacity but of different throat depths. It is evident that in such a series of machines there are a considerable number of parts that must be interchangeable, thus compelling the students to coöperate with each other when designing such parts. For example, the ram or slide as well as the back-stand of a series of punching and shearing machines having the same capacity must be designed so that they will fit all of the frames in that series. Furthermore, in order that a double machine may be built, it is necessary that many important dimensions on the various sizes of frames must agree with each other or it is impossible to place two frames back to back.