Fifth, all persons who use the gauges should be carefully instructed and trained in their use. A gauge is an expensive and comparatively delicate instrument, and a careless operator can spoil one on the first piece he gauges; or a foreman with one in his drawer can ruin it by knocking around or mishandling. The final inspectors should set the standard of handling and use, and instruct all others as far as pos sible to use them likewise.
Work must be held to slightly closer toler ances than the maximum allowable, since it is impossible to work to a maximum without sometimes exceeding it; so the operator has the gauges allowing the smallest working toler ances, as his normally receive the greatest amount of wear.
The Specifications.— Only on very simple or familiar mechanisms do the drawings, gauges, etc., give sufficient information for in telligent manufacture. Specifications should form an integral part of the equipment. As said above, they should explain clearly and definitely the requirements and desired results, character and composition of materials, the chief functioning points and sizes, class of workmanship demanded, and any unusual manufacturing methods required; with the character and method of inspection. In fact, any information of value in the process should find here a permanent record. If any require-, ments are unimportant, and economy is the main factor, that fact should be stated also. These specifications may be incorporated on the drawings, if desirable and they are simple; otherwise be kept as an independent record, and revised to keep abreast of current practice. They are as yet a rarity in general establish ments, but their value and help are becoming more widely acknowledged. The best examples are in government supplies, as munitions.
The Manufacturing Equipment consists of the tools, jigs, fixtures and machines re quired. A jig or fixture is a device for holding a piece in proper position while some machin ing operation is performed upon it. Each oper ation usually needs a special jig. Its general type or design depends entirely upon the part to be wrought. One factor, however, remains constant, and must always be kept in mind for satisfactory results; the locating points for any operation should always be those from which the machined surface is dimensioned. A strict observanceof this fundamental principle will eliminate many manufacturing difficulties.
If a model has been suitably developed, many size blocks, master plates and other valuable accessories will be available, that will not only ensure greater accuracy in the equip ment and a corresponding uniformity in the product, but greatly decreased expense in equip ment costs. In any event, if a model is avail able, all equipment should be carefully tested to it before being forwarded to the production departments.
The Production, a general mechanical busi ness, need not be dealt with here; the next step is The This department has the responsibility, and should have the power, of maintaining the standards of accuracy and It should be entirely independent of the production department, whose duties are in compatible with its own, and too often held and performed as hostile. It must be provided with all needful testing and checking apparatus; and its duty is to see that all work is up to the mark before passing from machine to machine, or department to department. Its detailed duties depend upon the nature of the product; but in any case its personnel should be individuals of good judgment, intimately acquainted with the requirements, and well trained in the use of the testing facilities.
The Assembling furnishes final proof whether due attention has been paid to the factors of size; unhappily, the test for quality of material mostly lies in use, and detection of neglect comes too late. If the parts may be as sembled without fitting or further machining, and the mechanism performs its functions properly, it is conclusive evidence that the dimensions have been kept true. On the other hand, if fitting or other modifications are neces sary, it is equally conclusive proof that some vital factor has been overlooked, and investiga tion to locate and correct the trouble should follow. In truly interchangeable work, no machining will be performed in the assembling room.
Interchangeable manufacturing requires many types of skilled workmen. As operations are simplified, the needed skill becomes less; but a corresponding increase is required in preparation work and supervision. The basic principles remain fixed, but their application must be modified to suit particular factors of product, class of equipment available and type of workmen employed.