Cutting tools include nearly all that are employed in finishing; lathes, planing machines, drilling and boring machines, shaping, slotting and milling machines, come within this class. The machines named make up what are called standard tools, such as are essential and are employed in all establishments where general machine manufacture is carried on. Such machines are constructed upon principles substantially the same in all countries, and have settled into a tolerably uniform arrangement of movements and parts.
Besides the machine tools named, there are special machines to be found in most works, machines directed to the performance of certain work; by a particular adaptation such machines are rendered more effective, but they are by such adaptation unfitted for general purposes.
General engineering work cannot consist in the production of duplicate pieces, nor in operations performed constantly in the same manner as in ordinary manufacturing; hence there has been much effort expended in adapting machines to general purposes—machines, which seldom avoid the objections of combination, pointed out in a previous chapter.
The principal improvements and changes in machine fitting at the present time is in the application of special tools. A lathe, a planing machine, or drilling machine as a standard machine, must be adapted to a certain range of work, but it is evident that if such tools were specially arranged for either the largest or the smallest pieces that come within their capacity, more work could be performed in a given time and consequently at less expense. It is also evident that machine tools must be kept constantly at work in order to be profitable, and when there are not sufficient pieces of one kind to occupy a machine, it must be employed on various kinds of work; but whenever there are sufficient pieces of the same size upon which certain processes of a uniform character are to be performed, there is a gain by having machines constructed to conform as nearly as possible to the requirements of special work, and without reference to any other.
It is now proposed to review the standard tools of a fitting shop, noticing the general principles of their construction and especially of their operation; not by drawings nor descriptions to show what a lathe or a planing machine is, nor how some particular engineer has constructed such tools, but upon the plan explained in the introduction, presuming the reader to be familiar with the names and purposes of standard machine tools. If he has not learned this much, and does not understand the names and general objects of the several operations carried on in a fitting shop, he should proceed to acquaint himself thus far before troubling himself with books of any kind.
(1.) Why cannot the parts of machinery be made to accurate dimensions by forging or casting?—(2.) What is the difference between hand tool and machine tool operation as to truth?—(3.) Why cannot hand-work be employed in duplicating the parts of machinery?—(4.) What is the difference between standard and special machine tools?
CHAPTER XXX.
TURNING LATHES.
In machinery the ruling form is cylindrical; in structures other than machinery, those which do not involve motion, the ruling form is rectangular.
Machine motion is mainly rotary; and as rotary motion is accomplished by cylindrical parts such as shafts, bearings, pulleys and wheels, we find that the greater share of machine tools are directed to preparing cylindrical forms. If we note the area of the turned, bored and drilled surface in ordinary machinery, and compare with the amount of planed surface, we will find the former not less than as two to one in the finer class of machinery, and as three to one in the coarser class; from this may be estimated approximately the proportion of tools required for operating on cylindrical surfaces and plane surfaces; assuming the cutting tools to have the same capacity in the two cases, the proportion will be as three to one. This difference between the number of machines required for cylindrical and plane surfaces is farther increased, when we consider that tools act continually on cylindrical surfaces and intermittently on plane surfaces.