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QUICK FACT GUIDES FOR MACHINISTS
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GUIDES
FUNDAMENTALS OF
DRILLING & TAPPING
FUNDAMENTALS
OF THREADING ON A LATHE
FUNDAMENTALS OF
WORKING BETWEEN CENTERS FUNDAMENTALS OF HEAT TREATING
FUNDAMENTALS
OF MILLING
FUNDAMENTALS
OF SAWING
METALWORKING
SHOP TERMS
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FUNDAMENTALS
OF DRILLING DRILLING
IS A GROUP OF PROCESSES Hole production is unquestionably the most common of all machining operations, and drilling, itself more a group of processes than a single method, is the most widely used technique for producing holes. Basically categorized by the types of tools they employ, the individual drilling processes possess overlapping capabilities, yet each is unsurpassed in certain areas of application. Choice of the specific process for any particular application starts with the requirements of the hole, diameter, depth, various tolerances, and then must include consideration of production volume and the specific types of drilling equipment available. For the purpose of this guide, we will define drilling basically as the production of holes in solid material by the conversion of the material within that desired cavity into conventional chips by the relative rotation of a cutting tool and the workpiece. Either the tool or the workpiece, in some cases, both, may rotate. There are other methods for making initial holes, including punching of relatively thin stock, coring of a casting, electrical-discharge machining and other electrochemical machining processed, flame cutting, and even zapping the workpiece with a laser or electron beam. These processes, however, are beyond the scope of this guide. Drilling, in many cases, is but the first machining operation in the total production of a hole. Subsequent operations are often required to give that hole its required functional characteristics, such as improved precision of size, location, or cylindricity; finer finish; or special internal configurations exemplified by tapers, threads, keyways, recesses, etc. Typical of these secondary operations are reaming, boring, honing or lapping, counterboring or countersinking, tapping, and broaching. Such processes are also beyond the scope of this guide. As noted initially, the term drilling covers a variety of machining processes, each of which provides special attributes or advantages in the production of certain varieties of holes. One difficulty that all drilling tools share, however, is that they must perform under extremely severe machining conditions. They are buried in the work in an environment that obstructs both coolant flow to the cutting site and the chip flow away from it and that tends to retain heat in both the workpiece and the cutting tool. Except for trepanning the depth of cut is essentially fixed by the radius of the hole being drilled, and (with the same exception) cutting speed varies from an inefficient zero at the center of the hole to whatever maximum has been selected at the periphery of the tool. And the minimal rigidity of what is generally a long and slender tool demands, in most cases, that it obtain lateral support from the hole it is producing.
What are the basic types of drilling tools?
By far the most common is helically fluted twist drills. Covering a size range
in which twist drills are most common is the half round drill, one of the
simplest of all cutting tools and one that offers some advantages that many of
today's manufacturing engineers seem to have forgotten. Both of those two types
are used for producing holes of only several thousandths of an inch in diameter,
but, as dimensions shrink further (to 0.001" and less). The flat
"pivot drill" comes into its own. And, as hole sizes grow to 1"
and more, another type of flat drill becomes prominent, the inserted-blade spade
drill.
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Copyright © 2002 QUICK FACT GUIDES FOR MACHINISTS
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