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TECH FRONT


To view an abstract of the paper, see http://www.nature. com/nnano/journal/v10/n2/full/nnano.2014.307.html.


SME Tech Papers:


Learn More & Do More Holemaking a Fundamental, Challenging Process Ages after primitive peoples pounded, bent and heated malleable metals into tools came the evolution of using a tool to pierce a flat metal piece or to remove material from a deep solid—and the process of holemaking was born. “To qualify as a good machinist is to be able to consistently make holes in exactly the right place—exactly to size, straight, and with good finish. … After most of the usual miseries have been experienced, then there comes a time when a hole driller gets involved in what is known as ‘precision holes,’” and there are many factors that have to be heeded to produce quality holes, summarizes SME Technical Paper TP62PUB6. The paper describes some of the general techniques of


making precision holes, such as boring and reaming, and discusses factors that must be considered regardless of how simple making holes might seem. For example, bush- ings guide reamers to locate holes in the correct position, but due to the close fit needed, ample coolant must be provided to the assembly or the reamer will seize in the bushing. As expected, the paper reports good results with carbide bushings and carbide reamers and coolant.


Gundrilling


Another accepted way to make a precision hole is by gun- drilling, which as noted in TP52PUB39 is still used most com- monly by firearms manufacturers (hence its name) but also for oil and gas, engine and plastic injection mold components. By virtue of a single cutting edge (“…basically a one-sided, single- lip boring tool”) and guidepads that burnish the drilled surface, gundrills produce deep, straight, precise holes. “For gundrilling, the start of the hole is the most important issue,” as explained in TP52PUB39. With, for example, a ½" (12.7-mm) diameter rod 20" (51-cm) long with a tool bit on the end, a starting or guiding device is needed—a bushing. “After the cutting edge or the head in the gundrill has passed in the work past the depth of the bushing, then the drill pro- duces its own guide bushing and it is continued indefinitely.” Again, carbide helps produce even better holes. A gundrill tends to break up chips into smaller pieces, aiding their removal but necessitating the need to get rid of


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