The mechanic's tool bookWith practical rules and suggestions for use of machinists, iron-workers and others . of such holes, but un-less some extraordinary circumstance demands it,this method will not be used or tolerated by aworkman who calls himself a good mechanic. Asthe drill has no central steadying point on whichto revolve, it cuts in uncertain circles, and as itremoves the metal it chatters and trembles, andwhen it has completed its work the result is apolygonal aperture of which even a raw apprenticeought to be ashamed. A very good tool for enlarging holes is the onehere represented, w
The mechanic's tool bookWith practical rules and suggestions for use of machinists, iron-workers and others . of such holes, but un-less some extraordinary circumstance demands it,this method will not be used or tolerated by aworkman who calls himself a good mechanic. Asthe drill has no central steadying point on whichto revolve, it cuts in uncertain circles, and as itremoves the metal it chatters and trembles, andwhen it has completed its work the result is apolygonal aperture of which even a raw apprenticeought to be ashamed. A very good tool for enlarging holes is the onehere represented, which is termed a counter-bore, or pin drill, or, as it is called in someshops, a sweep. The tool is fitted to the chuckin the same way as the drill and is held in likemanner by the shank ; the opposite or cutting endis flattened and turned to a diameter exactly ofthe size of the hole required. This flat portionmay extend up for two inches or more toward the BORING TOOLS. 117 shank. At the end where the tool enters themetal a tip or pin is made, which must beturned of the same size as the existing hole it. Fig. 27. must enter. The cutting lips, <?, c, of the tool aresloped back with a file so as to form a cuttingedge, of about 60°. On the advancing edge orside, a recess, 0, is hollowed with a small roundfile so as to give the cutting lip more of the formof a cutting tool. The end of the tip is serratedor cut with teeth, so that if the tip should bind inthe hole as the work progresses, their serratededge will cut away the metal which would other-wise bind, and it will be permitted to pass easilyand free through the metal. A set of these toolsought to be as much of a standard as reamers andmade of similar standard sizes. In a dozen ofthese tools made of as many different diameters,there need be only about three sizes of tip, so thatthat number of twist drills will form a hole readyand accurate to receive the tip. One word of caution to the mechanic. The hole in which the tipis
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Keywords: ., bookcentury1800, bookdecade1860, bookpublishernewyo, bookyear1868
