CHAPTER XI.

=DRILLING AND BORING IN THE LATHE.=

=The Twist Drill= 274 Twist drill holders 274 The diametral clearance of twist drills 274 The front rake of twist drills 275 The variable clearance on twist drills as usually ground 275 Demonstration of the common error in grinding twist drills 276 The effects of improper grinding upon twist drills 276 Table of speeds and feeds for twist drills 277 Grinding twist drills by hand 279 Twist drills for wood work 279 =Tailstock Chucks= for drilled work 279 =Flat Drills= for lathe work 280 Holders for lathe work 281 =Half-round= bit or pod auger 281 With front rake for wrought iron or steel 281 With adjustable cutter 281 For very true work 281 =Chucking Reamer= 281 The number of teeth for reamers 282 Spacing the teeth of reamers 282 Spiral teeth for reamers 282 Grinding the teeth of reamers 282 Various positions of emery-wheel in grinding reamers 282 Chucking reamers for true work 283 Shell reamers 283 Arbor for shell reamers 283 Rose-bit or rose reamers 283 Shell rose reamers 284 Adjustable reamers 284 Stepped reamers for taper work 285 Half-round reamers 285 Reamers for rifle barrels 285 =Boring Tools= for lathe work 285 Countersinks 285 Shapes of lathe boring tools 285 Boring tools for brass work 286 The spring of boring tools 286 Boring tools for small work 287 Boring tool holders 287 =Boring Devices for Lathes= 288 =Boring Heads= 288 =Boring Bars= 289 Boring bar cutters 289 Three _versus_ four cutters for boring bars 290 Boring bars with fixed heads 290 With sliding heads 290 Bar cutters, the shapes of 291 Boring head with nut feed 291 Boring bars for taper work, various forms of 292 Boring double-coned work 293 Boring bar, centres for 293 =Cutting Speeds= and feeds for wrought iron 294 Examples of speeds taken from practice 295