CHAPTER XIX.

=DRILLS AND CUTTERS FOR DRILLING MACHINES.=

=Jigs or Fixtures= for drilling machines 439 Limits of error in 439 Examples of, for simple work, as for links, &c. 440 Considerations in designing 440 For drilling engine cylinders 440 to 441 For cutting out steam ports 441 =Drills and Cutters= for drilling machines 442 Table of sizes of twist drills, and their shanks 442 Flat drills for drilling machines 442 Errors in grinding flat drills 443 The tit-drill 443 The lip drill 443 Cotter or keyway drills 446 =Drilling holes= true to location with flat drills 444 Drilling hard metal 444 Table of sizes of tapping holes 445 =Drill Shanks= and sockets 445 Improved form of drill shank 446 Square shanked drills and their disadvantages 446 =Drill Chucks= 446 =Stocks and Cutters= for drilling machines 447 Tube plate cutters 448 =Stocks and Cutters.= Adjustable stock and cutter 448 Facing tool with reamer pin 449 Counterbores for drilling machines 449 Drill and counterbore for wood work 449 Facing and countersink cutters 449 Device for drilling square holes 450 Device for drilling taper holes in a drilling machine 451