CHAPTER XXI.

=THREAD-CUTTING MACHINERY AND BROACHING PRESS.=

=Pipe Threading=, die stock for, by hand 463 Die stock for, by power 463 Pipe threading machines, general construction of 463 =Bolt Threading= hand machine 464 With revolving head 465 Power threading machine 465 With automatic stop motion 466 Construction of the head 466 Construction of the chasers 466 Bolt threading machine with back gear 467 Single rapid bolt threading machine 467 Double rapid bolt threading machine 467 Construction of the heads of the rapid machines 468 Bolt threading machinery, the Acme 468 Construction of the head of 468 to 470 Capacity of 470 =Cutting Edges= for taps, the number of 471 Examples when three and when four cutting edges are used, and the results upon bolts that are not round 471, 472 Demonstration that four cutting edges are correct for bar iron 472 =Positions of Dies=, or chasers in the heads of bolt cutting machine 473 =Dies=, methods of hobbing, to avoid undue friction 473 The construction of, for bolt threading machines 473 Method of avoiding friction in thread cutting 474 Hob for threading 474 Cutting speeds for threading 474 =Nut Tapping= machine 475 Automatic socket for 475 Rotary 475 Three-spindle 475 =Pipe Threading Machine= 475 to 477 =Tapping Machine= for steam pipe fittings 478 =Broaching Press= 478 Principles of broaching 478 Examples in the construction of broaches 479

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