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3. Troubles on taper pipe thread tapping, and their solution

Taper pipe thread tapping such as for PT thread and for NPT thread is quite different from parallel thread tapping such as for metric thread. There, the trouble particularly special in taper thread tapping tends to happen. Following is the explanation about tapping troubles on taper pipe thread tapping and their solution:

  • Materials and troubles
materialtool steel, alloy steel,nickel base alloy,
troublelow carbon steelmiddle carbon steelhigh carbon steel, heat treated steel of lower than 35HRCstainless steelcast iron, tough cas iront aluminum alloy, zinc alloy, brassthermosetting resin, thermoplastic resintitanium alloy, heat treated steel of lower than 35HRC
tap wear, cutting performace decreased▲●▲●ー
welding on tap●●▲●●ー
chipping on tap▲▲●●ー
rough surface▲▲▲▲●▲▲ー
torn threads●●▲●▲ー
chip clogging●●▲ー
  • Trouble occurs quite frequently ▲ Trouble occurs rather frequently ー Hard-to-macine material
  • Trouble shooting
check pointtroubleOver-cutting of intenal threadsShrinkage of interna threadsl Rough surface, Torn threadsStop linetap wear, cutting performace decreasedwelding on tapchipping on tapchip clogging
MachineSelect machine suitable for tapping sizeUse machine with more powerUse machine with more power
Jigs, HoldersFix workpiece firmlyUse tap holder of floating type, Prevent vibrating of axis of tap, Prevent centering- off with workpiece
Cutting conditionAdjust properly the Reduce cutting speed, Adjust a feedstroke of tappingReduce cutting speedReduce cutting speed
LubricantChange to insolubl soluble, Use other c prevents cold welde oil from water utting oil which ingChange to insoluble soluble, Use other c prevents cold weldioil from water utting oil when ngAdjust oil volume,supply oil properly
On processPrevent slanting of holeUse taper reamer for boring holeProvide deeper tapping hole, Remove unnecessary chips during tappingProvide deeper tapping hole, Check the viscosity, Use taper reamer for boring hole
SelectionUse spiral fluted tap, Use interrupted tapUse thread mill cuttersUse carbide tap (depending on materials being cut)Use interrupted tapsUse spiral fluted ta tapl p, Use interrupted
TapDesignReconsider of number of flutes of tapChange material of tapProvide oxide surface treatment, Provide TiN or TiCN on taps, Provide larger cutting angleSelect long shank tap when ejecting chips interferes with tap holder in the case of SP tapping
  • Examples of trouble shooting

1) Torn thread trouble was solved by changing cutting speed 2) Stop line trouble was solved by using Thread milling cutter Tapping condition Cutting condition

size： PT 1/4-19size： PT1/4-19
tap： Straight flute taptap： Straight flute tap
material： Low carbon steelmilling
  • 08153X19G

machine Machining center cutter

  • material
  • Low carbon steel

holder fixed type

  • machine
  • Machining center
lubricantwater solubleTapping speed: 5m/minTapping speed: 2m/minStraight flute tapThread milling cutter
Torn threadsNo torn threadsholder： fixedThere is the stop lineThere is no stop line

lubricant water soluble