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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,thermosettingnickel base alloy,
troublelow carbon steelmiddle carbon steelhigh carbon steel, heat treated steel of lower than 35HRCstainless steelcast iron, tough cast ironaluminum alloy, zinc alloy, brassresin, thermoplastic resintitanium alloy, heat treated steel of lower than 35HRC
tap wear, cutting performance 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-machine material
  • Trouble shooting
trouble check pointOver-cutting of internal threadsShrinkage of internal threadsRough surface, Torn threadsStop linetap wear, cutting performance decreasedwelding on tapchipping on tapchip clogging
Used 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
Adjust properly thestroke of tapping
Cutting conditionReduce cutting speed, Adjust a feedReduce cutting speedReduce cutting speed
LubricantChange to insoluble oil other cutting oil whichfrom water soluble, Use prevents cold weldingChange to insoluble oil other cutting oil when pfrom water soluble, Use revents cold weldingAdjust 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 t tapl ap, Use interrupted
Tap DesignReconsider 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： PT1/4-19size： PT1/4-19
tap： Straight flute taptap： Straight flute tap
material ： SS400milling
cutter： 08153X19G
machine ： Machining center
holder： fixed typematerial： SS400
lubricant ： water solubleTapping speed: 5m/minTapping speed: 2.5m/minmachine ： Machining centerStraight flute tapThread milling cutter
Torn threadsNo torn threadsholder： fixedThere is the stop lineThere is no stop line

lubricant ： water soluble Technical Inf