Tapping Problems

Friday, 1 September 2023

Tapping problems encountered are often the fault of the tapping machine, tap holding devices and conditions of the hole to be tapped.  The tapping machine should be checked for spindle, fixture and work alignment; for slipping belts, wear and power.  The tap holding device should be checked as to correct type, for wear and alignment with the hole.  The drilled hole should be checked for diameter, trueness in round and axis to assure correct percentage of thread engagement.  Blind holes must have sufficient chip room at the bottom.
Tapping TroublePossible Cause
Chips clogging flutesWrong type of tap, insufficient chamfer, incorrect cutting-face angle, rough flutes, flutes improperly reground, lack of or wrong type of lubrication or insufficient ship space.
Stripped or chipped tap threadMisalignment, careless handling, dull tap, tap too hard, improper application of surface treated taps, improper sharpening of tap.
Torn threads in tapped partIncorrect cutting-face angle (usually too small), tap drill too small, chips clogging flutes, broken threads on taps, improper sharpening of tap, lack of lubrication or wrong type.
Tap sticking or bindingTap drill too small, tap lands too wide, incorrect cutting-face angle, lack of or wrong type of lubrication, surface treatments (lubricant) needed.
Excessive tap wearMaterial is abrasive or inclusions are present (surface treated or premium guide of HSS-E tap required), misalignment or insufficient lubrication.
Cutting-face breakdownIncorrect cutting-face, surface treatment needed.
Overheating of tapExcessive land width, lack of or wrong type of lubrication, dull tap, excessive flank contact (pitch diameter relief required), excessive tapping speed.
Poor finish on thread in tapped partIncorrect cutting-face angle (usually too small), tap drill too small, insufficient number of chamfered threads, dull tap, lack of or wrong type of lubrication.
Excessive frictional drag and power requirementPoint size on tap too large, dull tap, incorrect cutting-face angle, incorrect tapping speed, lack of or wrong type of lubrication, incorrect or inadequate equipment, misalignment.
Tap breakageWrong type of tap, dull tap, tap incorrectly ground, tap drill too small, drilled hole to shallow, misalignment of tap and hole, wrong machine, incorrect fixture or tap holding device, work hardened material, lack of or wrong type of lubrication.
Tap failure on reversalTap cutting to tightly (increase cutting-face angle), tap galling (increase face angle on back of land), chips wedged between the flutes.
Edge ChippingReversing or backing off when using HSGT Taps in hand tapping applications should be avoided as it can cause chipping.  HSGT Taps are designed for machine use primarily and when used as hand taps, should be driven straight through without any backing off.