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Tap Troubleshooting

America´s Finest High–Speed Cutting Tools™

Tapping Machine, Tap Holding Device and the Hole
Problems encountered in tapping are often the fault of the tapping machine, tap holding device 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.

Tap holding device should be checked as to correct type, for wear and alignment with the hole.

Drilled hole should be checked for diameter and trueness in round and axis to assure correct percentage of thread engagement. Blind holes must have sufficient chip room at the bottom.

Tap Breaking
Possible Cause:
• Drilled hole too shallow.
• Hole work hardened.
• Incorrect tapping drill size.
• Incorrect fixture or Holding device.
• Insufficient or Incorrect lubricant.
• Misalignment of tap and hole.
• Tapping speed too high.
• Tap hits bottom of hole.
• Work hardened material.

Correction:
• Increase chamfer length.
• Reduce tapping speed.
• Use spiral pointed taps in through holes.
• Increase chamfer length.

Tap Failure On Reversal
Possible Cause:
• Tap cutting too tightly. Cutting face angle should be increased.
• Tap galling. Face angle on back of land should be increased.
• Chips wedged between flutes.

Correction:
• Increase feed.
• Consider use of chip-breaker design drill and/or chip-breaker point grind.

Chips Clogging Flutes
Possible Cause:
• Wrong type of tap. • Insufficient chamfer. • Incorrect cutting face angle. • Rough flutes. • Lack of lubrication, or use of wrong type.

Stripped or Chipped Tap Threads
Possible Cause:
• Misalignment. • Dull tap. • Tap too hard. • Wrong application of surface treated taps

Torn or Rough Threads
Possible Cause:
• Tap drill to small.
• Chips clogging flutes.
• Broken threads on taps.
• Improper resharpening of tap.
• Lack of lubricant or use of wrong type.

Correction:
• Resharpen or replace.
• Reduce speed.
• Use larger drill.
• Use lubricant.

Tap Sticking or Binding
Possible Cause:
• Tap drill too small. • Tap lands too wide. • Lack of lubricant or use of wrong type. • Surface treatment. (lubricant) required.

Excessive Tap Wear
Possible Cause:
• Hole work hardened.
• Insufficient or incorrect lubricant.
• Material is abrasive or inclusions present. Surface treated tap required.
• Tapping speed too high.
• Wrong tap selection.

Correction:
• Increase chamfer length.
• Reduce tapping speed.
• Ensure adequate lubricant.
• Use larger drill.

Overheating of Tap
Possible Cause:
• Excessive land width. • Lack of lubricant or use of wrong type. • Excessive flank contact, pitch diameter relief required. • Excessive tapping speeds.

 

 


General Suggestions on Tapping a Drilled Hole

1. If holes are "Undersize or oversize" check against the setup instructions. Check the tap for correct Pitch diameter limit for desired "Class of thread", and the "Drill for correct size".

2. If the tap is "Producing rough thread" it generally means the tap is pushing or tearing the metal instead of cutting it. The tap may be dull, have galled threads or may be running at too slow a speed. If none of these, increase the hook angle of the cutting face.

3. If the tap is "Loading (metal clinging to the tap) or Galling" check the lubrication. Here too, the tap may be dull, or it may be producing too high a percentage of thread. Shift to a surface-treated tap.

4. If "Tap breakage" is encountered the tap may be cutting to high a percentage of thread, be insufficiently lubricated or have too little clearance for chips at the bottom of the blind hole.

If none of these conditions exist, Increase the speed, except in hard or tough materials. In these materials, lower the speed.

Drill & Tap Products —

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