Tap Troubleshooting
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. 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 and trueness in round and axis to assure correct percentage of thread engagement. Blind holes must have sufficient chip room at the bottom.

General Suggestions
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.

Trouble and Cause:
· Tap Breakage
1. Wrong type of tap.
2. Dull tap.
3. Tap incorrectly ground.
4. Tap drill too small.
5. Drilled hole too shallow.
6. Misalignment of tap and hole.
7. Wrong machine.
8. Incorrect fixture or holding device.
9. Work hardened material.
10. Lack of lubricant, or use of wrong type.

·Tap Failure on reversal
1. Tap cutting too tightly. Cutting face angle should be increased.
2. Tap galling. Face angle on back of land should be increased.
3. Chips wedged between flutes. (See the following)

· Chips Clogging Flutes
1. Wrong type of tap.
2. Insufficient chamfer.
3. Incorrect cutting face angle.
4. Rough Flutes.
5. Flutes improperly reground.
6. Lack of lubrication, or use of wrong type.

· Stripped or Chipped Tap Threads
1. Misalignment.
2. Careless handling.
3. Dull Tap.
4. Tap too hard.
5. Wrong application of surface treated taps.
6. Improper sharpening of tap.

· Torn Threads in Tapped Part
1. Incorrect cutting face angle (usually too small).
2. Tap drill to small.
3. Chips clogging flutes.
4. Broken threads on taps.
5. Improper resharpening of tap.
6. Lack of lubricant, or use of wrong type.

· Tap Sticking or Binding
1. Tap drill too small.
2. Tap lands too wide.
3. Incorrect cutting face angle.
4. Lack of lubricant, or use of wrong type.
5. Surface treatment (lubricant) required.

· Excessive Tap Wear
1. Material is abrasive, or inclusions present. Surface treated tap required.
2. Misalignment.

· Cutting Face Breakdown
1. Incorrect cutting face angle.
2. Surface treatment required.

· Overheating of Tap
1. Excessive land width.
2. Lack of lubricant, or use of wrong type.
3. Dull tap.
4. Excessive flank contact, pitch diameter relief required.
5. Excessive tapping speeds.

· Poor Finish on Thread in Tapped Part
1. Pitch diameter relief required.
2. Incorrect face angle, usually too small.
3. Tap drill too small.
4. Insufficient number of chamfered threads.
5. Dull tap.
6. Lack of lubricant, or use of wrong type.

· Excessive Frictional Drag and Power Requirement
1. Pitch diameter relief required.
2. Point size on tap too small.
3. Dull tap.
4. Incorrect cutting face angle.
5. Incorrect tapping speed or misalignment
6. Lack of lubricant, or use of wrong type.
7. Incorrect or inadequate equipment.