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Consolidated Toledo Drill — Tap Troubleshooting

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.

General Suggestions on Tapping a Drilled Hole

Consolidated Toledo Drill - Tap Drill Sizes
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.

1. Tap Breaking

Possible Cause:
• Dull tap • Drilled hole too shallow
• Hole work hardened
• Incorrect tapping drill size
• Incorrect fixture or Holding device
• Insufficient or Incorrect lubricant
• Lack of lubricant, or Use of wrong type
• Misalignment of tap and hole
• Tapping speed too high
• Tap incorrectly ground
• Tap drill too small
• Tap hits bottom of hole
• Machine or Tapping device faulty
• Work hardened material
• Wrong tap selection

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

2. 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.

3. Chips Clogging Flutes

Possible Cause:
• Wrong type of tap
• Insufficient chamfer
• Incorrect cutting face angle
• Rough Flutes
• Flutes improperly reground
• Lack of lubrication, or Use of wrong type

4. Stripped or Chipped Tap Threads

Possible Cause:
• Misalignment
• Careless handling
• Dull Tap
• Tap too Hard
• Wrong application of surface treated taps
• Improper sharpening of tap

5. Torn or Rough Threads

Possible Cause:
• Incorrect cutting face angle (usually too small)
• 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

6. Tap Sticking or Binding

Possible Cause:
• Tap drill too small
• Tap lands too wide
• Incorrect cutting face angle
• Lack of lubricant, or Use of wrong type
• Surface treatment (lubricant) required

7. Excessive Tap Wear

Possible Cause:
• Blunt or incorrectly sharpened tap
• Hole work hardened
• Insufficient or Incorrect lubricant
• Material is abrasive, or Inclusions present. Surface treated tap required
• Misalignment
• Tapping speed too high
• Wrong tap selection

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

8. Cutting Face Breakdown

Possible Cause:
• Incorrect cutting face angle
• Surface treatment required

9. Overheating of Tap

Possible Cause:
• Excessive land width
• Lack of lubricant, or Use of wrong type
• Dull tap
• Excessive flank contact, pitch diameter relief required
• Excessive tapping speeds

10. Poor Finish on Thread in Tapped Part

Possible Cause:
• Chips/ swarf not being cleared properly
• Dull tap
• Incorrect feed rate
• Insufficient number of chamfered threads
• Incorrect face angle, usually too small
• Insufficient or Incorrect lubricant
• Misalignment of tap and work piece
• Pitch diameter relief required
• Tap drill too small
• Tapping device or Machine faulty

11. Excessive Frictional Drag and Power Requirement

Cause:
• Pitch diameter relief required
• Point size on tap too small
• Dull tap
• Incorrect cutting face angle
• Incorrect tapping speed
• Lack of lubricant, or Use of wrong type
• Incorrect or inadequate equipment
• Misalignment