Viking Drill and Tool — Tap Troubleshooting
A tap cuts a thread on the inside surface of a hole, creating a female surface which functions like a nut. The three taps are Bottoming, Plug and Taper taps, the basic types commonly used by most machinists.The most common type of power driven tap is the "spiral point" plug tap, whose cutting edges are angularly displaced relative to the tap centerline.
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 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 and Tap Drill Size Chart
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.
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.
Minimise Tapping Issues
• Use a pitch controlled tapping attachment
• Choose the correct lubricant. (Type 11-UB Ultra S/P™)
• Use correct type of tap and tapping drill size
• Choose the correct speeds and feeds
• Ensure accurate alignment
• Check hardness of materials, especially when changing batches
• Choose the correct lubricant. (Type 11-UB Ultra S/P™)
• Use correct type of tap and tapping drill size
• Choose the correct speeds and feeds
• Ensure accurate alignment
• Check hardness of materials, especially when changing batches
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
Cutting Face Breakdown
Possible Cause:
• Incorrect cutting face angle• Surface treatment required
Cold Welding
Possible Cause:
• Blunt or Incorrectly sharpened tap• Insufficient OR Incorrect lubricant
• Tapping speed too high
• Material too soft
• Wrong material composition
Excessive Frictional Drag and Power Requirement
Possible 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
Excessive Tap Wear
Possible Cause:
• Blunt OR Incorrectly sharpened/blunt tap• 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
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
Tap Breakage
Possible Cause:
• Dull tap • Drilled hole too shallow• Incorrect tapping drill size
• Incorrect fixture or Holding device
• Insufficient OR Incorrect lubricant
• Misalignment of tap and hole
• Machine OR tapping faulty
• Tap incorrectly ground
• Tap drill too small
• Work hardened material
• Wrong type of tap
Correction:
• Increase chamfer length• Reduce tapping speed
• Shorten thread length
• Tapping too deep
• Use spiral pointed taps in through holes
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
Tap Teeth Chipping
Possible Cause:
• Incorrectly sharpened/blunt tap• Tap hits bottomof hole
• Machine OR tapping device faulty
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
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
Overheating of Tap
Possible Cause:
• Dull tap• Excessive land width
• Excessive flank contact, pitch diameter relief required
• Excessive tapping speeds
• Lack of lubricant OR Use of wrong type
Oversize/Bell Mouthed
Possible Cause:
• Incorrect feed rate• Incorrect tapping drill
• Insufficient OR Incorrect lubricant
• Incorrectly ground or Eccentric tap
• Misalignment
• Tapping device OR Machine faulty
• Wrong tap selection
Poor Finish on Thread in Tapped Part
Cause:
• Chips/swarf not being cleared properly• Dull tap
• Insufficient number of chamfered threads
• Incorrect face angle, usually too small
• Insufficient OR Incorrect lubricant
• Misalignment OR Tap and work piece
• Pitch diameter relief required
• Tapping device OR Machine faulty
• Tap drill too small
• Wrong tap selection