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Tapping Troubleshooting

Tapping is a machining technique that creates threads on internal surfaces. Taps are cylindrical or conical thread-cutting tools with threads of the desired form around their circumference - the tap cuts or forms internal threads by combining rotary motion and axial motion.

Tapping operations are one of the last steps before completion, and they are the most prone to errors since they require careful planning, balance, and research. If several scrapped parts have an error, it could waste a great deal of time.

Factors To Consider Before Tapping

Due to lack of sensory connection during tapping operation, particularly when using CNC machines, it may be challenging to detect malfunctions until it is too late to be corrected. For a successful tapping process, it is important to consider the following issues:

  • How hard is the metal workpiece material?
  • Are the screw holes deep, or is the workpiece thick?
  • What type of screw hole is processed? A through-hole or blind hole?
  • The workpiece to be processed consists of what kind of material? Is it steel, cast iron, or hardened steel?
  • What is the threaded hole size and type?

If these concerns are not addressed, thread taps may have various problems, including chipping of teeth, breaking, excessive wear, large or undersized pitch diameters, and rough surfaces. 

Problems and Solutions Related to Tapping

The following analyzes likely causes and remedies when tapping threads in metal. By applying them during tapping, you minimize the occurrence of issues.

  • Rapid Wear
  • Possible Cause


    • Tape that is not suitable for the application
    • Incorrect surface treatment
    • Incorrect or inadequate lubrication
    • A tap speed that is too fast
    • Drilled hole hardening
    • Insufficient drill hole size
    • Application of wear-resistant surface treatments is recommended
    • Choose an emulsion or oil that is appropriate
    • Reduce the cutting speed and check drilling recommendations
  • Oversized Thread
  • Possible Cause


    • There is an incorrect tolerance
    • Tap on the incorrect application
    • A wrong axial feed has been detected
    • There is too much lag in the tap speed
    • A thread overfed on a faulty tool holder
    • Choose a tap with a lower tolerance
    • Recheck the application charts
    • Maintain a controlled feed rate
  • Undersized Thread
  • Possible Cause


    • The wrong tolerance level
    • The tap is worn out
    • Pull off the excessive pressure
    • Insufficient drill hole size
    • After tapping, the material closes in
    • Select a tap with a higher tolerance
    • Replacing
    • Tap attachments should be adjusted
    • Increase the diameter of the drill
  • Built-Up Edge (BUE)
  • Possible Cause


    • Incorrect tap type for the application
    • The tap is worn out
    • No lubricant or insufficient lubrication
    • Replacing
    • Use emulsions or oils that are appropriate
  • Breakage During Retraction
  • Possible Cause


    • Torque is too high
    • The tap is worn out
    • Lubrication that is incorrect or inadequate
    • The bottom of the hole is hit with a tap
    • Tap speed is too fast
    • The chip is trapped
    • Insufficient drill hole size
    • Tap holders with torque settings should be used
    • Replacing
    • Use emulsions or oils that are appropriate
    • Reduce thread depth or increase drill depth
    • Cutting at a lower speed
    • Check the tool selection
  • The Surface Roughness of the Internal Thread Is Too High
  • Possible Cause


    • An incorrect tap type is selected
    • Cutting at too high a speed
    • Insufficient length of the cutting cone
    • It is difficult to remove chips smoothly
    • Oversize internal diameter of the bottom hole 
    • Having a cool condition
    • Select the correct tap based on the processing conditions
    • Slow down the cutting speed
    • Extend the length of the cutting cone
    • Select the correct tap based on the processing conditions
    • Based on the corresponding standard, choose the diameter of the bottom hole
    • Enhance cooling and lubrication
  • Tapping Bell Mouthed Hole
  • Possible Cause


    • Incorrect initial starting pressure
    • A hard-working axial spindle
    • Fixture positioning or fixturing incorrectly
    • Working with a controlled tap feed
    • Using tap stands with adjustable lengths are ideal
    • Select the appropriate tap tolerance
  • Torn Thread
  • Possible Cause


    • The face is angled incorrectly (usually too small).
    • The tap drill is too small 
    • Flute clogged by chips 
    • Taps with broken threads 
    • Tap resharpening is done incorrectly
    • Lubrication is inadequate or incorrect
    • The face angle should be adjusted and increased
    • Increase size if necessary
    • Reverse the tap slowly to break chips and check your lubricant
    • In this case, the hole is too small, so increase the tap size
    • Re-sharpen or replace the tap
    • Re-adjust


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