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6 Common Thread Tap Problems and Solutions When Tapping Threads

Tapping metal threads is a more difficult processing process because its cutting edge is 100% in contact with the metal workpiece. To avoid various problems with the thread taps during the tapping process, the following issues should be considered before tapping:

  • What material is the workpiece to be processed? Steel, cast iron, or hardened steel?
  • What is the hardness of the metal workpiece material?
  • Is the processed screw hole a through-hole or a blind hole?
  • How deep is the screw hole (or what is the thickness of the workpiece?)
  • What is the type and size of the threaded hole to be processed?

Once these issues are not appropriately considered, the thread tap may have a series of problems, such as the thread tap break off, tooth chipping, excessive wear, large or small pitch diameter, and too rough surface.

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Below we will analyze the possible causes and solutions of these problems when tapping threads in metal one by one.

The common problem 1: The thread tap is broken

Common cause

  • The diameter of the threaded bottom hole is too small during tapping internal thread processing, and the chip removal is not good, causing thread tap chip blockage;
  • When the thread cannot be tapped, the drilling depth is not enough;
  • The cutting speed is too high and too fast when tapping the thread;
  • The thread tap used for tapping and the threaded bottom hole have different diameters;
  • The selection of tap sharpening parameters is inappropriate, and the hardness of the workpiece is unstable;
  • The thread tap has been used for a long time and is excessively worn.

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Solution:

  • Correctly select the diameter of the threaded bottom hole;
  • The inclination of sharpening the blade or the use of spiral flute taps;
  • The depth of the bottom hole must meet the specified standard;
  • Appropriately reduce the cutting speed and select according to the standard;
  • When tapping thread, correct the tap and the bottom hole to ensure that it coaxially meets the requirements, and use a floating tapping chuck;
  • Increase the rake angle of the tap and shorten the length of the cutting cone;
  • Ensure that the hardness of the workpiece meets the requirements, and choose a safety chuck;
  • If the tap is found to be worn out, it should be replaced in time.

The common problem 2: thread Tap teeth are broken

Common reasons:

  • The rake angle of the thread tap is too large;
  • The cutting thickness of each tooth of the tap is too large;
  • The quenching hardness of the tap is too high;
  • The tap has been used for a long time and is severely worn.

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Solution:

  • Appropriately reduce the rake angle of the thread tap;
  • Appropriately increase the length of the cutting cone;
  • Reduce the hardness and replace the taps in time.

The common problem 3: The thread tap wears out too fast

Common cause

  • The cutting speed is too high when tapping threads;
  • The selection of tap sharpening parameters is inappropriate;
  • Improper selection of cutting fluid and insufficient cutting fluid;
  • The material hardness of the workpiece is too high;
  • When the tap is sharpened, burns occur.

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Solution:

  • Appropriately reduce the cutting speed;
  • Reduce the rake angle of the tap and lengthen the length of the cutting cone;
  • Choose cutting fluid with good lubricity;
  • Appropriate heat treatment of the processed parts;
  •  Sharpen the taps correctly.

The common problem 4: The pitch diameter of the thread is too large:

Common reasons:

  • Improper selection of the pitch diameter accuracy grade of the thread tap;
  • Unreasonable cutting selection;
  • Tapping thread cutting speed is too high;
  • The coaxiality of the tap and the threaded bottom hole of the workpiece is poor;
  • The parameter selection of tap sharpening is inappropriate;
  • Burrs are produced in the sharpening tap, and the length of the tap cutting cone is too short.

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Solution:

  • Choose the pitch diameter of the tap with a reasonable accuracy level;
  • Choose a suitable cutting fluid and appropriately reduce the cutting speed;
  • When tapping the thread, correct the coaxiality of the tap and the bottom hole of the thread, and use a floating chuck;
  • Appropriately reduce the rake angle and the cutting cone back angle;
  • Remove the burrs produced by the sharpening tap and adequately increase the length of the cutting taper.

The common problem 5: The pitch diameter of the thread is too small:

Common reasons:

  • Improper selection of the pitch diameter accuracy grade of the tap;
  • The choice of tap sharpening parameters is unreasonable, and the tap is worn;
  • The cutting fluid selection is inappropriate.

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Solution:

  • Choose the pitch diameter of the tap with the appropriate accuracy level;
  • Appropriately increase the rake angle and cutting cone angle of the tap;
  • Replace the excessively worn taps;
  • Choose cutting fluid with good lubricity.

The common problem 6: The thread surface roughness value is too large:

Common reasons:

  • The selection of tap sharpening parameters is inappropriate;
  • The hardness of the workpiece material is too low;
  • The tap sharpening quality is not good;
  • The cutting fluid selection is unreasonable;
  • The cutting speed is too high when tapping the thread;
  • The tap is worn for a long time.

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Solution:

  • Appropriately increase the rake angle of the tap and reduce the cutting cone angle;
  • Carry out a heat treatment to appropriately increase the workpiece's hardness to ensure that the tap's rake face has a lower surface roughness value. Choose a cutting fluid with good lubricity;
  • Appropriately reduce the cutting speed;
  • Replace worn taps.

The above are some of the problems that may occur in the tapping process, the causes, and solutions, and I hope to help you minimize the occurrence of the above issues during the tapping process.

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