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.

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.

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.

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.

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.

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.

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.

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.