This troubleshooting guide identifies the causes and solutions for common tapping problems: threads produced too large or too small, axially miscut threads, poor thread surface finish, insufficient tool life, and tap breakage during advance or return. The guide covers tap selection, tapping size hole specifications, machine setup, cutting parameters, and toolholding for both spiral fluted and spiral point taps.
Why is the thread produced too large?
Threads produced too large result from incorrect tap selection, undersized tapping holes, alignment errors, spindle restrictions, cold welding, insufficient thread depth, excessive cutting speed, or inadequate lubrication.
| Possible Causes | Solution |
|---|---|
| Incorrect tap, tap geometry not suitable for the application | Apply correct tap material to be machined |
| Tapping size hole is too small | Observe tapping size hole table in the technical solutions. Note different tapping size whole diameters for fluteless taps. |
| Alignment error of tapping size hole or position | – Check for correct tool clamping<br>- Apply floating tap holder<br>- Check core drill |
| Machine spindle axially restricted | – Use mechanical feed<br>- Apply tension/compression tap chuck |
| Cold welding at the flank of the tap | – Apply new tap<br>- Apply coated tap<br>- Optimize lubrication |
| Lead of tap unsatisfactory due to insufficient thread depth | – Tap with forced feed<br>- Apply tap with modified lead |
| Cutting speed too high | – Reduce cutting speed<br>- Improve lubrication |
| Lubrication or coolant supply insufficient | Ensure sufficient and suitable coolant supply and check concentration |
What causes thread axial miscut?
Thread axial miscut occurs when tap tolerance specifications do not match drawing or gauge requirements, or when initial tapping pressure is incorrect for the tap design.
| Possible Causes | Solution |
|---|---|
| Tolerance specification on tap does not correspond to specifications on drawing and/or thread gauge | Apply correct tap for required tolerances |
| Spiral fluted taps, corresponding to our design are applied with too much pressure for initial tapping | With spiral fluted taps only light pressure required for initial tapping. The tap should immediately be applied within the tension/compression range. |
| Initial tapping pressure too low for taps with spiral point corresponding to our form “B” | Taps with spiral point or left hand spiral require higher axial pressure. Ensure tap operates with the tension/compression range |
Why is the thread produced too small?
Threads produced too small result from incorrect tap tolerance specifications, wrong tap selection, inaccurate cutting verified by thread plug gauge, or excessive axial rigidity in the machine spindle.
| Possible Causes | Solution |
|---|---|
| Tolerance specifications on tap do not correspond to specifications on drawing and/or thread gauge | Apply correct tap for required tolerance |
| Incorrect tap | Apply correct tap for the material to be machined |
| Tap does not cut accurately (thread plug gauge) | Avoid strong axial forces during the cutting process |
| Machine spindle is axially too rigid | Apply tension/compression chuck |
What causes poor thread surface finish?
Thread surface not according to requirements is caused by unsuitable cutting edge geometry, excessive cutting speed, insufficient coolant, chip congestion, undersized tapping holes, or excessive loading on tough or hard materials.
| Possible Causes | Solution |
|---|---|
| Cutting edge geometry not suitable for the application | Apply “correct” tap for the material to be machined |
| Cutting speed too high | – reduce cutting speed<br>- optimize lubrication |
| Insufficient coolant (concentration and supply) | Ensure suitable coolant and sufficient volume |
| Chip congestion | Apply suitable tap type |
| Tapping size hole too small | Observe tapping size hole diameter specifications to DIN 336 or respective standards. Observe table for fluteless taps |
| With tough, hard materials loading on tool too much or pitch too steep | Apply hand taps sets |
Why is tap tool life insufficient?
Insufficient tool life results from built-up edge, cold welding, surface hardening of the tapping size hole, chip congestion, or any of the causes listed under thread surface problems.
| Possible Causes | Solution |
|---|---|
| Built up edge | Apply coated taps |
| Cold welding | Improve coolant supply |
| Surface hardening of tapping size hole | – check drill (cutting edge) for wear<br>- Heat or surface treatment following thread production |
| Reasons listed under “thread surface not according to requirements” | Reasons listed under thread surface “not according to requirements” |
| Chip congestion | Apply correct tap |
What causes tap breakage during advance or return?
Tap breakage during advance or return occurs when the tapping size hole is too small, chamfer lead teeth are overloaded, the tap hits the bottom of the hole, the tapping size hole has incorrect chamfer or positional errors, or tool hardness and cutting edge geometry are unsuitable.
| Possible Causes | Solution |
|---|---|
| Tapping size hole too small | Observe tapping size hole dia. Acc. To DIN 336 or respective standards |
| Teeth of chamfer lead overload | -longer chamfer lead (blind or through hole)<br>- increase no. of teeth of chamfer lead by increasing no. of flutes<br>-apply tap sets |
| Tap hits bottom of tapping size hole | -check hole depth<br>-apply tension/compression tap chuck |
| Lack of or incorrect chamfer of tapping size hole | – Correct chamfer angle of tapping size hole |
| Positional or angle error of tapping size hole | -ensure correct tool clamping<br>-apply floating tap holder<br>-check core drill |
| Tool hardness not suitable for the application | Apply suitable tap for individual application |
| Cutting edge geometry not suitable for the application | Apply suitable tap for individual application |
Tapping size hole specifications
Tapping size hole diameter specifications follow DIN 336 or respective standards. Different tapping size hole diameters are required for fluteless taps compared to standard cutting taps.
Source and updates
Source: taylortool.com engineering data.