Thread cutting - useful information
Geometries on the tap
When tapping threads, the geometry of the tap is particularly important. Materials have different chip behavior and using the wrong tool can lead to welding, chip jamming or tool breakage. For this reason, all dimensions on the tap must be precisely designed for the intended use.
Here you can find further information on: Designations, geometries and definitions on taps
Cutting speeds and lubrication/cooling
In order to increase the service life of the tools and produce threads of maximum quality, the cutting speed and cooling lubricant must be selected correctly. This is the only way to ensure time and cost-efficient work in the long term.
Here you can find further information on: Cutting speeds and lubrication/cooling
Bleed
The lead of the tap must be selected according to the material and the type of hole. The choice of lead shape influences the service life of the tool and the success of the thread. Lead forms differ according to the number of threads and are clearly defined according to DIN 2197.
You can find more information here: Lead forms
Problems with thread cutting
Difficulties with thread cutting can often be traced back to errors in the choice of tool, machine settings or the use of cooling lubricant. We have compiled widespread problems and their most common causes in a table:
| Thread too tight | - Pitch error - Tolerance position too low - Forced guidance too strong |
|---|---|
| Thread too large | -cutting speed too high - Concentricity error - Chip jam in grooves - Offset tap to hole - Incorrect feed - Tolerance position too high |
| Poor thread surface | -cutting speed not optimal - Lubrication not suitable or available - Cutting geometries unsuitable for material - Core hole too small |
| Thread breakage of the thread to be cut | -cutting geometries unsuitable for material - Core hole too small - Core hole not deep enough - Chip jam in grooves - Concentricity error - Offset tap to hole - Incorrect feed rate |
| Low tool life | -cutting speed not optimal - Lubrication not suitable or available - Cutting geometries unsuitable for material - Surface treatment/coating required for tap - Core hole too small |
| Tool break-outs | -cutting geometries unsuitable for material - Core hole too small - Core hole not deep enough - Chip jam in grooves - Concentricity error - Offset tap to hole - Incorrect feed - Worn tap |
| Welding on the tap | -cutting speed not optimal - Increase coolant supply |
Formulas
It happens from time to time that calculations have to be carried out during thread cutting. Even if the required values are already known, it is an advantage to know the formulas behind them. We have compiled a clear overview of all the formulas required for thread machining:
