Tolerances for cutting dies
Tolerances specify the extent to which the actual dimension may deviate from the perfect target dimension during thread cutting. In this way, a correct fit of components is guaranteed even with small fluctuations. Tolerance classes can be divided into fine, medium and coarse. Different abbreviations apply depending on the type of thread.
ISO metric thread to DIN 13 - standard thread and fine pitch thread
4h = tolerance class "fine"
6h = tolerance class "medium", for small dimensions (up to M 1.4)
6g = tolerance class "medium" - standard
6e = undersize tolerance; for studs that receive a surface treatment or galvanic protective coating (with coating thickness up to approx. 8 µm). Dies with 6e tolerance cut approx. 0.03 mm smaller than dies with standard tolerance 6g.
8e = undersize tolerance; for studs that receive a thick coating (layer thickness approx. 16 - 18 µm)
Unified thread UNC, UNF, UNEF, UNS, UN, UNJC, UNJF, etc.
3A = Tolerance "fine"
2A = Standard tolerance "medium"
1A = Tolerance "coarse"
Whitworth pipe thread G according to DIN-ISO 228
A = Standard tolerance "medium"
B = Tolerance "coarse"
Terms and explanation of dimensions
Explanation of symbols
D = Outer diameter
E = Width
a = Tooth width
c = Groove width
b = Diameter of the holes for the retaining screw
α = Rake angle
β = Chamfer angle, half countersink angle
γ = Peeling chamfer angle
Workpiece preparation
For optimum results when using dies, it is particularly important to prepare the stud correctly:
- Select a suitable stud: The stud preparation diameter must be less than the nominal diameter
- Chamfer the stud centrically: this makes cutting easier
Bleed
Similar to taps, there are also different chamfer shapes for dies:
- Standard chamfer: exact length varies depending on the die
- Short chamfer: 1.25xP with 70° chamfer angle
- Peel cut: Improved chip flow and reduction of the cutting torque for a higher surface quality of the thread and a longer die life