Cutting dies tolerance classes

If no tolerances are specified in the order, then we supply dies for ISO metric threads to satisfy class 6g tolerances (P=0,25 tol. 6h), dies for Whitworth pipe thread to satisfy class A tolerances and for dies for Unified National thread to satisfy class 2A tolerances. We also manufacture dies for ISO metric
thread to satisfy 4h, 6h and 6e tolerances, dies for various undersize Whitworth pipe thread and dies for unified national thread to satisfy
class 3A tolerances. These tolerances zones, however, must be specified in the purchase order.

The following applies:
4h for ”fine” class tolerances (bolt remains uncoated or is thinly phosphated);

6g for threads over 1.4 mm dia.
6h for threads up to 1.4 mm dia.
for ”medium” class tolerances (thread stays uncoated, is phosphated or is only thinly electro-plated);

6e for ”medium” class tolerances (thread is heavily electro-plated).
6e dies cut threads approx.
0.03 mm smaller than 6g dies.

Dies to suit threads with other tolerances are available on request.

Preparation of workpiece

A chamfer has to be machined concentrically on the workpiece on which
the thread is to be cut. Easy starting of the thread and a concentric thread are thereby achieved. The workpiece diameter must be less than the nominal diameter (see guide lines in tables on pages 88 to 91), so as to avoid cold welding in the die at the thread major diameter and tearing of the threads. Chipping of the die on reversal is avoided, if there is an undercut at the runout of the thread.

Chamfer

Standard chamfer:
The length of chamfer is given in the price tables.

70° (short chamfer):
Where threads have to be cut close to a shoulder, we supply dies with a chamfer length of approx. 1.25 pitch =ˆ70° chamfer angle. Customers cannot shorten the chamfer by surface grinding, as this results in a chamfer diameter that is too small, so that the die then no longer cuts properly.