Thread Rolling Dies: What They Are and How to Handle Them

What a rolling die is

A rolling die is the tool that forms a thread on a thread rolling machine by plastically deforming the metal.

Precautions when using rolling dies

1. Do not run dies on a machine with poor accuracy, heavy vibration or abnormal operation.
2. Misaligned dies let the workpiece move axially, so the thread profile is loaded in both shear and compression.
3. Blanks of uneven size, or with grinding dust, scale or dirt left on the surface, damage the profile.
4. Blank hardness must be uniform — grade 8.8 bolts should be 27–30 HRC and grade 10.9 about 35–37 HRC. Untempered hardened parts at 50–55 HRC mixed into a batch will chip the die, because their hardness approaches that of the die edge.
5. Roll without lubricant and the dry friction raises the tooth-tip temperature above the die tempering temperature, softening the profile and causing collapsed or flattened threads.
6. Dies must be fully demagnetised before shipment; residual magnetism attracts fine iron dust and accelerates wear.

Die pitch is not matched to diameter — the pitch is fixed while the diameter varies. Several diameters exist for a given pitch, so choose the pitch first, then the die diameter that suits the workpiece being rolled.