Boride's Stoning Basics

When choosing a stone to begin polishing a mold or die there are many factors that must be considered. A few of the most common are listed below:

A. Mold Material

Steel (P20, Stainless Steel, H13, D2)
Non Ferrous (Aluminum, Bronze)

B. Material Hardness

• Soft
• Hard
• Heat Treated

C. Finish quality left by the machining process

• EDM
• Milling
• Grinding

D. Shape of mold surface

• Flat
• Radius
• Rib or Slot
• Detail area

E. Desired final finish

In general, it is always better to start with a finer stone. If a coarser stone is needed, you can always go coarser to achieve the best result.

In most cases, you can start with a 220 grit stone for conventional machined surfaces. EDM surfaces may require a coarser grit stone to remove the hard re-cast layer.

For ground surfaces, a finer stone can be used to start the polishing process.

For radius surfaces, it is good to use a softer stone that will take the shape of the mold.

For detail areas that require a mold feature to be maintained, it is better to use a harder stone that will keep its shape.

Always use a lubricant with harder stones to prevent stone loading.