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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.