How can I tell which direction the blades should rotate if I can’t see the arrow?
Look at the segment closely. The grains of the diamond will have a tail behind them, (Like a comet). Mount the blades so the tail follows the grain of diamond when rotating.
Why is it important to match the blades to the Material being cut?
Soft Material is easy to cut but very abrasive, so the diamond segment needs to be hard to slow the rate of wear. Hard Material wears the grains of diamond quickly so the segment is soft so the worn diamonds can be released sooner and the fresh diamond within the segment is exposed. Summary –Hard material/ soft segments, Soft Material / Hard segments.
What will happen if I use the wrong blades?
If a soft segment is used on a soft material, the segment will wear very quickly. If a hard segment is used on a hard material the segment will go smooth and not cut. Then the blade will be rubbing when cutting and get hot. When hot the blade may become damaged.