Single Crystal Diamond (SCD) Toolmaking
Introduction to SCD tool making
To turn or mill the very best surface finishes on plastics, aluminium and copper for example, single crystal diamond tools are needed. SCD tools can produce much better surface finishes than even the finest grain PCD tools.
However, single crystal diamond tools are more difficult to make than PCD tools because diamond crystals have both "hard" and "soft" directions. This is true for both natural diamonds and synthetic diamonds. The "soft" or easy grinding direction of diamond are shown below.
If you try to grind even a few degrees away from these directions then very little progress will be made.
How to grind any diamond in its soft direction
On a scaife bench the position of the diamond can be changed on the plate or the dimaond can be rotated. The soft direction can be found. For a radiused cutting tool a grinding machine with a pivot is used. The tool is in a fixed position. The soft direction can be found by moving the wheel relative to the diamond.
These machines are therefore called "planetary" grinding machines as the grinding wheel spins but also moves like a planet around the sun (the diamond).
Wheel position - Hard Direction
Normally the wheel (grey) rotates anti-clockwise.
With the wheel positioned at the 3 o'clock position, the griding direction is vertically downwards as shown. The diamond (yellow) has soft directions shown in red.
In this position the wheel is trying to grind the diamond in the 'hard' direction and little if any progress will be made.
Wheel position - Soft Direction
By moving the wheel (grey) to the 4:30 o'clock position, the direction of grinding is now parallel to one of the soft directions of the crystal and the diamond can be ground easily.
Click this link for more information on planetary grinders.