Diamond core bits must maintain good diamond exposure in order to work efficiently. Many factors work in unison to provide the controlled erosion cycle of the bit's segments. When this controlled erosion cycle is altered, the bit can become dull or glazed. Glazing becomes noticeable when the coring feed rate slows dramatically or the bit does not cut. Examine the bit immediately. If the diamonds are flush with the metal, they are underexposed or glazed. The following steps will often correct this problem:
- Reduce water flow until it becomes very muddy. Continue using as little water as possible until penetration increases.
- If bit does not open up, remove from hole. Pour into kerf a thick (1/4") layer of silica sand, the coarser the better.
- Resume coring for approximately 3 to 5 minutes with very little water and at a lower RPM if possible.
- Gradually increase water flow to flush sand from kerf.
- Repeat as needed.