Arnaud, thanks for your continued custom, lets see if we can help...
The problems you have experienced with the diamond drill bits seem most unusual. There are clear descriptions and recommended usage on all the diamond drill bits pages. On the product page for the diamond twist drills you will notice that we instruct that the twist drills are only to be used for opening up holes, they are not for drilling holes.
The diamond drill bits however are to be used to drill holes and as we state on the product page for these they must be used with very little pressure, they must be used on the slowest drill speed setting and they must be used with water.
There are many variables which can depend on the life of your drill bit and with the diamond coating popping off like the one in your picture would usually be due to too much pressure being applied whilst drilling. Keep the pressure very light, even if the stone is very hard such as quartz. There can be a tendency to apply more pressure because the drilling takes longer through hard stones.
Another factor that will contribute to the life of your drill bits is the hardness of the stones. If you are drilling through a stone that is 8mm thick then the drill bit will not last as long as if you are drilling through a stone that is 4mm thick.
Natural stones all have different levels of hardness and if you are drilling through quartz for instance, this will wear away the diamond coating much quicker than if you are drilling through fluorite. So an inconsistency with the hardness and thickness of the stones you are drilling through may be a contributing factor.
The drill bits themselves are all quality checked and used by members of staff so we were disappointed to hear that you were unhappy. Hopefully we can resolve these issues for you.
