repair cost
4.The low fragmentation efficiency and the inferior geometry stability in fragmenting hard rock with strong abrasiveness can lead to uncircular hole,low drilling rate,short life,frequent repair grinding,high regrinding cost,low alloy utilization rate,increased mechanical troubles and auxiliary working hours and deteriod labouring conditions. Therefore,cone connecting cross bits and button bits have been used in replace of chisel bits since the middle of Seventies.

