37 Rock Drilling T ools 800 8726899 Brunner Lay R oc k Bit Car e The total life or distance that a rock bit will drill depends on many factors Of these rock bit reconditioning can be the major factor both in the cost and performance of any rock bit button or rooftop insert BODY WEAR EXCESSIVE PROTRUSION WORN FLUSH WITH BODY SURF ACE FRACTURING DULLNESS OF CUTTING EDGE WORN OUTSIDE CORNER REVERSE GAUGE SURF ACE FRACTURING Button Illustration 1 Button bits should be reconditioned when the body wears away faster than the button wears causing it to protrude excessively This will prevent the button from pinching or shearing of f This frequently happens in softer abrasive ground 2 When the button wears at a more rapid rate than the body especially in harder more abrasive rock the buttons should be reconditioned frequently 3 Button bits should be reconditioned if the buttons polish or show signs of surface fracturing in nonabrasive rock This will prevent the surface fractures from propagating which could result in fracturing the buttons R ooftop Illustration 1 Rooftop bits should be reconditioned when the dullness of the cutting edge is 332 25mm fat measured on the gable halfway between the centerhole and the outside diameter of the bit 2 A bit should be sharpened when the outside corner of the insert has worn in excess of 316 50mm radius 3 Rock bits should be gauge ground when the bit begins to reverse gauge 4 In nonabrasive ground a bit should be sharpened periodically to remove any high polished area of the insert or surface fracturing to prevent the surface fractures from propagating which could result in a fractured insert