Drilling wears down the cemented carbide in inserts and buttons. Most of this wear is caused by abrasive action at the sides and bottom of the hole as the drill bit rotates. If nothing is done about this wear, the rate of penetration will drop and the inserts, along with the rest of the drill swing will be subjected to abnormally heavy stresses. For this reason, cemented carbide must be reground at regular intervals to restore its original shape. Different kinds of rock cause different degrees and patterns of wear.
Face wear occurs when drilling granite, gneiss and other hand rocks. The cemented carbide tip wears down and develops a wear fiat which, on brazed inserts, grows wider towards the outside because of the greater distance travelled by the outer section of the bit. The gauge buttons on a button bit also wear faster than the face buttons.
Gauge wear occurs in abrasive types of rock with a high quartz content. The cemented carbide on Te outside of the bit suffers abnormal wear, resulting in what is referred to as "anti taper" and the bit loses its clearance angle.
Snakeskin is the condition that develops when drilling in rocks that have very little abrasive effect on cemented carbide. The surface of the carbide suffers from fatigue and a pattern of hairline cracks, very similar to snake skin, develops, particularly on the corners of the insert. These shallow, hairline cracks must be removed as soon as they appear. Otherwise they will spread deeper into the tungsten carbide and cause chunks of the material to break off. When drilling in some types of rock, there are no visible signs of wear at all. The cemented carbide should still he reground to prevent the formation of fatigue damage. In such cases, the recommended grinding intervals for buttons are 300 metres and for brazed inserts 150 metres(500 ft).