Why would you say the TiN coating is defeated when sharpening a twist drill bit? These bits are sharpened by removing material from the relief, which does not require the coating to aide the cut only the lifting face.

Answer

The TiN coating surface hardens the drill bit and helps to prevent friction from wearing the core and flutes. However, if the cutting edge is sharpened, the coating is removed in that region. So, that's likely to degrade performance at the tip and cause more rapid wear.

Updated on March 8, 2018

Original Article:

Choosing the Right Drill Bit for Metal, Wood, Tiles, Glass, or Masonry
By Eugene Brennan
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