General Information on Sharpening
Drill Bits

Typical Grinding Media Used
  • SB-250 Black Grindstone, graded course
  • DC-250 Diamond Wheel Course
  • CBN wheel : 150-180 grit
  • Very friable grindstone : 80 - 100 grit

Shaping the Tool - Drill bits are typically not reshaped. The general guidelines for a shape work well in many situations, and are probably fit for the average user.

However, there are plenty of studies (e.g., Drill Bit Geometry, by Joseph Mazoff) linking the geometry of the drill bit's cutting edge to the power needed to perform the drilling operation. When more power is needed, two things happen :

  1. A lot of heat is generated in the drilling operation -- this can damage the piece being drilled, especially if it is a very hard wood like ebony which cracks with high heat build-up. Additionally, the drilling operation may affect the mechanical properties of the workpiece by creating low residual stresses around the hole opening and a very thin layer of highly stressed and disturbed material on the newly formed surface.

  2. The drill bit gets dulled quickly -- and, depending on the quality of the bit used, it may not be able to take that much heat.

It may make sense for the user get a separate set of drill bits for commonly used processes (e.g., a set for steel, one for aluminium, one for wood, etc.).

Typical Grinding Media Used
  • SB-250 Black Grindstone, graded fine
  • DF-250 Diamond Wheel Fine
  • CBN wheel : 250+ grit
  • Very friable grindstone : 150 - 180 grit

Sharpening the Tool - All the drill bits to be used for a job should be sharpened at the start of the job for which they will be used, and as often as necessary (which is more often than most people resharpen them). This includes not only the one used for the final hole size, but all the ones leading up to that.

Resharpening during the middle of a job may make sense as it will make the job go better, and potentially yield a better result. This is particularly true if the piece is to be reamed as a nicely drilled hole will be easier to ream.

The benefits of a 4-facet grind over a 2-facet grind are well outlined in Drill Bit Geometry, by Joseph Mazoff. This is highly recommended if your sharpener can accommodate it.

Honing and Stropping
to remove the burr
Typical Grinding Media Used
  • SJ-250 Japanese Waterstone
  • DE-250 Diamond Wheel Extra Fine
  • CBN wheel : 250+ grit

Honing the Tool - Many users of drills do not hone their drill bits.

My experience has been that using an un-honed drill bit which will work adequately when performing rough work; however honing is recommended when drilling softer metals, hard woods (e.g., ebony), and especially burls in hard woods.

Note: When honing or stropping, the side to start on is the one where the grinding was last done. If you start on the other side, the burr will get ripped off and you can end up with an edge like above.