Full Chisel Blog

July 11, 2013

Sharpening a Gedge or Cooks Pattern Auger Bit

Filed under: Drilling,Historical Material,Of Interest,Proper Tools,Sharpening,Techniques — Stephen Shepherd @ 9:35 am

I received a request about how to sharpen a Gedge or Cook pattern auger bit from someone who follows my blog, and I realized I had never posted about how to sharpen this type of auger before.  This is a great bit because after the led screw engages the auger bit can be tilted to almost any angle and the unique nature of its engineering allows it to cut a perfectly clean entry hole with no tear out or chipping.  And the spelch looks unusual.



It is absolutely crucial that the top flat remains flat, no micro bevel devil or stupid tricks for getting this type of bit to cut properly.  Try any of those hair brained ideas on this bit and it will get stuck in the hole, if it can make a hole.



With a fine flat file gently get the top to a shiny edge keeping the file flat on the back.  It is just like a chisel or plane blade in that you want it flat.  You can also use a small whetstone to accomplish the same purpose but keep it flat.



Any chips or irregularities on the cutting edge is dealt with from the inside flat bevel.  The inside on my two bits are very flat as well with no improper filing of an additional small bevel, so keep it as flat as possible even on the inside.  The smaller bit [7/8″] made by Marples had what looked like a small chip perhaps made while hitting a nail?



I corrected the problem by filing it from the inside.  I used two sizes or round chain saw files to work the inside, however a round slip whetstone would have worked.  I filed the inside curve from both the top and bottom, the sweep takes a little practice to follow.



Once I felt a slight burr on the top, I was finished sharpening.  I don’t bother removing the small burr as it will go away after the first few times I use the bit.  The larger bit [1 15/16″] is a Cooks Pattern Patent dated 1851.  Never improperly filed it sharpened up quickly.

Here is a link to a video of this bit in use.


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