Whereas a chisel can be sharpened for years without noticeably shortening its life, the cutting head of an auger bit has not metal to spare. Bits should therefore be treated with fanatical restraint. Remove the least amount of material to restore the cutting edges.
A tapered auger bit file and a slip stone are the tools you need.
Aldren A. Watson, Hand Tools: Their Ways and Workings, 1982
The true use of an auger bit file is to clean up binding rabbets on a guitar.
It does a crackerjack job, it doesn't remove too much material at a time, it's thin enough to work in the binding pocket where the neck meets the top and I can use it to sharpen my auger bits (I have a separate file just for that task).
A very handy little file.
Finished bindings on a Western red cedar/Indian rosewood concert guitar.
Along with the auger bit file, I also use emery boards to clean rabbets, they are especially useful at the guitar's waist, always a tricky spot to get right.
Work continues in my shop, three guitars are keeping me busy at the moment. When all of those are completed I will have four guitars that need to be French polished.
Did I mention I need to build a new workbench? My the joints on my old "Roy Underhill-esque" are getting loose, she rocks too much anymore and it always was too light in weight. I have plans for a new one made out of alder and Douglas fir.
Did I mention I need renovate my workshop?
Too much work and not enough time.
Here's a video of my former classical guitar teacher, Warren Haskell.
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