David,
This is the set of files that I have modified to be used in reverse in my variable speed drills to ream cork rings, as well as grips.
The place where I took rod building lessons used similar files to ream all of their cork and it worked well. So, over time I assembled a set as well.
I first used a cut off wheel to remove the triangle handle that is normal on these files. Then, I chucked the small end of the file in my lathe and used a grinder to grind a uniform circular area on the opposite end so that I can chuck that end into a drill and have the file run true.
Then, I put the cleaned up end in the lathe and used a grinder to put a sharp point on the small end. This allows me to use a larger file to start with a small hole in the cork and quickly ream it out to the necessary size.
If the file gets filled with cork or other dust, I just hold the spinning file against a spinning bench mounted wire wheel to extract everything from the file and keep it cutting well. These are the same files that I started with many years ago and hundreds of rods later they still work as well as they did when I used each of them on the first cork ring or the first grip.
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www.rodbuilding.org]
Depending on the size of the file, I use either a high speed variable speed 3/8th drill or a high speed variable speed 1/2 inch drill to spin the file.
As others have said, I always use the file in reverse so that it does not screw itself into a ring or grip and split it wide open because the file would just screw into the ring or grip without actually cutting out any cork. But, in reverse, the file is just forced into the ring or grip to remove extra material.
Take care
