When I got into rod building the first thing I discovered in the archives was that I needed a tapered reamer to fit the cork grip to the butt section. As instructed I found an old rod removed the guides and cut it into 15 - 18 inch sections. There were several ideas presented here and from friends on abrasives and how to apply them to the rod sections. The best I have found is a 1/4" strip of self adhesive 3M stair tread spiraled down the peice of rod leaving a 1/8" gap to catch the dust. This reamer will last forever and cut quick so check the fit often. If you turn your reamer clockwise wind the strip of non-skid clockwise also to keep it from unpeeling.
I found the 3M non-skid at the local lumber yard for about $1.70 a foot. It's a couple of inchs wide so you can make several different size reamers.