fwiw I sand down each flat to 400 grit (100, 150, 220, 320, 400) using a small glass sanding block and use 0000 steel wool for final smoothing. that said I've never worked on or built an impregnated rod. it's not that tough and I wouldn't worry about it. it gets toughest to maintain the hex profile while varnishing, especially over the wraps near the tip. be advised you can sand these as well (I use 1000 grit or even finer). the wraps will look like hell but the next coat of varnish cleans them up.