I have found that the holes produced by drills can be highly inaccurate, caused by a multitude of cutting conditions like lubrication, materials, cutting speeds, feeds, and of course the big one - sharpening, how many people can sharpen a drill accurately? - not many! Always drill undersize and use a reamer (if possible) when accuracy is required. Yes, the adjustable reamer is very good at taking out a whisker at a time only, but it needs to be set squarely to the hole to be reamed and the best way to do this I found to do this was, when possible (not always possible of course) put the work in the chuck and line up the reamer with the tailstock centre and turn the reamer by a spanner or tap handle, following up with the tailstock all the time. Once I became more bold, I actually did it successfully many times with the chuck turning and holding the reamer in a drill chuck! - however, one day I got ahead of my capabilities and wound the reamer up till it broke! This is definitely not the way to do it!