As my reamers are very close to size at the tapered end, I need to get within .005" of the finished hole size before the reamer will enter the hole without a great deal of force so often I need to drill close to the final size then bore until within .005" of final size and then ream, my main reason for doing this and not boring to final size is that I don't have a huge amount of success getting repeatable results from my expanding bore gauges - there seems to be a bit of skill needed in using them. In the lathe it is not so bad as you can move the saddle back to give your self room but in the mill the expanding gauge is often at an odd angle, I can measure the hole with the expanding gauge 4 or 5 times and sometimes there might be 1 or 2 thou variation over the measurements which for close fit sliding parts can be too much, so if I use a reamer for the final sizing of the hole I'll know it is right on.
