The ratio was derived from the actual Rudall & Rose measurements I mentioned earlier and actually matches them quite nicely: overall the measured bore is quite straight in its slope, and especially so in the mid-section, for which this reamer is intended.
The wood is maple; if I have to guess it's because it is smooth and malleable but at the same time strong enough and not particularly sensitive to friction. (That is, with pearwood at least you often smell smoke when drilling it...)
I started out trying to make the reamer in steps of 1 mm, until I was instructed to do it smoothly from the hand. Whew!
But I succeeded, as you can see below. Here, the next step is also done -- the cone is cut in half, using the blocks at the end as a guide for finding the middle. The part with just one block intact will become the reamer; a metal strip will be added, which does the actual scraping.
What I haven't quite figured out yet, is how I'm supposed to find the center of the reamer again to create a mount point, now that I've already cut the blocks in half.
