David Lim wrote:
......the bottom on the knee, the holes _below_ the open tonehole can also have an effect.....
....But in reality neither method really works....
Having no practical experience leave me at a disadvantage but are you saying that in the real world the effect of closed tonehole chimneys on a note would be equal from above and below? Can this vary from note to note?
I wouldn't say _equal_, but it does vary from note to note. I think that rather than adopting a top-to-bottom or bottom-to-top approach, you would find it better to adjust the "most critical" toneholes first and proceed to the others, in each iteration. Unfortunately I don't feel that I can say with confidence which toneholes are "most critical", my experience suggests that this can vary for each chanter/bore design. I would not finalize the back D/bottom D relationship either, before starting to work on the other toneholes, since changes in the back d can affect the A note, and presumably vice-versa.
So personally I would characterize the Ds and the As as "critical" and pay close attention to them at each iteration, before proceeding to B (which of course affects A), Fsharp, G (Fsharp affects G rather strongly), and E, in that order... at least in concert pitch. I guess that's "sort of" top-down, but I repeat several times. (I try a few different reeds as a reality check during the process, too.)
Bear in mind that the reed will have a profound impact on this tuning, so ideally you need a reed that you have the utmost confidence in before tuning a chanter, otherwise you run the risk of tuning to a less-than-ideal reed. The interplay between reed and bore is the classic chicken/egg problem for chanter design and tuning - at least, this is how it seems to me. Bear in mind that I don't have the long experience of many of the pipemakers on this forum...
Your iterative method seems excellent, especially in a system where variables are many and difficult to predict. I can also see that if you took off small amounts it would work either way. But I cannot help thinking it would be more efficient to use it from top to bottom. (I am happy to be convinced otherwise).