JBTSAX;
Re: your post of 2-18-2012.
Did you ever use the tapered mandrels on your instrument? Did you remove any significant wood to make it conical or did it just need polishing? Does it play with essentially correct octaves? The reason I am interested is that George changed the bore on his instrument to be really conical and had success with sharping the upper octave. I am tempted to do this to my TSO, but incrementally, with frequent reassembly/playing tests. Actually, I could not resist and did apply my homemade single flute reamer (1:18.5) to the TSO. After removing only a tiny amount of wood (and a lot of sandpaper-clogging crud), the lowest notes became much easier to play, and D at the bottom of the second octave is much sharper. It seems like progress.
. . . C.S.
You are entering a world that one great acoustician (Art Benade) described as "three dimensional chess". If you study Rayleigh perturbation theory, you can actually predict what effect removing or adding material at any point will have on intonation of all notes on a horn. In a nutshell, constricting a bore will raise pitch if the point of constriction falls at a pressure antinode of the wave of the note in question, and will lower the pitch if it falls at a pressure node. Increasing the bore has the opposite effect. The amount of the effect will depend on how close the perturbation is to the node or antinode. Each note has nodes and antinodes at different places in the bore, so any perturbation will affect all notes, some in one way, some in the opposite way, and all to different degrees. So the risk is that if you don't know what you are doing, you can easily fix one note or several and make a number of others much worse. With conical instruments, you can easily ruin the whole instrument.
In making shakuhachi flutes, even experienced makers often remake the bore (it is built up in hollow bamboo with a kind of putty, so it can be redone) thirty to fifty times until they are satisfied with it. I just want to warn you that you might be opening a huge can of worms, even more so since the intonation of an instrument is also heavily dependent on the design of the mouthpiece. It is, of course, much better to adjust a mpc to the horn than trying to adjust the horn to the mpc. Only after the mpc is optimized is it advisable to even think about changing the bore, with the knowledge that one can ruin an instrument with ease.
When I first got my alto sax, I found it completely out of tune. I spent a lot of time putting different sized crescents in the tone holes. As I played, I kept adjusting, until to my surprise I had removed all the crescents except one. The moral here is that it was not the horn that was at fault, it was my playing. But my crescent involved only gluing rubber strips inside the tone holes, a completely reversible procedure. What you are talking about is not reversible.
With that being said, it is absolutely advisable to smooth the interior of the bore--that will certainly make playing easier and response better. Generally speaking, doing this with sandpaper will slightly increase the bore diameter, but it will do so in equal proportion along the bore. Changing the cone angle locally can have very undesirable effects, and a straight cone is not always desirable: while theoretically only a cone gives perfect harmonic intervals, unavoidable real world compromises such as the space under tone holes, and the fact that the top of the cone is chopped off to provide a place for a mouthpiece, destroys this theoretical nicety. Makers almost always make local adjustments to the bore geometry to compensate for these realities--such as the cylindrical "necking in" at the top of the bore, and others as well.
Just be aware of these things as you make your way.