A couple questions about horn shaping
1. Should the butt of the horn be shaped to be uniformly round, more specifically, a period correct method? I don't have a lathe to turn a shaping cone. I do feel confident I can get a nice finish by working the wood with files and rasps for a good fit and finish without using a shaping cone. Any advantages or disadvantages to not using a shaping cone?
2. The spout of the horn is not perfectly round which is probably a common fact. I used a compass in the centering hole for the drill bit to see how out of round it was. Should I scrape the excess before starting to layout the panels or just work everything down and hope I can even out the panels as I go?
# 1. Is not an easy question to answer, some what depends on the style of horn you are making. If you don't have a lathe to turn a shaping cone then you wouldn't be able to turn the base round to fit. Yes, it can be done but is time consuming. Most original horns I have seen with a natural base are what I call a homemade horn, very simple architecture.
To use the natural opening first work you horn down to shape, try and taper the horn uniformly along its entire length. You mentioned Panels, here is a Tutorial that may help you with that. You can shape the spout area before doing this or after. Try to get the base of the horn to as uniform thickness as possible. Once you have what you want make sure the base is square, a board with 80 grit sandpaper wrapped around it works well, set it on window to make sure. Then set it on a board, 3/4" will work but is a little thick. Trace around the horn, put witness marks on the horn and the base so you know where to put it together every time. You may want to orient the wood grain N-S or E-W, no tech reason it just looks better. Now using a Coping saw, if you have one, cut it out, on the line as close as possible. If you don't have a coping saw you can cut it square and rasp it out to the line. Still won't fit so take a pencil, and using your figure as a guide draw a line about 3/16" around the inside of the base. Now rasp front to back to that line, should be about a 10 deg taper all around. When your close take a soft pencil and darken the inside of the horn for about 1/2". Line up your witness marks and see if the base goes in the horn at all. If it does you will see graphite on it. File that off and reinsert, repeat, rubbing with pencil as needed, until the base fits to your liking, for a Domed top leave 1/4" or so standing proud. Put the base in, this is before attaching and blow in the tip, it should be air tight. If there is just a little leakage you can use glue, should seal things up and pins to hold the base in.
#2. The spout should be round or close to it, try for an even thickness around the hole.
Kind of long but I hope it helps.
Tim C.
http://americanlongrifles.org/forum/index.php?topic=34423.0