Help with radial horn calculations

[jmillerdoc]

Hello,
I have been eyeballing these Fostex horns for some time trying to figure out a way to make a similar design.

http://www.fostexinternational.com/d...f/woodhorn.pdf

They appear to be a little faster expansion than a tractrix but it is hard to say.

What I want to do is cut multiple radii in some 1/2" Baltic birch in the proper lengths needed to get a similar expansion. Is there anybody who can help me come up with the appropriate radii in 1/2" material to create a similar horn? All I need is the lengths, the rest is pie. I was even thinking of using some 1/4" material for the first several pieces where the expansion is more shallow if it would be necessary.

I want something about 14" deep so the first radius would be 14". Then ??? Something like 13.75, 13.25, 12.5, 11.5, etc, etc........

Jeff

[AndrewT]

Hi,
are you planning on turning them?
Do 4pieces come out of a complete 360degree turning? Or only 3 pieces?

[jmillerdoc]

I guess you could get 4 out of it. I was considering going more than 90deg but it is a good point. One could make two complete horns from one full circle cut in quarters.

I was also thinking of using two circles and staggering the radius lengths between them where I didn't use solid wedges stacked on each other but rather, about 2" wide pieces that would leave a hollow cavity underneath.

[jmillerdoc]

.

[ozziozzi]

Hi, I have experience turning tractrix horns from stacked 1" boards(cut out into rough circles first on bandsaw or with circle jig on router).
I thought of making radial horns the same way, but by basically turning a "bottom of bowl" shape or dome first and then cutting this into four 90 degree segments. Piece of cake really ;-D
Imagine cutting wedges of bowl-boiled Christmas pudding. There is no reason why "serves" should be restricted to 90 degrees--although this would mean more than one original turning to get two radial horns. Best thing about working from one turning is that horns would be identical!!!

Next step would be to fill in "sides" of horn with flat or possibly curved pieces. You can cut curves into turned piece by mounting original base onto large flat board and using a bandsaw.
This technique is commonly used in woodturning to produce those yin-yang shaped domed desk accessories eg. paper weights.
Like others here, one thing that has held me back has been the profile of radial horn. I will be watching this sthread with interest waiting for horn gurus to appear. A template would seem essential.

[ozziozzi]

On second thoughts, my lathe could not swing blanks big enough to make Fostex horns as I am restricted to 300mm (12 inch) diameter. An alternative method would be to use a turntable under the blank and a jig/profile-following technique involving a router. This technique is used to hollow chair or stool seats, but could as easily produce domes.. Again, you would need to establish a template and follow that. I have seen this in Taunton Books "Router Jigs and Techniques" or similar title. Hope this helps.