A little update:
I have been using Cube Audio 600Hz tractrix horns on the upper mid channel with the Vitavox S2 drivers.
Freq range ~1200Hz - 12000Hz.
The are made of Glass Fibre / a composite material.
I thought I'd try wood instead and go for a slightly bigger tractrix.
Having glued some rings of birch ply together I turned the first section
Quite hard to see inside so a little push bike light illuminates
Then into the larger section
I made a profile gig to check I was getting the right tractrix flare.
Then glued them together and turned as one
Next was to make the screw on adapter rings for the S2's
a 16TPI Whitworth thread.
I decided to use something easy to machine yet strong enough for the fairly light horn
Plastic
Mounted up on a drive plate
Inside threading bar to make the thread cut
Lathe leadscrew gearing set to 16TPI. It needed several cuts.
Moment of truth - does the driver screw on?
Yay
Nice fit too.
spray filler and spray painted to match the system
Adapter centred and mounted
All set
Now do it all again for the other one
Listening impressions are good. Very fluid and integrates really well.