Solid horn - work in progress

Hi all!
I'm building the second horn for my RCF Nd1710 mt3 audio driver, 1" exit , 108db/w/m, 1-20khz range, titanium diaphragm and strong magnet.

The big boy is a 130mm round bar, normal aluminum that melt on tools :rolleyes:

I chose tractrix contour, I tried it many times in the past, it works perfectly for home use for middle and high frequency.


Probably I will buy a good finishing tool


Some pictures of the horn , still work in progress

Saluti
Stefano

Attachment 25906 Attachment 25907 Attachment 25908

Attachment 25909 Attachment 25910 Attachment 25911

Attachment 25912 Attachment 25913 Attachment 25914

Attachment 25915

Aluminum streamers today! :D

The raw profile of the horn is done, with the lathe at limit. My endowment of boring bar is limited, for this tool I have no new carbide tips. Unluckily the only right tool I have, it's short and tiny, not enough for this job but I do what I can.
Now it's time to use the files, lot of sand paper and finally wool and polish!

I'm having some trouble about vibration using boring tool and up to 20° angle, have some good advice in order to have a good smooth surface?
thanks
Stefano

Attachment 25942 Attachment 25942 Attachment 25943

Attachment 25944 Attachment 25945 Attachment 25946

Attachment 25947

Wow. Nice. :)

Thank you Tuomas!

It is a crying shame that the true acoustics of your builds can never be experienced coming from the speakers or headphones of our computers.
I liken these to that of trying to experience the effects of a performance in a symphony hall from an ear bud on a 2 transistor am radio.

You're right Frank! I hope I will be able to describe the sensations!
The good thing is that with only one watt you can have 108db at 1 meter, so even a tiny amplifier with no caps and few components can make the difference

Ps: I'm close to sand paper work!

Attachment 25983 Attachment 25984

Ready to polish the inside of horn… unluckily I can't use cotton wheels and normal paste.
I'm trying to make a "grease" paste with powder, I hope it will be good!

Attachment 25986 Attachment 25987 Attachment 25988

If you can't find any jewelers rouge then a wad of lambs wool on a stick and tooth paste usually works for me.

Some work of adjustment, lot of sand paper needed, lot of passion.
I prepare a second special recipe for the polishing paste with lithium grease and oil, it should work fine, at least it can stick better to surface. The trouble is that I can't push so much to increase heat, like with cotton wheels. Another trouble this soft aluminum is a crap to polish compared to ergal, scratch are behind every corner.
I'm thinking about the next step, Last time I build brass long feet from solid bar (H frame), maybe I will machine a couple of rods fixed directly to the horn.

Attachment 26002 Attachment 26003 Attachment 26004

Attachment 26005 Attachment 26006

Hi all!
Lot of time with sandpaper, from 60 to 1500 grit, about 5 hours to polish both, I still need half an hour, the abrasive mix with grease and oil is hard to clean inside the horn, in first picture there is the veil on the surface.
I have to finish the adaptor, and thinking about the pedestal, I found 25mm solid brass round bar that seems perfect for the purpose, I'm still undecided if make a stand alone unit or fix to the horn through screws.

Attachment 26027 Attachment 26028 Attachment 26029

Attachment 26030 Attachment 26031 Attachment 26032

Attachment 26033 Attachment 26034

Looks great!

Thank you Tuomas!
I have to clean with patience, the grease veil is hard to dissolve even with brake cleaner!

Next thing I have to built a no compromise rest. I'm thinking about an adjustable unit with different axis involved, since the horns are something important, i would like to finish the project at maximum of my skills