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Arash

Bruce Edgar Tractrix horn project

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I'm submitting this thread to post picture of project in which I try to build my first Tractrix (Bruce Edgar) horn. the fist try is a fc260 horn with ~58cm wide 25cm height and ~37cm depth. the throat is 2" and I intent to use it with BMS 4592ND as a midrange horn.

Edited by Arash Najafi

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Day 1

we have almost any tools except band saw so I used CNC router we built. very very precise machine with HDS spindle specially designed to cut BB plywood. we were not able to set the Artcam as the z axis gradually varies according to X and Y axis movement so we cut the center template of the horn in four steps in Z axis.

 

the first step was to build a fixture to keep the MDF or BB plywood in the needed incline. CNC did the job. after gluing parts we sanded it:

 

 

post-41711-0-67640000-1416328968_thumb.j

Edited by Arash Najafi

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Day 1

fixture ready to go:

post-41711-0-43520000-1416328797_thumb.j

Edited by Arash Najafi

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Day 1

first we tested on a MDF so the fixture would have the needed slot:

 

post-41711-0-61560000-1416329669_thumb.j

 

not bad. the router wanted to go to start point when it hit the MDF. except this there was no other error:

 

post-41711-0-47400000-1416329699_thumb.j

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Day 1

after cutting dado into the fixture we can simply put BB plywood there and fix it with nails and run the command so the razor will only cut the plywood itself not the fixture underneath:

 

post-41711-0-83080000-1416329866_thumb.j

 

post-41711-0-09000000-1416329978_thumb.j

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Day 1

everything as planned:

 

post-41711-0-52000000-1416330382_thumb.j

 

believe or not, no band saw could do such a perfect cut while holding the plywood on an incline. I couldn't be happier:

 

post-41711-0-88840000-1416330415_thumb.j

 

End of day 1

Edited by Arash Najafi
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Day 2

building a fixture for horn assembly rightnow. I'll have a cup of tea till the glue solidifies:

 

post-41711-0-54720000-1416383522_thumb.j

 

there are some slots in the base to avoid any movement:

 

post-41711-0-43440000-1416386030_thumb.j

 

I'll sand the fixture in a matter of minutes and then I'll go for a framework.

Edited by Arash

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Day 2

fixture is sanded:

 

post-41711-0-43560000-1416386078_thumb.j

 

some extra parts to keep side walls steady:

 

post-41711-0-98480000-1416386115_thumb.j

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Day 2

framework:

 

post-41711-0-56920000-1416386209_thumb.j

 

cutting sidewalls with router:

 

post-41711-0-70000000-1416386254_thumb.j

 

the first moment I started to realize this is gonna be a horn (!):

 

post-41711-0-87200000-1416386322_thumb.j

 

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Day 2

and this is it! this thing is so big. sounds good already! :rolleyes:  oh I thought it's gonna be at least a week of job but it's 90% done here. I'll go for a trim and then painting.

 

post-41711-0-81360000-1416387470_thumb.j

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I didn't take 5mm of horn edge into consideration and thus the assembly fixture center template was 5mm short in height so the horn throat now is 47mm to 50mm. I'm going to build a new fixture and build the horn again. it's a 1-2 hours job.

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Day 2

the new fixture is much more precise and durable:

 

post-41711-0-54640000-1416395320_thumb.j

 

post-41711-0-64960000-1416395392_thumb.j

 

post-41711-0-43480000-1416395419_thumb.j

End of day 2

Edited by Arash

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Arash just wanted to say thanks for posting your projects.... your work is very impressive in detail and quality...!

miketn

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Day 3

new horns fixed on the new fixture. it's all BB plywood:

 

post-41711-0-98920000-1416453990_thumb.j

 

post-41711-0-64240000-1416454041_thumb.j

 

post-41711-0-12080000-1416454133_thumb.j

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