Something Stirs in the Workshop

[vinylnvalves]

Thought I would plagiarise Mark's thread, as this is a long project ( hopefully not as long as Marks )

I am building a new pair of midrange horns, but this time I have got for an elliptical one to get better vertical integration. I have had the definition of the horns for a number of years curtesy of JMLC who gave me a spreadsheet. After a few years of wondering how to make them, I decided to CNC them. So about 18 months ago I started building a CNC router, with a bed big enough to machine the 200hz horns. After commissioning the machine and learning how to write Gcode, I started the horns.....

Decided to machine them in slices and glue them together, using a watermark aproach machining in 1mm steps for the inner and 2mm steps for the outer. Here's some pictures of how far I have got .....

[steve s]

Very impressive Steve... building a cnc router too, wow !!

[vinylnvalves]

Thanks Steve, The aim is to have them finished for the next Owston meet. The next sections start to get big and have a re-enterant feature so there will be some hand shaping too as I only have 3 axis. Widest point is about 800mm, so reckon I will need a couple of sheets more of birch ply.

[Dave the bass]

Phwwwwwwwwworrrrrrraraaaaa(h)!

Bonkers and ace at the same time. Respect.

[IslandPink]

Nice one !
I wondered what you were up to.
Something good about the title too....
Reminds me I must talk to Chris V about how his mate down South is doing with some elliptical JMLC's , they are probably a bit smaller , maybe 350 or 400Hz.

[vinylnvalves]

Done a bit more machining and gluing. On the final leg now. Just got the ears to do. Had to get into more complex machining to get the re-entering features. Changed to a ball nose cutter which gives a better surface finish.

[IslandPink]

Now you've got me confused. What's with the ears ?

[vinylnvalves]

The bits that go on the top and bottom of the horn, another 250mm of material to add.

[vinylnvalves]

Something like this...

5536689A-C3C2-48A7-ACFB-6C12395CEC89.jpeg (27.78 KiB) Viewed 56789 times

[IslandPink]

Ah yes, of course. Makes more sense when the full top/bottom flanges are there.
What Hz is the little one ?
Wondering about trying the Radian 745Be on a small elliptical some time, around 700Hz to 1000Hz exp.

[vinylnvalves]

Finished matching and gluing all the sections together now. Next step involves a Japanese rasp... got to decide if I want wood finish of a lacquered finish, if later need to use glass fibre tissue and gel coat.

Was hoping to get a room at the Scalford show but out of luck will have to audition them at Owston instead,

[Dave the bass]

Phwoaaaaaaaaaaaaaar (etc!).

[Ray P]

Outstanding work!

...if later need to use glass fibre tissue and gel coat.

If you're talking about polyester gel coat I wouldn't go there; it's quite viscous and it'll be really hard to get a smooth finish. Personally I would use some glass or carbon tissue wetted out with low viscosity epoxy, something like this;

https://www.bucks-composites.com/produc ... -cure-time

I've use it for finishing model boat hulls (and mould plugs) and if you remove all the excess resin you can get a paint like finish.

[vinylnvalves]

Thanks for the info on the finishing epoxy, yes this probably what I meant, coloured gel goats do allow you to sand and buff it to a mirror finish though, without needing to spray it. Have some bits of tissue and epoxy left over that I might practice with first.

[Mike H]

Good lord.