2397 Horn Project

[GarMan]

Over the weekend, I started on my 2397 clone project. Thanks Mr. Widget for all your postings on specs! I'm sure that anyone who's built one of these will agree that the most difficult part is shaping the vanes, especially the half-vanes on either side. One of these days, I'll get a CNC for the house ... NOT.

I'm not an expert woodworker, just a hobbiest. After an entire afternoon's worth of work, I was able to design and build a jig to carve out the vanes with a laminate router bit.

I'm still trying to figure out how to post photos, but attached is a link to my project album.

http://pg.photos.yahoo.com/ph/lowgc/album?.dir=d8cb&.src=ph&store=&prodid=&.done=http%3a//pg.photos.yahoo.com/ph/lowgc/my_photos

Gar.

[Steve Gonzales]

Simply put: OUTSTANDING!! :applaud:

[yggdrasil]

Way to go.:applaud:

[Ken Pachkowsky]

Very nicely done.:applaud:

[Titanium Dome]

By now you'd think I wouldn't be surprised by the dedication and skill of JBL fans, yet here again I am! Looks great. :applaud:

[Datubie]

Absolutely fabulous!:applaud:

[Mr. Widget]

I'm sure that anyone who's built one of these will agree that the most difficult part is shaping the vanes, especially the half-vanes on either side. One of these days, I'll get a CNC for the house ... NOT.

Your horn project is coming along nicely... you know the vanes are actually tricky with a CNC too. I guess the trickiest part for me was gluing them up and having plenty of glue, but not so much as to have it come squirting out back in the narrow part of the horn where it is difficult to get to all the while maintaining the proper angles and parallelism.:banghead:

Widget

[GarMan]

Widget, I was going to use two small dowels per vane per side to keep them in place during glue-up. Mind if I ask why you didn't go with dowels?

Glue marks aren't that big of a problem if you a) do all your staining/dyeing before glue up, and b) use white instead of yellow wood glue. The white glue dries pretty transparent and only really shows when you try to stain over it.

Gar.

[Mr. Widget]

I didn't use dowels as they are not as strong as using mortises. Most of the factory 2397s I've seen are a bit wobbly... they were doweled. If I didn't have the luxury of the CNC I'd be doweling them myself.

As for staining in advance, I thought about it, but any stain or finish that gets on the glue surfaces radically affects the strength of the glue joint. I am rather picky and wasn't going to accept "pretty transparent". I like knowing that even the parts that you can't see are also nice enough to be seen... I am a nut. I admit it.:)

Widget

[GarMan]

Widget, if you haven't already, move thee away from oil-based stain to water-based aniline dye. Deeper, richer colours and soaks into the wood, even hard maple. Does not leave a film like oil-based stain to affect glue joints. Only problem is that you have to raise the grain and sand first before dyeing.

Aniline Dye at Lee Valley (http://www.leevalley.com/wood/page.aspx?c=1&p=20081&cat=1,190,42996&ap=1)

[Mr. Widget]

I'm an old fart... I first used water and alcohol based aniline dyes at least 15 years ago.;) Unfortunately though they give very clean rich colors they are less light fast than pigmented wiping stains.

Widget

[WWaudio]

You may also consider screwing the vanes in place one one horn half and gluing the vanes (mild application to prevent squirt out as Widget suggested) to the other half upon final assembly. I've found this to be very sturdy and a bit less involved.

[GarMan]

When I started my 2397 project last week, I neglected to read the thread titled "1200Hz Smith Horns for 1" Driver", which contained tonnes of useful info on building a set of these things. I was seriously humbled by the craftsmanship of the builders.

One useful piece of info I got from the thread was the fact that the vanes are sweeps of 25 1/4" radius arcs. My first attempt at the vanes were okay, but not perfect. The template was cut free-hand and some of the irregularities really showed after staining. Over the weekend, I took a second crack at the vanes, taking a very different approach. I built myself a 25 1/4" circle jig and carved out a set of vanes with it. This method is much easier and faster than using a template and laminate router as you can take multiple passes with a plunge router. The vanes all came out smooth and razor sharp.


http://www.audioheritage.org/photopost/data//500/102614_VaneJig2_DblCurve.jpg
More photos can be seen at http://pg.photos.yahoo.com/ph/lowgc/album?.dir=d8cb&.src=ph&store=&prodid=&.done=http%3a//pg.photos.yahoo.com/ph/lowgc/my_photos

Hope to finish the surface next weekend.

Gar.

[Michael Smith]

Gar
When in Rome!
I had problems with the radius so I got a piece of timber being a doubting thomas and did exactly the same thing only with a pencil to see if it worked and hey presto.I have visions of your work shop being a perfect 50'' circle after the router ran amok.
Good stuff
Michael

[bbrown]

Widget,
Why would the vanes tend to be wobbly with dowels? Just my curiosity I guess. I can see how having them mortised would be better, but also more difficult for the woodworking challenged.

Bruce

[Mr. Widget]

Why would the vanes tend to be wobbly with dowels? I would use dowels myself if I didn't have the luxury or maching the parts with my CNC router, but that said as wood expands and contracts over the years dowels become loose. Dining tables with doweled skirts and chairs made with doweled legs tend to get loose to. It is just the nature of wood. Obviously bouncing on a doweled chair will accelerate the process, but typically dowels are not the method of choice for joining wood at 90° angles to each other.

Widget

[GarMan]

I agree that for a piece of furniture like a chair, which experiences high load and lots of movement, dowel joints are not enough. I can also see how JBL's 2397 can have its vanes knocked loose over time if it spends much of its time on the road. Judging from the surface conditions of 2397 I've seen on the used market, they weren't exactly handled with care.

However, most DIY smith horns will end up having a very boring and quiet life at home where glued dowel joints should be sufficient. If fact, I believe that if you have long-grain to long-grain contact between vane and plate, a straight glue-down should be enough for home use.

But then again, if it's worth doing, it's worth doing well. With an engineering background, I see (and have fallen for) the appeal of pushing the boundaries of over-engineering.

It's ironic in some way. The more attention you put into the details of the build, the better you'll treat it in its use, thereby, making all the details less necessary.

gar.