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soundlistening
09-18-2012, 06:53 AM
Hello,
I am amazed at what wooden boat construction involves from a woodworking perspective and would like from you a little help in my endeavour.
I currently would like to make this piece and wonder of anybody would help me undertand the technique that is used to shape the planks to follow the form.
see it here http://www.flickr.com/photos/24668063@N04/7999358016/

Thanks for any help!
Tim

michigangeorge
09-18-2012, 07:08 AM
Simply a bunch of small planks with bevels and angles and such, and a bit of glue :-)

soundlistening
09-18-2012, 07:16 AM
michigangeorge,
Thanks.
The inner and outer curves are not parallel, so planks are twisted. Better to do this from wood or steam?
Thanks for any comments or links to videos or images.
Tim

michigangeorge
09-18-2012, 07:34 AM
Sorry for being so flippant soundlistening. I doubt those short planks were steamed. Picture each side being constructed on a flat surface and then twisted like those paper cutouts you made as a kid. The actual twist is not all that great but I think the curve makes it appear more so. I'm thinking it would be way too labor intensive to do it any other way. What are these to be used for?

soundlistening
09-18-2012, 07:43 AM
Hi,
They are acoustical horns from the 1930's.
So you reckon that the planks that are about 1"x 3" will curve to withour steaming?
That would be good..
Tim

wizbang 13
09-18-2012, 08:38 AM
http://farm9.staticflickr.com/8169/7999358016_f42ec2bf7c_z_d.jpgI see no bending, just bits glued together.
geez, glad I do not need one of these on a boat.

outofthenorm
09-18-2012, 09:15 AM
Assuming they are hollow, do they have to be as smooth on the inside as they are on the outside? If no, this is pretty easy. If yes, then much more challenging.

- Norm

soundlistening
09-18-2012, 09:37 AM
Thanks for all the answers.
Yes they are hollow, added another image here http://www.flickr.com/photos/24668063@N04/7999697054/in/photostream/
And front elevation here that shows they are hollow http://www.flickr.com/photos/24668063@N04/7999701188/in/photostream/
The inside does not need to be rounded, only outside that I guess can be planned.
The large opening at front is 45" x 45".
So the curved part at the back is pretty tight.
I have also made a rough graphic representation:

SMARTINSEN
09-18-2012, 09:48 AM
Like planking the forefoot on a deadrise, individual staves may be roughed out oversize, and shaped to fit. The technique is described and illustrated in Sucher's book on the v-bottom hull, and exemplified in the Draketail thread, which currently active, sits close to the top of the building threads. There is not all that much twist in the individual pieces, relatively more narrow ones used in the areas of the most curvature.

Mrleft8
09-18-2012, 10:36 AM
A bit like whittling a propeller for a model airplane, but different. The shape is actually not as complex as it appears, if you look at it as a series of straight cuts on different planes.... I'll try to illustrate my thesis with pictures rather than words in a few hours, as I have to find some photographs, scan them, upload them, and post them, and I have other things to do today as well..... But I will be back! :D

David G
09-18-2012, 11:16 AM
If you want more technical detail look up 'coopering' techniques.

Oldad
09-18-2012, 01:11 PM
I would make those from bendy plywood, piece of cake, see thread on wacky wood

Eddiebou
09-18-2012, 02:39 PM
Yeah, that's a tricky thing you got there..... I understand it. I can visualize how it's built. But I'm glad I don't have to build one today... I'm really glad I don't have to build 2 exactly alike. And I've built some pretty odd shaped things. I'm thinking you could make a pattern of it's shape from aluminun coil stock and some thin plywood. Work from a centerline. Maybe make the top and bottom oversized, then trim? Maybe use gauze or tape the backsides together, of course the bevels will be different as you continue up the spiral. I guess you could loft it in side plan to get the bevels. Nice thing about bevels is they can slip past each other and make up for thickness differences. It would be nice if there was a rabbet for the boards to land on. Are there any nails in it? I can see fairing it all out after it's glued up- 36 grit disk on soft pad, no problem.
Let us know how it turns out. Take photos along the way.:confused:

outofthenorm
09-18-2012, 04:25 PM
I think I would build a form or jig in the shape of the horizontal surfaces - one for the top, one for the bottom. I would use some bendy ply for surfaces.

Then I would fit and glue together the top and bottom faces, beveling as needed for each piece, making up full width blanks.

Then I would loft the proper shapes onto the blanks and cut them out with a jig saw. That gives you tops and bottoms

I would then make up another jig to hold the top and bottom in their correct relative positions and proceed to cooper-build the sides one piece at a time. Any bevels needed at the join could be cut as you go.

It looks like the sides overlap the top and bottom, so I would leave the pieces long and trim with a router and a guide bit once it's all done.

Glue and long nails might be enough for the connections, but it could be easily reinforced with a bolt and cross-dowel through every third or fourth side piece.

But that's just me:D

Norm

Mrleft8
09-18-2012, 04:46 PM
It's not that complex..... I'm headed out to the barn to take pictures.....

LivingTheDream
09-18-2012, 05:41 PM
If this is used as an acoustic horn, I think having the INSIDE true and smooth would be paramount. Sound waves are like water, they bounce off of any surface that obstructs their flow. The shape of this thing looks like it is set up to be a natural amplifier, so any rough or sharp edges would dampen that effect and could produce the dreaded 'canceling wave', rendering them useless.

Gerarddm
09-18-2012, 10:58 PM
Pure Timber.

http://www.flutedbeams.com/magazinearticles.html

Soundman67
09-19-2012, 02:56 PM
I would just make a template of each panel. This is a real good place to use Stictch and Glue technique. A couple of cross braces in the mouth to make sure its square and bend in layers of 1/4" ply until you get the thickness you need. These horns should reach nicely down to about 100hz so you could even fill the panels with lead shot and epoxy to make them less resonant. What driver is meant to go onto these? If you want really efficient Mid/bass look at the Adamson 10"mid driver. Its 110db Spl.

Mrleft8
09-19-2012, 05:41 PM
Sorry..... Power's been out..... I'll try to upload pics tonight....

Terry Haines
09-19-2012, 10:41 PM
It's strip-built like many kayaks, but I can't imagine how it was assembled . . .

Mrleft8
09-20-2012, 08:42 AM
Terrible pictures, but I didn't think that I'd be trying to illustrate a construction technique when I took them....

http://i358.photobucket.com/albums/oo23/Mrleft8/morevarious_zpse564e32b.jpg

Mrleft8
09-20-2012, 08:50 AM
Each facet of the base is made from 5 layers of 1/8" baltic birch ply, 8" wide by 30" long (+-) bent over a 52" radius form, and glued with Titebond yellow glue.
http://i358.photobucket.com/albums/oo23/Mrleft8/morevarious012_zpsb76f4b08.jpg

Mrleft8
09-20-2012, 08:53 AM
http://i358.photobucket.com/albums/oo23/Mrleft8/morevarious009_zps95f4f3cf.jpg

http://i358.photobucket.com/albums/oo23/Mrleft8/morevarious008_zpsfe8f9b86.jpg

Mrleft8
09-20-2012, 08:59 AM
What appears at first glance to be a nightmarish rolling bevel the entire length of both edges of each stave, is in fact a simple 22 1/2 degree bevel cut in a straight line on a table saw.

http://i358.photobucket.com/albums/oo23/Mrleft8/morevarious016_zpsfadebf6f.jpg

http://i358.photobucket.com/albums/oo23/Mrleft8/morevarious015_zps18397047.jpg

http://i358.photobucket.com/albums/oo23/Mrleft8/morevarious013_zpsa7a4f867.jpg

Mrleft8
09-21-2012, 05:59 PM
Wow..... No comments?..... No questions?...... I'll see if I can dig up some better pictures of the whole thing.... I thought it was pretty interesting, and it was me who did it!

Jazzman
09-21-2012, 06:15 PM
I think LivingTheDream has a point. Are you going to use them as an acoustic device, or just a pretty shape?
At first i couldn't get the perspective right- I thought they might be some kind of funky skateboard ramp!

John How
09-21-2012, 10:58 PM
I hope they sound as good as they look.

Mrleft8
09-22-2012, 09:25 AM
At any given point, the cross section of the horn is square. Essentially you have a square sectioned pyramid. It's fairly straight forward to build a pyramid. Now divid your pyramid into (10) horizontal sections and remove (10)% of the material from the (left) side of each section, and taper the sections to fair. Now you have (10) sections of truncated pyramid with nonparallel edges (I really should not have slept through 18 years of math class).
Now reassemble the sections and you have a pyramid which resembles a square dragon's tooth. Now pretend that you're making wine casks from properly seasoned White Oak staves, which must look like this dragon's tooth, but be smoothly rounded, not a series of flats....
See? It's really quite easy. A series of simple angled cuts. I think that if I were making it, I'd use bending plywood or laminated veneers instead of solid wood staves as shown, but that's because I'm more comfortable working with that material.

Terry Haines
09-22-2012, 10:07 AM
Not quite that simple. When you remove material from one side of each section the resulting opening is no longer square, because of the taper of the pyramid. Because the next section it is supposed to be join ed to is still square they will not fit. The pyramid needs to be divided into many more sections - an infinite number in theory - to get around this problem.

Mrleft8
09-22-2012, 03:45 PM
Not quite that simple. When you remove material from one side of each section the resulting opening is no longer square, because of the taper of the pyramid. Because the next section it is supposed to be join ed to is still square they will not fit. The pyramid needs to be divided into many more sections - an infinite number in theory - to get around this problem.
Of course it is. Square remains square.

Terry Haines
09-22-2012, 07:02 PM
Of course it is. Square remains square.

If it's cut straight across, yes, but not when it's cut on a slant.

A square tube cut on a slant results in a rectangle not a square. A circular pyramid (cone) cut on a slant results in an ellipse, a hyperbola or a parabola - depending on the angle of the cut, but it's only a circle if the cut is straight across. For a square base pyramid the result will be a trapezoid.

David G
09-22-2012, 08:18 PM
Lefty's technique is, indeed, what I'd do if I were merely trying to create that shape - to be painted for furniture or somesuch.

Being an acoustic device, I'd image that the solid timber bit is important. Not only that, but the right species, and the right thickness.

Have you researched coopering techniques yet?

Mrleft8
09-22-2012, 09:23 PM
If it's cut straight across, yes, but not when it's cut on a slant.

A square tube cut on a slant results in a rectangle not a square. A circular pyramid (cone) cut on a slant results in an ellipse, a hyperbola or a parabola - depending on the angle of the cut, but it's only a circle if the cut is straight across. For a square base pyramid the result will be a trapezoid.

That's the word I was thinking of that I couldn't remember!
Yes, you do end up with a trapazoidal opening in the cut, but when attached to it's mating piece, that direct radial section remains square as it crosses the tangential cut line. (I think I got those terms right..... Maybe backwards....)

Terry Haines
09-22-2012, 11:26 PM
I must admit I haven't figured out what happens at the joint or as the process continues along the pyramid! I need to put in a few hours at origami . . .

Terry Haines
01-03-2013, 06:30 PM
The link in the original post has been changed, I can only find this image which does not show construction -

http://www.flickr.com/photos/24668063@N04/7999716081/in/photostream (http://www.flickr.com/photos/24668063@N04/7999716081/in/photostream)