bending wood

[navin]

hi guys,

one more problem....
i am trying to build a speaker using curved sides a la Wilson Benech Act Two and Sonus Faber Amati see link below

http://www.hifi-notes.com/sonusfaber...brikage-nl.htm

I have built the bracing (actually I cut out 18mm MDF in the shape I wanted) and tried to bedn 8mm and 6mm MDF sheet but it did not work. 4mm MDF sheet works but to get a 25mm thick cabinet one would need 6 sheets of 4mm and that might end up lookng like plywood and worse still actine like plywood.

I have 6 18mm MDF braces per cabinet. The top and bottom are 30mm MDF.

1. how does one bend MDF?
2. is there an alternative to bending MDF?

Regards
Navin

[navin]

http://www.wilson-benesch.com/acttwols.htm

in case you need to see what I am trying to make.

[Andy G]

the 4mm mdf is probably the best way to go.

If you have a look at "Windswept" and "Tulip" on my web site, you will see some eg's of what can be done. (they actually use 3mm mdf)

ok, there is the problem with the edge showing, but there must be a way around that, you are not leaving it raw anyway!!

as to "sounding" like ply, i can assure you that it will not !!!
If you laminated the layers with pva type glue, spread on evenly over the whole of both surfaces using a paint brush, you be amazed at just how NON-resonant they become very quickly !! The 4.5" Tulip uses only 3 layers of 3mm mdf, and if you tap the outside of it, all you get is the dull thud of much thicker flat mdf.

Go with the 4mm mdf, try it after you have say 4 layers on, and see what you think !! you can always add the extra later if you really feel you need to.

Oh !! and have fun, it ain't easy !!!

AG

[PedroPO]

I'm not sure if this can help at all, but once I've seen a guy doing curve chairs with plywood for a boat that he was building.

his method was the following:

- make a steel frame with the shape of the bent wood final.

-insert the strait plywood panel in the steel frame and squeez it.

- the frame was filled with water. I dunno if it is on the beginnig or the end of the process.

[Andy G]

... I suspect that the "bendablity" of mdf is proportional to the square of the thickness, so 3mm is about twice as bendable as 4mm,

don't try to to bend 18mm !!

[Andy G]

DO NOT, under any circumstances, soak the mfd !!!

[FrankDIY]

I suggest to cut the MDF like this:

Inside

|xx|__|xx|__|xx|__|xx|__|xx|__|xx|__|xx|
|xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|

Outside

You can use a saw with the correct depth or a router.
Try several depths and widths to see which one is the best. I have used this idea with plywood for another project (not a speaker box) and it worked fine. It should work with MDF.

[roddyama]

I would try ply wood over MDF. I fear that the MDF will try to separate as you glue more on layers. It is not very strong in that way. There are layers in the structure of MDF that are not as strong as a glue bond.

Take a look at this site. These guys make Hedlund horn copies by bending and bonding layers of plywood on a form. The last layer is the venier. Beautiful work!
http://hornet.hi-fi.hr/Pics.htm
Select "Details from Production"

Just a note: try to find marine or aircraft grade, void free plywood. That should keep you from getting any seams or holes.

As Andy says, "...have fun, it ain't easy !!!"
Rodd Yamas***a

[Two Moons]

Navin,

I am going to make some speakers like the ones you have planned. My inspiration were the Sonus speakers you provided the link to. Laminating multiple layers of plywood or thin MDF will give you tremendous strength, especially if bent. Search the knowledge base at www.woodweb.com and maybe ask questions in a forum. There are many experienced woodworkers there who have a lot of experience with the bending of many types of wood.

Good luck with your project and post pictures of it when ready. I'd like to see how someone elses turns out before I get my feet wet.

Dave

[Variac]

At a plywood store or good home fixup place they have 4x8 panels of stuff that is 1/2 " particle board ripped about every 1/4" as Francois described. BUT it is glued to a piece of high quality birch veneer (on one side only)

Amazing stuff- it will bend to a 4" radius. Only in one direction
I was thinking about making an open baffle with 4" radius edges
on the sides by filling the cracks with glue. That's a lot of glue though! I think it will be very rigid when it dries(if ever)
It would be best to use glue with fibers mixed in-maybe just sawdust. Best to use ribs to set the shape first-they could be removed if necessary.

You mentioned that many layers would be like plywood-I don't think so. But, even plywood in that shape would be fine I'll bet.

Look at the Sonus fabers-they are made from solid wood, which is supposed to be bad, but the shape makes them work I'll bet.