Enclosure w/ curved sides, need your help

[MITMechE]

Hello Folks,
I'm making 4 new boxes, 2 floorstanders and 2 bookshelves. Lute-like shape similar to the sonus fabers or lots of the curved designs we've seen around here lately.

I've built the skeletons for each speaker, and only need to laminate multiple layers of thin mdf on the sides to form the curves. Started with 1/8" mdf on one of the bookshelves and I'm having a heck of a time with it, at this pace I'll be done sometime next year. I've got three layers on only one side.

My process involves nailing down each little bit as I bend over the speaker and then clamping with some luggage tiedowns till it dries. This process is, as you can imagine, very slow.

So here are my questions:
Is there a better method?
Should I use construction adhesive or something else instead of yellow carpenters glue to glue the layers? (I'm worried I'm not getting good contact between subsequent layers w/ the carpenters glue)
Will my enclosures be rigid enough with just 2 layers of flexi-plywood or something similar that's easier to bend.

I'm having a hard time with the 1/8 inch mdf on the bookshelves, and I was planning on using 1/4 inch mdf on the floorstanders.

[navin]

when i built the cabinet shown below i found that mdf was tougher to bend than ply. i used 3 layers of 4mm marine ply and alternated that with 3 layers on 3mm MDF.

to do this i first built a frame. each layer was laid on the frame. each subsequent layer was nailed and glued to the earlier layers and kept in place by over a dozen c clamps to dry over night. I managed 1 layer per day. cust lay, glue, clamp, nail. and i needed help.

took me 24 days + to complete 4 sides.

[mike_biddulph]

I did this by making the curved sides first by laminating 3 layers of 6 mm mdf to gether all in one go. I used a curved form and made clamps from 2" by 2" and studding, to clamp the edges of the laminates down onto the form.

[mike_biddulph]

Each side was left overnight to dry and then I cut the top and bottoms to a matching profile with a router and mounted them on a stongback, a plank that secured the ends aligned and the correct distance apart, the sides were then glued onto the ends in the jig and the strong back then formed a reference platform for the router to trim the front and back flat. The dowels in the picture are used both to align the ends on the strongback and to locate the front and rear faces.

[mike_biddulph]

The brace can then be clipped into the body and glued into place before fitting the bitumen damping and foam, the panel, behind the speaker is the front before cutting the holes for the drive units. I made it this way as a trial run, using scrap I had lying about, but I would say that 6 mm mdf is too thick for this, I dont feel that the speakers are long term stable and will start to delaminate. I am now designing a more advanced construction, to be laminated from 3 mm ply to get a home brew version of gridded bracing inside the curved panels, for my next project, which is currently a mix of a faber style body with the EVEII units and XO as a starting point.

Hope the method seems clear.

mike.

[officeboy]

I have a curved sided project going now too.

I would suggest you not use thin MDF.. It’s much stiffer then I would have guessed.

Just getting started on layer 2., but i need to prebend the MDF for about a day or else it'll crack in 1/2 when i go to attach it.

http://home.comcast.net/~0fficeboy/D8/index.html

[mike_biddulph]

for completeness, the finished object, the crossover is still being tweaked but will be mounted externally at the back of the base

[Mos Fetish]

Hey, you guys want to get in touch with Andy G so he can post your pics on his curved sides loudspeaker page. Pictures say a thousand words and it's all helpful for the beginner.

For myself, I'm using the translamination approach, that is, individual ribs cut on a CNC router and then laminated together in a multilayer stack with integral bracing and dividers.

Mos

[navin]

The translam approach has 2 disadvantages.

1. u must have access to a nice machine to cut all the laminate together.
2. it wastes a lot of wood.

in my project wood wastage was less than 5%.

the abinet is about 16" deep (48"/3). 3 layers of MDF per side. 3 layers of Ply per side.

a 4'x8' sheet gave me 2 sides so 1 sheet of ply and 1 sheet of MDF made one speaker.

the wastage i had was mostly due t the holes cut in the braces.

[MITMechE]

I agree Navin, lots of waste and lots of time to make each layer if you don't have access to a cnc router.

I used my departments small laser cutter and cut an acrylic template from my CAD model for each of the frame members. There are six frame members per side, so 12 total. Rough cut each frame member then use the template and router to make 12 identical copies. For the translam approach I'd need 122 layers and 21 4 x 8 sheets of mdf.

I've tossed the idea of bent mdf. A combination of: borrowing my brother's pneumatic brad nailer and bending plywood, made my project move a lot faster. The bending plywood (aka wacky wood) is 3/8" thick, two layers glued together with the underlying frame seems sufficiently rigid.