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Discussion Starter · #1 ·
I'm doing a small set of bookshelves, .5 cu.ft. and wanted to do a curved sided cabinet.

I've done some basic woodworking and casework, but have never attempted anything like this.

From the reading I have done, I can use thin mdf, or bendy ply. I had though of using thin (say 1/8 or 1/4) BB, but nobody seems to do this.

I was figuring on 3 or 4 vertical frame pieces out of ply to define the shape and a couple of horizontals to hold everything in shape. I need to work out the size and work up a template.

I've searched forums and found a few threads, but if any of you have done curved sided cabs I would appreciate your input.
 

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Some people have used 3/4" BB and cut slots 1/2" deep every inch or so apart. This makes it somewhat bendable.
 

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Discussion Starter · #3 ·
I've seen that, but I wonder how this affects cabinet resonance.

I'm going to talk to a local specialty wood products company about bending thin BB ply. I'm surprised this is not done, but there may be good reasons.
 

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Discussion Starter · #4 ·
I'm also looking for a reality check on costs. My alternative is using a pre-built cabinet at about $250 by the time you add taxes and shipping.

I figured I could do this for aroung $100 in materials including a nice veneer of my choosing. Does that seem reasonable?
 

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Kerfing 3/4" MDF or ply is better than using thin bendable plywood for resonance issues IMO. In either case, to deaden the curved sides after bending try using fiberglass resin inside the enclosure.
 

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Discussion Starter · #6 ·
OK, found the thread I was looking for on using 1/8" bb ply. Wohoooo!!!

Dead Sexy!!



The original thread is here. Now I need to figure out rough dimensions and do some costing.
 

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I would not use that thin of wood...ever. You can also do layers of 1/4 inch, one on top of each other to get the correct thickness.
Yep I forgot about doing the same thing with MDF, that works also:T
 

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Discussion Starter · #9 ·
I would not use that thin of wood...ever.
If you build up layers to the appropriate thickness, why not?? Thats all ply is, thin layers of wood glued together.

1/4 would be a more desirable option because it involves less work. I don't know how thick I can go with this method. The big question I have is of band clamps will provide enough pressure over the entire sheet to properly laminate sheets.

I know I could use MDF, but ply seems to be the preferred choice when price is not an issue.

I could go real fancy and use both mdf and ply and do a constrained layer cabinet, but I don't know that I really need to go that far. I may just explore that option for fun though.
 

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Discussion Starter · #10 ·
3/4" MDF and kerf it will be the best. the walls will flex if too thin. Kerfing Isn't hard to do.
Maybe I didn't explain myself very well. I'm looking to build up to a 1/2" to 3/4" thickness here.

It seems to me laminated 3/4" anything is going to be better than the same material kerfed unless there is a structurally sound way to re-bond the kerfed material. Yes? No?

There are probably many ways to skin this cat since labour costs are irrelevant.
 

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LOL. I think doing layer's would work out well. I just looked at how he did it and I think That would work out pretty well. Cool looking design. I say go for it and let us know how it come's out. building it yourself and staining the wood your own color will be rewarding. Just make sure and do internal bracing and you'll be good to go.
 

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Discussion Starter · #13 ·
Played with Sketchup for a bit tonight and came up with this:



Add the front baffle and the cabinet back and I should have a good frame to wrap the side walls onto. I figure I can set the two curved frame pieces into dados in the front and back pieces to help square things up and make assembly a little easier.
 

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Hi Fred

I can see that there are quite a few opinions being posted. So I'll add mine to the list. Go with your idea. Use the 1/8th" ply in what ever build up thickness you care to do. IT will become as stiff as all get up when it is cured. It will work like a charm. The clamping idea from the thread you sited is also quite good. You will need more clamps by the way. On a box your size you can either make cauls and use regular clamps or clamp it with band clamps. In a pinch I have used the strapping that holds large bundles of lumber together. But that requires a bit of skill.

And by the way most of my career as a cabinet maker has been in doing the weird and wacky world of curved work. Been at it for 23 years. Done some real neat stuff. I have quite a few sheets of 1/8th" baltic birch plywood in my storage shed behind my shop for just such a project. But the bends will be a smidge more interesting. :bigsmile:

The kerf cut mdf will work as well but it will not be as stiff. So will the kerf cut plywood. But depending on the plywood you will cut most of the way through before you can get it to bend.

Mark
 

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...
It seems to me laminated 3/4" anything is going to be better than the same material kerfed unless there is a structurally sound way to re-bond the kerfed material.
...
You missed the post telling you to coat the kerfed area with fiberglass resin after the bend is set, to fill in all the kerfs and eliminate any potential for structural weakness or resonance. Kerfed MDF with a nice veneer is the cheap way to go (depending on the veneer) but layered BB has a certain visceral appeal.

Have fun,
Frank
 

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If you build up layers to the appropriate thickness, why not??
Building up is fine. 3/4" being minimum. My point is not to have a 1/8 thickness for the walls...
For the baffle use at least 1.5" thick and using inner layer of MDF and outer layer BB works quite well:T
 

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Discussion Starter · #17 ·
Frank. I did see that. Having worked with fiberglass a little I'm not a big fan of using it unless you have a well vented place to work. I would also be concerned about flowing the resin into each curf properly and voids.

It may end up not being an issue, but it seems to me that laminating will be easier to manage properly.

Hi Mark. I appreciate your comments as I know you do this stuff for a living. I'll probably have more questions as I get closer to the build
 

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For the baffle use at least 1.5" thick and using inner layer of MDF and outer layer BB works quite well.
Hi Fred

Michael's idea is good. One of the things that a custom box can do much better than a bought box is not make any sound of it's own if it is properly done. Your constrained layer sides will still resonate but it will be quite high up in frequency. A layer of ice and water sheild will dampen that out. But the front baffle is where all the goings on takes place. If you provide a firm foundation for the launch of your music it will indeed sound cleaner. In the midrange for sure and even in the upper bass. The best cabinets I do have a 2" thick front baffle. For the size your considering 1 1/2" is plenty. Personally I would make a sandwich of Baltic birch and MDF or whatever you have on hand. It will distribute resonances better if you use different materials. I basically mean that your box will vibrate less if you have a heavy front baffle.

Mark

Mark
 

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Discussion Starter · #19 ·
One of the things that a custom box can do much better than a bought box is not make any sound of it's own if it is properly done.
That was one of several reasons for going with a custom cabinet. Unless I use an appropriate glue, I don't think what I am doing qualifies for constrained layer. I need to figure this out as it might just be worth while trying to do a constrained layer design since I'm doing the curved sides already.

Your constrained layer sides will still resonate but it will be quite high up in frequency.
Hmm, what must one do to stop the cabinet from resonating?

Actually, I wonder how much the tweeter will put out into the cabinet in resonance since it is essentially sealed driver. If that is true, I would want to push the cabinet's resonant frequency up above the crossover point. I think that will be in the 2-3 Khz area for this woofer.
 
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