# Bending baltic birch



## Svendsen (Apr 21, 2012)

I everyone

I'm new here, also new to woodworking, and I'm hoping you could help me a bit.

I'm thinking of building a subwoofercabinet at 20"x20"x20" in Baltic birch 3/4" with a double layer on the front - and the thing is I would like it to have curved sides.

I would like to assemble it without any screews just with clamps or something similar - I would like the sides to bendt somewhere between 3-6" Can this be done - and how?

Thanks

Best regards

Svendsen


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## Svendsen (Apr 21, 2012)

I mean Baltic Birch plywood


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## dmh (Sep 18, 2010)

I'm not real sure how tight you want to bend it but it can be done (to a point) with a series of relief cuts on the back side of the ply.

Assemble with a rabbit or dado joint and glue.


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## Svendsen (Apr 21, 2012)

dmh said:


> I'm not real sure how tight you want to bend it but it can be done (to a point) with a series of relief cuts on the back side of the ply.
> 
> Assemble with a rabbit or dado joint and glue.


Well i has to be really strong because of pressure created by the massive woofer.


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## Svendsen (Apr 21, 2012)

I've seen these photos, and it looks quilte impressive


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## dmh (Sep 18, 2010)

Is that what your wanting to build? If not do you have a picture of what your wanting to do?

The curve in that picture is not nearly as tight as I thought you were wanting.


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## cabinetman (Jul 5, 2007)

For tighter curves the saw kerfs would be closer together and deeper. For gradual curves the kerfs further apart, and more shallow. Experiment with samples first for the type of curve. The kerf side can be bondoed in to create a very solid panel.










 







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## Steve Neul (Sep 2, 2011)

I don't think baltic birch plywood is a good choice for rounded sides. It comes in so many layers, to kerf the back like DMH has illustrated you would have to cut nearly through it and each cut would show. Since you don't like the idea of kerfing the back anyway you might use bendable plywood, sometimes called benderboard and normally comes in sheets 3/8" thick. With normal plywood the direction of the grain is alternated with each layer to make it ridgid and stronger. With the benderboard the wood is soft and has the grain running the same direction. This plywood bends almost like rubber and when you laminate two or more layers together becomes pretty strong. The problem is it doesn't come with the finish veneer. You would have to veneer over the outside when you get the shape you like.


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## cabinetman (Jul 5, 2007)

Steve Neul said:


> I don't think baltic birch plywood is a good choice for rounded sides. It comes in so many layers, to kerf the back like DMH has illustrated you would have to cut nearly through it and each cut would show. Since you don't like the idea of kerfing the back anyway you might use bendable plywood, sometimes called benderboard and normally comes in sheets 3/8" thick. With normal plywood the direction of the grain is alternated with each layer to make it ridgid and stronger. With the benderboard the wood is soft and has the grain running the same direction. This plywood bends almost like rubber and when you laminate two or more layers together becomes pretty strong. The problem is it doesn't come with the finish veneer. You would have to veneer over the outside when you get the shape you like.



Actually BB works very well for bending/kerfing, as the face is very smooth, and there's no voids. What will determine the smoothness of the face of the curve is how deep and the proximity of the kerfs to eachother.

Bending ply works well too, and it comes in different thicknesses. It has to be backed up with forms of some sort to create a fairly rigid panel. Two layers glued together do well for providing some rigidity.










 







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## Svendsen (Apr 21, 2012)

So if I just try to bend and glue a 3/4" piece of bb plywood, like what I Think I see in this photo, I would expect it to crack


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## Steve Neul (Sep 2, 2011)

cabinetman said:


> Actually BB works very well for bending/kerfing, as the face is very smooth, and there's no voids. What will determine the smoothness of the face of the curve is how deep and the proximity of the kerfs to eachother.
> 
> Bending ply works well too, and it comes in different thicknesses. It has to be backed up with forms of some sort to create a fairly rigid panel. Two layers glued together do well for providing some rigidity.
> 
> ...


The problem I've had bending baltic is the veneers are so thin you have to make the kerfs closer to the surface than seven ply. Then when you bend it the saw kerfs show in the surface veneer. More than likely with Svendsen's speakers he will be making a more gentle bend to where that may not be a problem anyway. Without his plans I couldn't make that assumption.


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## Steve Neul (Sep 2, 2011)

Svendsen said:


> So if I just try to bend and glue a 3/4" piece of bb plywood, like what I Think I see in this photo, I would expect it to crack


No. with that gentle a radius it would bend fine. You probably shouldn't need to run the kerfs more than half way through.


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## cabinetman (Jul 5, 2007)

Svendsen said:


> So if I just try to bend and glue a 3/4" piece of bb plywood, like what I Think I see in this photo, I would expect it to crack


It would crack if: The kerfs aren't deep enough, or too far apart.

It would show flats if: The same as above.









 





 
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## dmh (Sep 18, 2010)

Svendsen, I might be wrong but from the looks of it that curve was done with laminated sheets rather than plywood that you would find in a store.

I think it would be more work but have a look at this thread for an idea of how its done.


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## Dave66 (Apr 6, 2012)

I'm building a couple of speaker boxes for a really serious audiophile and the learning curve has been fascinating.

One thing I've learned is that the box material needs to have a very uniform density with no voids. Voids and variations in density can really screw up the acoustical response of the box. My boxes are 3/4" MDF core maple with 3/4" MDF internal baffles/structural bracing.

If I were trying for a curved front, I wouldn't just make a bunch of kerf cuts so I could bend the piece. That would just create a bunch of voids that might wreck the acoustics.

I think that I would make a jig in the shape I need; make my kerf cuts in MDF core ply; fill the cuts with a slow setting wood filler, and quickly clamp the piece to my jig. Most of the filler should squeeze out leaving the kerfs filled. When the filler has dried, the piece should have the curve you want. You'll need to scrape or sand off the squeezed out filler.

One problem I see with curving the front would be installing the driver. Is it curved too?


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## Svendsen (Apr 21, 2012)

To everybody - thanks for advice - now I know that I just can't bend the plywood without kerf cuts - a lot easier and chefer to find out this way




Dave66 said:


> I think that I would make a jig in the shape I need; make my kerf cuts in MDF core ply; fill the cuts with a slow setting wood filler, and quickly clamp the piece to my jig. Most of the filler should squeeze out leaving the kerfs filled. When the filler has dried, the piece should have the curve you want. You'll need to scrape or sand off the squeezed out filler.
> 
> One problem I see with curving the front would be installing the driver. Is it curved too?


...and I Think I'm gong to go with Daves advice about the slow setting wood filler - and it's online the sides I'd like to curve, the front is another level of difficult.

Svendsen


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