"pre-bending" lamination pieces by soaking / bending them first?

[Tom Lindsay]

Hi,

I am in the process of building a small half-round table out of cherry, and am looking for some suggestions on bending the apron for the table top. I created a form (both "male and female" sides), and lined it with plywood to make an even flat surface. To make it easier to get the plywood shaped to apply to the form, I soaked it in water first and then inserted it in the form overnight to "pre-bend" it before fastening it to the form.

I was thinking of doing the same with the 1/8" strips of cherry that I plan on using for the lamination (built up from 5-6 strips). I would soak them and "pre-bend" them overnight, then remove them and let them dry before doing the actual glue-up. I figure this may make the glue-up easier, and might help reduce any spring-back.

Is there some flaw in my logic here? Thanks in advance!

[Doug Shepard]

I did exactly that when I made a cherry half moon table. I got a disposable plastic tray used for wallpapering, filled it with hot water and soaked the whole stack for about 30 minutes. Then pulled the stack out, wiped each piece off well, then stuck the stack in the bending forms. I just let mine sit for about a week though. I got little if any springback but i dont know how much you can attribute to the pre-soaking. It does help to have some of the bend already in the pieces when you atart doing the real glue-up though. Just keep track of the stack order. You've got a couple opportunities to mix up the order and get grain goofs, both during the pre-clamping and the final glue-up.

[Gary Muto]

Great idea. I've wanted to do a curved front table and the idea of bending (even laminations) has been intimidating. I struggle with getting things straight let alone curved.

[Doug Shepard]

Forgot to post a link on the earlier reply but here's the victim of my pre-soaking/bending.
http://www.sawmillcreek.org/showthread.php?t=15693

[Bill Arnold]

I've done a number of bentwood laminations using my vacuum press and have never soaked the pieces. I generally use pieces I've milled to 1/8" thick and have done as many as nine layers. I use plastic resin glue for laminations because there's ample open time to work with the assembly and it dries hard enough that there is usually no springback.

[Frank Drew]

As long as the grain doesn't raise so much or the wood move enough to interfere with your gluing, this sounds like a good idea; like Bill, though, I've never done it and have good results with my laminations.

Another way to do curved work is to bricklay the shape then veneer; low tech, and works well.

[Tom Lindsay]

All,

Thanks much for the feedback. I'll watch to insure I keep the order during the glue-up, and will see if I have to knock down any grain before gluing.

And Doug, that is a beautiful table!

[Larry Edgerton]

Something I have figured out with prebending is to leave the stock at least 6" longer than needed as the last bit will tend to take less of a curve. Cut this part off when assembling. I always make my forms that much longer.

[Bill Arnold]

Something I have figured out with prebending is to leave the stock at least 6" longer than needed as the last bit will tend to take less of a curve. Cut this part off when assembling. I always make my forms that much longer.
Six inches is a lot of material to waste. I make my forms a few inches longer than the length of the finished product but the working pieces are only slightly longer than needed -- maybe 1/2" to 1". For instance, on my compass table (below), the apron was formed in four pieces, each being a lamination of nine layers. The total length of a segment was determined by the length of the outside of the curve. I added an inch to that length and cut all pieces accordingly. Using plastic resin glue and my vacuum press meant I had no springback along the curve.

http://bbarnold.com/images/tbl_cmps1_a.jpg

[Brian Penning]

Hi,

I am in the process of building a small half-round table out of cherry, and am looking for some suggestions on bending the apron for the table top. I created a form (both "male and female" sides), and lined it with plywood to make an even flat surface. To make it easier to get the plywood shaped to apply to the form, I soaked it in water first and then inserted it in the form overnight to "pre-bend" it before fastening it to the form.

I was thinking of doing the same with the 1/8" strips of cherry that I plan on using for the lamination (built up from 5-6 strips). I would soak them and "pre-bend" them overnight, then remove them and let them dry before doing the actual glue-up. I figure this may make the glue-up easier, and might help reduce any spring-back.

Is there some flaw in my logic here? Thanks in advance!

Based on my experience in doing many many bent laminations there's no point in soaking the strips if they're only 1/8" -you'll be able to bend and glue that up easily to a form. You won't get all that much spring-back either.

Can I assume you've taken into account the the material thickness for making 2 different radius's(sp?) for the male and female forms?

I've also found that I get better laminations if I cut one side of the form into segments like so...

http://i47.photobucket.com/albums/f193/Bri68/Building%20a%20rocker/IMG_2628.jpg

[Larry Edgerton]

Six inches is a lot of material to waste. I make my forms a few inches longer than the length of the finished product but the working pieces are only slightly longer than needed -- maybe 1/2" to 1". For instance, on my compass table (below), the apron was formed in four pieces, each being a lamination of nine layers. The total length of a segment was determined by the length of the outside of the curve. I added an inch to that length and cut all pieces accordingly. Using plastic resin glue and my vacuum press meant I had no springback along the curve.

http://bbarnold.com/images/tbl_cmps1_a.jpg

I work on large architectural peices.

[Gary Muto]

That is a Great idea. I never would've thought of it, but it makes perfect sense, and so simple. This thread has me motivated to tackle that curved front table that I've had in mind.

[Jim Finn]

I have done wet laminating using oak to make this sleigh. Soaked it overnight and glued up and clamped to shape while still wet using titebond 2. Let it dry in form for 3 days. Worked well for me.

[David DeCristoforo]

Hear's "the thing". If you are only using a few layers and/or you are making a very tight radius, "pre-bending" makes sense. But if you are laminating to begin with and there is no particular reason to limit the number of layers, soaking and pre-bending is not necessary. The thicker your layers are, the more force will be needed to get the bend tight and the more likely you are to get "springback". So it would be logical to use more, thinner layers which can be formed to your curve with minimal force.

Also, remember that vacuum pressing will not provide nearly as much "localized" force as you can achieve with clamps and "matching" forms. So if you want to vacuum press your curves, you need to make sure that you can easily bend the curve "by hand". Vacuum pressure is limited to an absolute theoretical maximum of 14.7 PSI. This can add up to a tremendous amount of pressure over a large area. But with smaller pieces and stiff laminations, vacuum pressing may not be the best option.

[Tom Lindsay]

A note to Brian... I did subtract the expected thickness from the "male side" of the form (a few other posts I read about building lamination forms warned me about that).