Bent wood lamination glue question

Re: Bent wood lamination glue question

Paul in NJ

Hi Barry,

I have had the best luck with West System Epoxy. I also have had good luck with casein glue, the powder stuff you mix with water. These two are more rigid than your standard yellow pva.

The casein has a 1 year shelf life. I like the West epoxy, it lasts for years. The hardener might turn reddish after a few years but retains all its properties and works fine. Since I use mostly cherry and walnut, the red color doesn't bother me. I have used my 20 year old glue recently with excellent results. It is a most versatile glue.

regards,

Paul Dzioba

Re: Bent wood lamination glue question

Keith L Newton

Barry, I would use epoxy thickened to about latex paint viscosity in a vacuum bag. You don't mention what the long and short radii will be, so I can't speculate on any pitfalls there. However, for long narrow laminations like this, sometimes the bag becomes a problem, so here is a tip.

You can buy rolls for vacuum sealing food that can be cut to whatever length one needs for that process. These bags already have a texture on one side allowing the air to move rather than seal against the other side as the vacuum advances. I would roll the glued up bundle in a thin plastic painters drop cloth to protect the bag for another time. You can seal the ends with rope-caulk which is a thick caulk that comes rolled up in a box, or butyl, or any other kind for that matter since you can just cut off the ends after the cure.

For a short project like this, you shouldn't have any problems getting it into the bag, but for really long projects I've used my shop vac on blow to send a rag down and out the other end with a tag line tied to it. This allows you and a helper to pull the slippery bundle down the length while the other feeds the work while also sending some air down the tube. Just make sure to prevent any sharp corners on the front end from snagging the bag and puncturing it.

On a really long bag, I would still put a length of some kind of cheap cordage down the length alongside for easier airflow from the far end to the hose. You can tell when you've got a good seal by feeling of the wrinkles in the bag. If there are any leaks the wrinkles will be looser nearby.

Re: Bent wood lamination glue question

Jesse Cloud

I've done many dozens of lams like that. Always used plain old titebond. Never had a problem. Epoxy is hyper messy, very particular about mixing and error-prone (for me at least). If you are making this as a section of a larger piece, you may not want high rigidity - better to let the lam move with other wood.

A few suggestions:

1. Make the lams a bit (1/2 to 1 inch) wider than the final width. Glue will squeeze out and the lams may shift a bit while clamping. When the glue up is cured, take it to the band saw and rip a straight line cutting off one wonky edge.

Take that edge to the jointer and make it flat and 90 degrees to the width. If the radius isn't too small, you can cut off the other wonky edge with the table saw, otherwise, repeat the bandsaw and jointer process.

2. Do a dry clamp!! I've never bent white oak before so I can't say how flexible it is. The dry clamp will let you know how easily you can bend 1/8th lams to your form. It will also give you a sense of how long it takes to clamp up.

3. Apply glue evenly and quickly. One of those small paint rollers will do that well.

4. When you make your lams run a sacrificial board through the planer. Put a stop on the end of the board. Use that as a bearer board for the lam. That will compensate for any angle on your planer knives. A small angle that's not a problem for one piece becomes a big problem for a stack of pieces.

Good luck and post some pics!

Second the suggestions....

John in NM

Good advice there.

For adhesives, I've done this with West System (curved Morris chair arms) in a vacuum bag, Weldwood plastic resin glue both clamping around a form and in a vacuum bag, and with Tightbond 3 clamping around a form.

I found the epoxy easiest to mix but generally messiest to use.

Plastic resin glue is harder to mix - it fools you into thinking it will be too stiff as you mix it, then loosens up a little later and is just right. First time I used it I had too much water in it and it was very weak - 100% operator error. Subsequent times I used it I got it right and really like the stuff. Lasts forever out here in the dry desert, probably has a shelf life on the coasts.

Tightbond is useful if you don't mind a little springback. As Jesse points out too, sometimes you want some flex.

Re: Bent wood lamination glue question

Bruce, a MN Galoot

Titebond will work fine, since that’s not a particularly sharp bend. White oak bends pretty well. Other than that, do what Jesse recommends.

Re: Bent wood lamination glue question

Bill Tindall, E.Tn.

I have only done a few. Having done a few all of your advice was accurate for my application, including the glue.

I doubt 1/8" oak will bend in more than a shallow arc. Agree to test.

Re: Bent wood lamination glue question

Ellis Walentine

Plastic resin is my go-to for this type of lamination, but West System epoxy will no doubt work, too.

The most critical thing you need to know before you start gluing this thing up is whether the whole stack of laminates will bend comfortably to the contour of your elliptical section. Is it a gentle section of the 48" long dimension or a tight bend around the end of the ellipse. Either way, you should be able to bend the stack by hand, without clamps. If you can't do it, you'll need to thin your laminates accordingly until you have a thickness that allows this curvature without heavy clamping pressure. This will also help eliminate springback, which is to be expected in any lamination like this.

Ellis

Re: Bent wood lamination glue question

Jim O'Connor

I think given the curve you mentioned you will need to really select the wood that you cut the laminations from. Any grain runout will be a weak spot in a dry bend. I have made free standing dressing mirrors with a mirror about 4' by 1.5' with legs corresponding to your curve and glued up alright with Titebond but a bad piece of wood in the middle of a glue up is a disaster.

Re: Bent wood lamination glue question

Don Stephan

Can you tolerate some springback when the dried lamination is unclamped?

Spring back?

Barry Irby

Yes I can tolerate some spring back. I have allowed about an inch. If it comes up short and does not spring back enough, I can pad the ends.

Thanks for all the suggestions and help.

Off to finish the form and cut the laminations. Will try a dry bend. I could soak the pieces or I have a steamer but wanted to skip that if possible.

Re: Spring back?

Bill Tindall, E.Tn.

I could soak the pieces

and use what for glue? You have a gigantic resaw. Saw as thin as you need to get an easy bend. There will be little spring back with 7 laminations. There is a formula to calculate it. It only depends on the number of laminations as I recall.

Pre-bending

Ellis Walentine

I have laminated curves that were much too tight for the thickness of my laminates by pre-bending them over a hot pipe.

While we're on the subject, you can flare a laminated curve by adding a solid piece between the laminates. The piece will need to be tapered (and curved, depending on the shape you're trying to create). This is very quick and easy on an oscillating drum sander.

Ellis

Unibond to prevent spring back

Raj

the unibond also allows each ply to slip a little more easily as the piece is pressed down. You need to watch your shop temperature and the open time is better with this.

Re: Spring back?

William Duffield

The formula is published in FWW #119, July/Aug 1996, page 10. Since it is copyrighted, I can't reproduce the article here, but if you provide me an email address, I'll see what I can do.

Re: Bent wood lamination glue question

William Duffield

Some additions to Jesse's suggestions:

3. Use the shortest nap roller you can find, and cut it so it is only slightly wider than your lamination. Epoxy is too expensive to waste it by throwing it out with the roller.

4. Jesse's advise is right on. Instead, you could flip every other lamination over or turn it end for end to save some time and materials, but you run the risk of getting confused in the process. That said, I've not experienced that planer blade alignment problem, but I would surely remember to do something about it if I had.

Re: Bent wood lamination glue question *LINK*

Sgian Dubh

William, I've collected a few of the formulae used for estimating springback. I put them together in a small PDF as attached here.

I have to admit that I think the usefulness of all the formulae is a bit hit and miss, but here they are anyway. Slainte.


Springback formulae for bentwood laminations.

Results...and Thanks

Barry Irby

It's funny what you learn and how obvious some mistakes are after you make them.

The way I have always made forms is to make a shape to bend the wood around the outside and use a ton of clamps. I made half an ellipse and cut 9 square holes in it 1 1/2" back from the edge. I made shackles, pieces that inserted through the form and a similar piece for the outside with Allthread rods to pull the second set in tight. The form was five layers or 1/2" MDF. The strips were 1/10" thick and 3 3/8" wide and 6' long.

Did a practice run with one strip and then all ten. Worked fine.

Slathered them with a fresh bottle of Titebond III. Quickly onto the form, fastened the center and then worked my way around.

After the 9 shackles were in place I realized I had some problems. The stack had slithered out of alignment and was fanned out a bit on each end. Tried loosening the shackles and clamping them back in to a stack. Not much luck. Also realized the edges did not pull down tight where they over hung the form on each side. Added clamps, lots of clamps. Ended up with 37 clamps on it.

What did I learn? Now I know why you should use an inner and outer form. Much more reliable assembly and faster. Keeps the stack aligned better and applies pressure all the way to the edges. My thin plies cupped because of the water in the Titebond. Should have used Epoxy. Less warping from the wetting and more open time for fiddling. Part of the 37 clamps was just clamping the edges together between the shackles.

The good news is that in spite of my poor understanding it's a success. I hand planed one edge straight and ran it through the planer and cleaned up the edges. (That was interesting, running a really crooked board on it's edge through a 12 inch planer) In stead of the 3" I was shooting for I got 2 3/4" which works out fine. Got almost no spring back. The white oak bent fine, no run out or splitting. It's going to work well.

Thanks for all the help, just wish I had listened better.

Re: Results...and Thanks

Jesse Cloud

Hey Barry,

Sorry the glue up was disappointing. My armchair guess would be too much glue and no/not enough cauls. Maybe also too wide a form. Maybe the pic below would help. The dark brown wood is the workpiece (a chair leg). The lighter wood is scrap wood cut into lams for a flexible caul (no glue between them). If you look closely you will see that there is an additional caul between the clamp head and the scrap cauls -- these are scrap hardwood pieces. There are clamps on both sides of the form. For this particular piece I used about fifty clamps.

This pic was taken on the 16th glue up for this project. There is some glue on the form, but not so much given how much it was used. When applying glue my method is to draw pencil lines on the lam and spread the glue thin enough that you can barely see the pencil lines. Main thing is to be sure there is glue on all the surface. More glue means more sliding.

Another technique for preventing sliding lams, not used here, is to make some substantial scrap pieces about twice as long as your lams + caul-lams are high and screw them onto the form at 90 degrees. This requires that your form is not much wider than the lams.

Lams want to slide. If I was having issues with that I would use a scrap piece and a rubber mallet to bang them back into position.

Lams cup when not held into position - not enough cauls/clamps.

Hope some of this helps with the next glue up. Good luck and hang in there!