Bent Laminations

[alexy]

I am getting ready to do a bent lamination, and have questions about adhesives and springback.

I have heard that urea formaldehyde or plastic resin glue is the best to use for this application because of the long open time and lack of creep once set. I am having a hard time finding it, though. I can get a gallon from Highland Woodworking but because of its relatively short shelf life, I would end up throwing away 95% of it. Anyone know a good source for small quantities (Atlanta area desired, but online source okay, too) or whether another type of glue would work as well. My application is not load-bearing, and in fact will be "captured" by another structure. I'm laminating 4 pieces of 1/8" thick poplar for edge banding of the inside of an elliptical arch cut in plywood.

I have a form for bending my lamination, that I made slightly undersize, anticipating that there will be some "springback" when the lamination is removed from the form. Anyone have any ideas or formulas for estimating how much that will be in advance, or is it just a case of trial and error?

[Lew Hodgett]

alexy wrote: > I am getting ready to do a bent lamination, and have questions about > adhesives and springback. >

I use epoxy with a slow hardener.

West System, while expensive, is readily available in small quantities.

Check for an outlet in your area using the West site.

Take a look at Fred Bingham's book for spring back info.

Have fun.

Lew

[J. Clarke]

I think the stuff you're looking for is Weldwood Plastic Resin Glue, which is a urea-formaldehyde water-activated dry powder FAA approved for aircraft construction (in other words this is seriously good stuff). You can get it online in one pound containers for about 8 bucks a pound and shipping. Two reliable sources are Aircraft Spruce and Specialty and Jamestown Distributors .

It used to come in pint cans but now the smallest seems to be a pound. I don't know what the real shelf life is--officially it's "1 year minimum" and I wouldn't use it older than that for an aircraft, but for noncritical uses I have a can that I've been using up gradually that is at least 15 years old and still seems to set up fine.

Ace Hardware lists it online, but only in 4.5 pound containers for over 20 bucks--you might want to call around and see if they have the one pound size in the stores.

Read the instructions carefully--the stuff is reasonably forgiving but it is possible to screw it up. That part about "cannot be successfully removed from most surfaces once set", they _mean_ it--don't wear clothes you care about. The only way to get it off wood once it cures is to scrape or sand. Also, when the squeeze-out sets up it's _hard_. Doesn't stick to metal though, at least none that I've dripped it on. Nice thing is that if you get to it before it sets you can clean up with water.

I haven't used it so can't say how good it is, but try which is an Excel spreadsheet that purports to calculate springback for laminations.

If you google "lamination springback calculator" you'll find some others.

[MikeG]

Dap makes a powdered version of urea formaldehyde or plastic resin glue . You mix up the quantity needed for the task at hand. here is one example...

found some at my local Ace store.

MikeG

[Teamcasa]

Alex, For the project you describe above, I would use polyurethane glue. Its has sufficient open time for your project. I only use plastic resin glue when I need + 20 minutes to get the project clamped up.

Dave

[alexy]

I've thought about that, but how is it for creep? My impression is that UF and epoxy are better in this regard. But maybe that's academic in my relatively low-stress project?

[Teamcasa]

snip

I use blue tape to stop creep. Its really not much of an issue unless the bend is severe. Just make sure you wear nitrile (blue) gloves. Dave

[Lew Hodgett]

SFWIW, For the price of Gorilla Glue or equal, you can add maybe 10% and get epoxy.

There is no comparison between epoxy and Gorilla Glue.

Lew

[alexy]

I found it at the 5th Ace I called. Suspicious of the shelf life already used on the store's shelves, given the dust on the container, but decided to go ahead based on your experience and the advice quoted above. (and my boldness was helped by the whopping total of $6 at risk)

Lots of neat stuff in that spreadsheet. Thanks.

[alexy]

Thanks, Lew. I wonder what the trade-offs are between UF and epoxy? Sounds like you are a "fan" of epoxy, but there are always tradeoffs.

[alexy]

Either I am misusing the term "creep", or I don't understand what you are doing with the blue tape to stop it. I thought that creep in a glue joint referred to movement in response to sheer forces.

[Teamcasa]

Lew LOVES epoxy (and must have stock WestSystems). He suggests it for virtually every fix where an adhesive is used. Since he works on boats, its a natural choice. For the rest of us, we get to use several diffrent glues.

Dave

[Teamcasa]

You are not. Creep is what happens to the wood sandwich as clamping pressures are applied. Blue tape will hold it most of the time for flat stock glue ups, it has a hard time when the form includes a bend and twist. Unless your bending form incorporates a twist as well as a bend, you should not have a problem with creep. If you do, and blue tape will not hold, (try it without glue first) apply clamps and cauls to prevent severe creep. Use clear packing tape on the cauls to prevent the adhesive from sticking to it.

Dave

[Lew Hodgett]

Actually, I don't use any West Systems.

They are not competitive for my applications.

The reason I suggest them is that they offer small quantities, are readily available almost every place, and they offer very good tech service.

Lew

[Teamcasa]

What do you use? Dave

[Lew Hodgett]

I work with Diversified Materials in San Diego.

They use several different suppliers based on price and availability.

Laminating epoxy is strictly a commodity, IMHO.

Lew

[George E. Cawthon]

.

I concur on the shelf life, my can of Weldwood Plastic Resin Glue is over 30 years old. The lid is tight, has never frozen but the high temp has been around 90 degrees in the summer (stored in the garage). I think the last time I used it was about 5 years ago and it worked fine. You need close fitting joints as it doesn't fill.

Lots of glues indicate a short shelf life, but with reasonable storage and use, the shelf life can be pretty long. My can of Weldwood Waterproof glue (a liquid resorcinol resin plus a powdered catalyst) is also 30 years old, actually I bought it sometime in 1972, and my last use was 2 years ago on a ceramic figure that had an ear knocked off. The ear is still on after 2 years outside being sprinkled in the summer and the sitting in the hot sun and freezing and being snowed on in the winter. Good stuff.

((Snipped))

[alexy]

Okay. That's not my understanding of the term. I think it refers to a property of the cured glue line. From an engineering dictionary: :Creep :the dimensional change with time of a material under load.

and from the Franklin Global web site: :What is creep in an adhesive bond? :Creep or cold-flow in an adhesive bond is the deformation of :the bond line under a stress or load over a period of time

[alexy]

And his love of epoxy may be well founded--in its many formulations it is wonderfully flexible. But I still believe that there are tradeoffs in selection of any construction material or technique, and I'd like to see some discussion to form the basis of an informed choice.

[J. Clarke]

Cagle, in "Handbook of Adhesive Bonding", a well known engineering reference, recommends UF or RF over epoxy for wood-to-wood joints exposed to weather. I don't remember why now and my copy is not readily accessible. However he was writing over 30 years ago and the available epoxy formulations may have improved since then.

Personally I generally use Titebond or PU for the convenience, but if it's mission-critical indoor and I've got a good fit I go for the UF and mission-critical outdoor the RF.

OTOH, I've got an assembly I'm going to glue up with T88 epoxy tomorrow, the reason being that it's outdoors, the temperature right now is going down into the high 30s at night, and T88 will cure at that temperature (eventually) while UF and RF aren't rated to cure below 70 and the rest not below 50.