Laminating & bending mahogany to a curve- what glue??

[preserved_killick]

I'm replacing the taffrail on my Alberg30 and have a mold built that replicates the crown of the deck. The plan is to glue-laminate three layers of mahogany (total thickness 2") down horizontally onto the mold. After a couple of test runs using pine and GorillaGlue, the shape of the mold is perfect.

I had intended to use West epoxy as the glue. As the clamping pressure at the ends of the boards to conform to the mold is not insignificant, I would coat the boards first with un-thickened epoxy, let it set up some, then add thickened epoxy & clamp immediately. I've done this before with great success, although in this case I think the springback pressure is more than I've dealt with.

Now I'm thinking about using a product called T88 by system three. It's an epoxy adhesive that's super easy to use & strong, I just don't know how well it resists squeeze-out under clamping pressure. Good glue is worthless if you squeeze it all out.

I'd love to hear what experience others have is these cases. Anyone use T88 for laminating on a curve?? Ideas & suggestions welcome. Don't wish to ruin $100 worth of mahogany in one shot!



-Jeff

[Tim]

Use what you're used to. West System will work excellently: no need to look for something better.

[CharlieJ]

Agree- and the easy way to reduce both required clamping force AND spring back is to use more and thinner laminations. If you are working with 1/2 inch pieces, slice 'em in half and use 1/4 inch thickness, minus the kerf of course.

Makes it SO much easier to bend. You might need one or two extra pieces, but that's minor.

The formula for calculating spring back is Y= x/n2 where Y is the springback, N is the number of laminations and X is the curve being bent to.

The ratio of springback to the original deflection depends only on the number of laminations. The ratio does not depend on the properties or thickness of the wood or the geometry of the curved form. Thus, for two plies, the springback is one quarter of the initial deflection, or one ninth for three plies and one sixteenth for four plies.

But the thickness of the plies sure makes a difference in the pressure required to bend and clamp. Also, an odd number of lams seems to make for a better finished product- I don't know just why, but it does.

[Hirilondë]

I agree with all the above for starters. Keep in mind that the glued up piece does not have to achieve the exact curve it will be applied to. A little spring back can be rebent during installation.

Also, an odd number of lams seems to make for a better finished product- I don't know just why, but it does.

PFM. pure expletive magic

[CharlieJ]

ROFLMAO!! Gotta be that, for sure.

[preserved_killick]

Thanks Guys.

I'll stick with the West epoxy.

I'd love to use more laminates, but each layer of wood is a single piece of wood cut from a 12 inch wide board that is expensive! My taffrail has two curves, the crown of the deck, and the curve of the transom with the latter being the greater. I'm laminating for the lesser curve, and cutting for the greater hence the cut from a wide board. Picture a drawn-out rainbow shape for each layer. Since I can't resaw a 12'' wide board, I can't buy thicker stock for this..I'm buying 3/4 and planing down. Total thickness is 1 7/8". What's worse, is that the place I buy my wood won't cut lumber that leaves shorts, so I'd need to buy another $80 board to get another layer (I'd get two layers from this).

At this point, we have the mold perfect for three layers of wood, as tested with pine and Gorilla Glue. Funny thing that formula. Since I had the old taffrail to use as a basis to begin my drawings, I used that formula to calculate spring back and was so confident I nearly went straight for the mahogany. Good thing, since I was off by nearly 1/4 inch!

I hope the epoxy resists squeeze out as much as the gorilla glue does. I'll take some pictures here soon.

-Jeff