Cypress Bent Lamination Questions

[nelsone]

I have been asked to make a hammock stand and am thinking of trying to do some bent lamination. I want to use cypress. The questions I have are how thick would you make the laminations and would TB3 be satisfactory for gluing the laminations. Here's a pic of the basic design I want to use.

 

[NCPete]

Ed, I am not sure if the open time of TB3 is long enough to stick together a laminated project like that... too bad, because the water resistance properties would certainly be desirable.

 

[nelsone]

I have never used a urea resin, but saw where a custom stair builder used it for their rails. Does urea resin hold up in outdoor conditions?

 

[NCPete]

not sure here! interested in the answer.

 

[mkepke]

Ed - I've never used cypress, but I'd guess you might get away with up to 1/4" material as the curves don't look very tight. That said, thinner is better - everything is a battle with thick stock !

Plastic resin glue would be ideal.

-Mark

 

[nelsone]

Thanks Mark! When the plastic resin glue is mixed, do you just use a brush to apply it?

 

[SkintKnuckle]

Ed, Assuming that you're going to put your piece outside in the weather, you'll need an adhesive that will pass a Type I test. Breifly the specifics of that test are that a 1x1 piece will pass a 3 cycle water boil/dry test without significant delamination. The key there being significant, a small amount of shallow delamination at the joint is allowed. Here's your options:

1- Titebond III - rated to pass type I, probably doesn't in all cases and applications (Franklin's results would have been carried out under perfect lab conditions). Not terribly expensive, safe to use, glueline is almost invisible, easy to find.

2- PRF or RF resin - passes type I EASILY, is expensive, difficult to find, has relatively hazardous chemicals (although I wouldn't be afraid to handle myself). Requires good clamp pressure and tight fitting joints. Needs at least 70 degree temp during cure, which is at least overnight. Also gives BLACK gluelines, which will be noticilbe in your cypress, they'll look like the glue joints in exterior grade plywood.

3- PUR (Polyurethane, or Gorrilla Glue) - passes type I easily, moderately expensive, relatively hazardouls chemical (again I would use it in my basement shop). Fairly easy to find. Requires good clamp pressure and tight fitting joints, I cannot stress this enough. PUR's do not act as gap fillers! Will give you a nice glueline that will look nice with your cypress. If I were building what you're taking about, this is the way I would go. You'll want to spritz the wood surfaces with a small amount of watern first, here's how I use it at home. Get an old windex type sprayer, spritz both wood surfaces, spread the adhesive, and clamp over night. There is a foaming action as the adhesive cures, it is there to drive the adhesive into the wood pores, the action is very stong, hence the need for an unusual number of clamps. If you don't have access to as many clamps as Norm Abrams has, don't even this about this, a few clamps is NOT going to get the job done.

4- You could also consider epoxy, but if you go this way, get out your checkbook.


Regarding your question on UF resin, In a cold press application, like you have at home, the best your should be able to get is a type II bond. This is a less strigent test than the type I above. It's for indoor applications or very limited outdoor exposures only.

Hope this helps, PM me if you need more details.

 

[NCPete]

Thanks Martin!

 

[Makinsawdust]

Martin,
Since you sound like you maybe in the glue industry, I've got a question. Do you know anything about the elasticity properties of these glues? I've heard the yellow glues have quite a bit of spring back compared to say UR and PR. Is that true? Is there a table somewhere with data so that one could calculate the amount of over bend needed to get the desired end results?
Rob

 

[nelsone]

Thanks for the info Martin. Lot's to consider. I have used PUR glue before and was less than happy with the process, very messy!

 

[dino drosas]

I would go with the plastic resin glue. Comes in powder form and mixes with water. You can add a lightening powder to get it the same color as the wood. Plenty of open time. It can be applied with a roller or squeegee, and there is no creep after it dries. A greater number of glued laminations will give you more strength.

 

[SkintKnuckle]

Robert, PVA's do give a more flexible glue line than the thermosetting types like UF, PRF, PUR. I'm not sure you can calculate the amount of springback you'll get from using PVA in that application, since there would be a lot of other factors which would influence it, such as veneer thickness, wood species, number of plys, etc. Generally in most industrial curved plywood or beam applications the thermosetting resins are used. Either for cost (in UF resin) or for perfomance (as in the case of PRF for structural applications). By the way, a flexible glueline is desirable in many cases, so it's not all bad, it's one of the properties that make PVA a good wood adhesive. In a home curved plywood appliction, open time is apt to be a problem, so if you're going to try this, be sure to work as fast as possible to prevent dry-out. Also, and I know I'm going to be challenged on this, yellow glue is just white glue with a bit of dye added. That began with the Elmer's Woodworking Glue some several years ago, and many other manufacturers jumped on the bandwagon, perception is 90% of performance. The major differences between PVAs are the type of polymer, fillers, and glue solids in the particular formulation.

Ed, the PUR's I've used didn't have much more squeeze out than most PVA's. Perhaps you're trying to apply too much. All you need is about 3 mils, hence the need for the clamp pressure. In any case you're going to need to trim the edges of your curved wood. You can spread them or any of the adhesives mentioned with a brush trimmed to about 1/4 inch bristle length, use the cheapest brush you can find, in say the 2 or 3 inch range.

Regarding the one post on "Plastic Resin Glue", be careful, that's a very general term. There are going to be at least 2 types, a spray dried UF resin formulation (which is described in the post) and the PRF where you have a dark colored resin with a smaller catalyst component added.

 

[junquecol]

In this application, I would use white oak. It is much stronger than cypress. Bends well, and is also rot resistant. Realize that when you have 200# of downward force, you have several times that inward force. I helped a friend do a repair on a bent hammock stand this past weekend. It was made form white oak. Lasted several years out on an exposed deck at the beach. I would go to a leisure products store and size up a commercial one before committing to the job. Just to be safe on sizes of the members. CYA!

 

[JackLeg]

Mike Davis should be able to offer you some assistance. That sled he made was awesome!

 

[nelsone]

Thanks for all the feedback guys! I'll let you know if I go for it! Gotta figure the forms and everything to decide if I can make it cost effectively. There is the opportunity to add another type of project to my arsenal!