Glue for torsion boxes

[Jim O'Dell]

Hi all! I just did a search on torsion boxes. Is the general concensius still to use the Tightbond II glue? I will probably be using 1/2" plywood for the inside, and exterior grade 3/8" plywood for the skins unless anyone has an idea of something better to use. TIA!!!. JIM.

[Keith Christopher]

I used Titebond for mine. Seems to work ok, no complaints.

[Jim O'Dell]

Thanks Keith. I need new glue, so I'll get a quart of the Titebond II and give that a shot. Jim.

[Doug Shepard]

Jim. You didn't say how big your torsion box is. Is it big enough that glue setup could become an issue before you can get it spread on all the inside cross-pieces and the underside of the skins? If so, you might want to get the Titebond II Extend for a slightly longer open time.

[Jim O'Dell]

You're right, Doug...it could make a difference. There will be 2 of these, roughly 88" tall X 60" wide. Using for outswing doors for the shop to replace a 10' wide roll up door that is there now. I'm thinking that after dry fitting, that I'll take it apart, glue, assemble and put a brad in each joint just to hold it while it dries (I've wanted to say that for SOOOOO LONG!!!), then put glue on the top webbing and drop the skin on top, nail that in place, flip, insulate with rigid foam board and repeat on the other side. Do you think the regular Titebond II would set up too fast? If so, I will take your advice and get the Extend version. THANKS!! Jim.

EDIT: I also thought about using liquid nails. Any thoughts on which would be better?

[Doug Shepard]

... Do you think the regular Titebond II would set up too fast? ....

EDIT: I also thought about using liquid nails. Any thoughts on which would be better?

I had a hunch with 3/8 thick skins that your boxes might be pretty big. As far as the Titebond II setting up too quick - maybe. I think it all depends on how many crosspieces you have to get glue on, whether you can get a helper or not, and how neat you try to be when doing it. Were you also going to lay glue beads down on the skin underside where it'll lay on the cross-pieces? Or just putting a heavier bead down on the crosspieces? Doing both might be at the outside limit of TB II time and maybe even the Extend. I doubt there's much reason to be worried about excess glue runs inside the box. If you hurried and used a small cheapo paint roller to get glue on everything, you'd probably have enough time. For the most part I just always go with the Extend glue so I can take a bit more time. I think the bottle says you get another 5-10 mins open time vs the TB II, and the only other difference is that the Extend has about a 5 degree higher min. application temp. The only problem is that it's not as widely available at local stores. HD doesn't carry it. Not sure about Lowes. If you've got a Rockler or Woodcraft close by, I think they both carry it. I usually get mine mail-order.

I had the same thought about construction adhesive after I posted. I don't use it often enough to remember, but I think that's more of a 24-hour cure? Or at least some versions of it. That might not be a bad way to go either and would let you take more time to do a neater job.

[Steve Wargo]

For doors that big, I think that Titebond will certainly set up too quickly. Even if you brad the pieces. I'd go plastic resin. Unibon 800 works great and you can control the set time with the mix.

[John Miliunas]

FWIW, TB III also has a longer open time than the II and is, by some recent testing, one of the strogest. I've been using III for about 1/2 year now and am pleased with it. I haven't done that many real big projects, but I'm just naturally slow, so the longer open time helps.:o :) :cool:

[Alan Turner]

With the Unibond 800, it dries quite rigid, does not creep, and is for all practical purposes waterproof, which might be an issue for you. Mix it and apply with a foam roller. It will dry without air as it is a 2 part adhesive. I think the price is $17 for a 1/2 gallon package, and if you keep the resin in the fridg., it will last 2-3 years. This is a big project, and it would be a shame to have to do it twice.

[Joseph N. Myers]

Another vote for TB III. Used it for over a year and love it. Besides greater open time, it is much more tacky, i.e., will stay in place better while setting up, which is great for the stuff I do. Clean-up seems to be better but maybe that is just me.

Regards, Joe

[Jim O'Dell]

Thanks guys!! Lots of good info. Now to decide which way to go!!!! Jim.

[Mark Singer]

TB III (torsion box 3):eek:

[Doug Shepard]

Looks like a lot of satisfied TBIII users here, but I just checked Franklin's site and here's the differences:
TBII - 5 mins open time
TBII Extend - 15 mins open time
TBIII - 10 mins open time

For this big glue up you might still want to go with the Extend if you're going to stay with a PVA glue.

[Jamie Buxton]

Looks like a lot of satisfied TBIII users here, but I just checked Franklin's site and here's the differences:
TBII - 5 mins open time
TBII Extend - 15 mins open time
TBIII - 10 mins open time

For this big glue up you might still want to go with the Extend if you're going to stay with a PVA glue.

Can somebody explain to me what "open time" means in the context of gluing wood together? We're not concerned with how long the glue takes to cure while standing open. We want to know what's happening in a well-machined joint.

[Keith Christopher]

get a good glue roller from joewoodworker or one of those bottles they see from woodcraft with the built in roller. makes gluing up large things like the baffles in a torsion box easy.


Keith

[Doug Shepard]

Can somebody explain to me what "open time" means in the context of gluing wood together? We're not concerned with how long the glue takes to cure while standing open. We want to know what's happening in a well-machined joint.

It's how much time you've got to get your pieces assembled after applying glue to them before the glue starts setting up. Any longer than that, a couple of things start to happen. For nice snug fitting joints like M&T's or dovetails, you sometimes cant even get them to slide together once the glue stiffens up. Or if you can get the joints to go together, you don't end up a good glue bond as it's no longer liquid enough to meld into a single bond. You essentially get a hard film on each of the mating surfaces that doesn't really fuse together well.

[Jamie Buxton]

It's how much time you've got to get your pieces assembled after applying glue to them before the glue starts setting up. Any longer than that, a couple of things start to happen. For nice snug fitting joints like M&T's or dovetails, you sometimes cant even get them to slide together once the glue stiffens up. Or if you can get the joints to go together, you don't end up a good glue bond as it's no longer liquid enough to meld into a single bond. You essentially get a hard film on each of the mating surfaces that doesn't really fuse together well.

Hmm.. Is there some standard film thickness to measure this? Consider two situations. In the first, I spill a puddle of some PVA glue on the concrete floor. It may be a good eighth of an inch thick. In the other, I spread a thin film of the same glue on a piece of wood. I squish it around with my thumb. It will set up enough to grab my thumb in a few seconds. In contrast, the puddle will be liquid for tens of minutes (particularly if I step in it and then go into the house :( ).

[Doug Shepard]

Hmm.. Is there some standard film thickness to measure this? Consider two situations. In the first, I spill a puddle of some PVA glue on the concrete floor. It may be a good eighth of an inch thick. In the other, I spread a thin film of the same glue on a piece of wood. I squish it around with my thumb. It will set up enough to grab my thumb in a few seconds. In contrast, the puddle will be liquid for tens of minutes (particularly if I step in it and then go into the house :( ).

Good question. I'm not a chemist or a glue expert - just somebody that's been bitten too many times pushing the open time envelope by trying to glue up too much at once. But I suspect exposure to air has a lot to do with it. I'm willing to bet the puddle probably has started to skin over, but the glue underneath the skin is able to stay liquid longer since it's now got an air barrier. The thin film on wood is almost all surface area exposed to the air.
If air doesn't play any part, then I guess I don't understand how it can stay liquid in the bottle, but as soon as I forget and leave the cap off, the next time I go to use it there's a solid block of hardened glue in the bottle or a thick plug on top with just a little liquid left at the bottom.

[Chris Padilla]

Well, if you cut the cross pieces to very tight tolerances, I doubt you'll need to worry about glue them.

I made torsion boxes out of 3/4" MDF and I set up my dado to cut notches that were so tight, that upon a test fit, I gave up trying to get the test pieces apart so I didn't worry about gluing them. Plywood varies more in thickness than MDF but MDFs "dead on" at 3/4" (or 1/2" or 3/8" or whatever) makes it great for torsion boxes IMO. It is also cheaper than plywood.

With a nice foam roller, spreading some hot poly glue (Gorilla if you like, nice long open time compared to PVAs), you should be fine. I was....

[Randy Meijer]

Sorry.......torsion box is not in the vocabulary of a simple pen turner like myself??? Can someone help me out??

[Jim O'Dell]

Randy, a torsion box is basically a hollow core door. Solid outside edges, thin "skin" on the outside, and a grid of some sort on the inside. Hollow core doors use a cardboard like substance. In fact, you can think of cardboard as a torsion box. The design gives the strength and weight savings. Does this help create a mental picture? Jim.

[Randy Meijer]

Got it, neighbor!! Thanks.

[Steve Aiken]

I wonder if there's any advantage of gluing up the joints in the 'web' pieces of the torsion box? The strength of the torsion box comes from the surface tension of the 'top' and 'bottom' skins, so I'm thinking probably not any value in gluing these joints. Probably is good to cut the parts of the 'web' so they fit tightly though.

Steve

[Jim O'Dell]

My thanks to all for your insights. I will probably wait until I get everything cut to decide which glue. Do a walk through, and see how much time it takes. I may even use different glues for different portions of the build.
I appreciate your time and knowledge! Jim.