I will be gluing two pieces of bendy plywood in dados for a chair bottom. These have a tight tadius and have to be worked into both sides, along with five cross pieces in mortise and tenon joints. Dry runs have shown it will take at least fifteen minutes.
Can anyone recommend an epoxy for this? I am a little afraid to try this with titebond for lack of open time.
Thanks
Edited 6/13/2008 9:09 pm ET by cmiltier
Replies
There are plenty of epoxies that would work for this except the 5 minute stuff, and or if the temperature is too high. If you want extra long time, you can get a slow kick, but you shouldn't need that unless your shop is up around 100º.
However, when it is warm, you don't want to mix it and leave it in a mixing container with much depth for long. The catalytic heat will cause it to go off quicker than if it is in a shallow tray, where the heat will dissipate.
This is not a problem if you have everything laid out, and just go to spreading epoxy, then get to the assembly after all of the joints are buttered, which could give you an hour or more.
Most epoxy needs, or benefits from thickening when using it for a joinery adhesive. I use colloidial silica, and mix in enough to have a viscosity between latex paint, or mayo for most work, but to bridge a big gap, I may make as thick as peanut butter.
You can google West System, or System 3, which are the most common or who advertise the most, but the one I use http://www.fgci.com/. The 1 / 1 mix is a little thicker than most already, and very forgiving on the mix ratio, and the price is a lot lower than the others.
If you are new to using epoxy, you should ask for their technical manual. I have done assemblies that took hours to assemble all of the parts. There is just no other way they could have been done otherwise.
The epoxy I use has 5 min open time and I only use when bonding non-wood stuff. I like plenty of open time for everything I do and am willing to sacrifice extra clamping time. Currently I use Titebond Extend for everything. At least 10 min open and am sure I've pushed it to 15. Of course it depends on how thin you spread it and exactly how you count 'open' time. After 5-10 min it loses it's slipperyness (as in sliding a tenon home in a slik manner) but with good clamping preassure I think would bond great. I think that Titebond Original would be also relatively good in these respects. My goal is to reduce the stress of glue-ups. No matter what it will always be a little exciting, like pouring concrete, but more open time and good music helps.
Brian
I think epoxy is an excellent way to go for this sort of project.
I've had excellent success with epoxy from Raka. Their 606 hardener is very slow--pot life of 25 minutes at 77°F for a 3oz. mix. Longer in cooler conditions.
As Keith said, you don't want to mix too much at one time due to the heat generated.
If you need any gap filling you can add fillers such as the colloidal silica that he mentioned. You can also use wood flour (dust from your RO sander) or even white flour.
Epoxy won't stick to most plastics. You can use clear packing tape to mask areas you don't want to the epoxy to stick to. The cured excess stuff will pop out of the plastic mixing container so you can reuse it.
I use MAS F.L.A.G. epoxy (http://www.masepoxies.com). They have slow, medium and fast hardeners. The only problem is that startup cost is high because you not only need to buy the resin and hardener, but pumps as well. In my opinion, it's worth the initial investment. I use epoxy for a lot of stuff even when I don't need the strength. The cure rate is very predictable and because the cured product is clear/amber, the glue lines hide well under a finish.
Another choice for your situation would be urea formaldehyde glues, as they have long open times. Some are put off by the chance of off-gassing, so this glue is not for everyone.
If you use epoxy, be sure to spread into very thin layer immediately after mixing. Could pour into cookie tray or similar.
I don't think epoxy is the best glue for the job. It is very expensive and, unless the bending will be subjected to outdoor use, is not the best glue for the job... but it will work. Instead, look at using a "Urea Formaldehyde" glue, also called Plastic Resin glue. It is much cheaper and is the primary glue for bent laminations. http://www.woodcraft.com/family.aspx?FamilyID=5350
See the FWW 6 essential glues - http://www.taunton.com/finewoodworking/Materials/MaterialsPDF.aspx?id=24128
If you go with epoxy, I love West System epoxy. I use it all the time.
Thanks for the replys.
I got some systemthree epoxy with the #2 hardener. It is supposed to give me twenty to thirty minutes of work time. I ran out of time this weekend so I will give it a try next weekend.
Even though the instructions say it will give you 20 - 30 minutes, follow the advice offered earlier to spread it out in a pan or the like; especially if you need to mix a lot. In a large quantity, it will begin to cure, generate some heat; the heat accelerates the reaction which generates even more heat which accelerates the cure even more, generating more heat,,, well, you get the picture. I've actually seen the stuff boil and read stories of it catching fire. I don't want to scare you, but once it starts to "kick" you'll have noting but a container of useless goo.
I have used tubes of "extended time" epoxy from Lowes, Home Depot, Ace Hardware, etc.
I have also used the West System.
If you have a relatively small, and relatively infrequent need for the properties of expoxy, a few blister packs form the local box store is probably the most cost effective.
The West System is the most flexible, in that you can do your own thickening, filling, etc., but the up front cost can be daunting. $60 for the smallest kits, which come in two cure ranges.
The thought of using the two part resorcinol, or the water mixable phenol-formaldehyde is another route. These have quite long open times. In the projects where I chose epoxy, I needed long open time, and gap filling capability. And I have to echo the spread out the epoxy after mixing. My first time with the West System, mixed in a cup, with silica, resulted in so much heat, it got scary. And the stuff was rock hard immediatley.
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