I am building a kitchen corner-cabinet which will have a 36″ radius granite top. The base is faceted i.e. a series of flat surfaces around the front so no one spot ends up recessed too far behind the top. The bank of drawers down the center of the front are angled out from the sides to come to a slight point in the center. Because the front corner joints are not square, I decided to use all box or finger joints for all four corners and the center joint in front. The drawer sides are all 1/2″ baltic birch & I used West epoxy to give me plenty of open time & I hoped lots of strength. The fingers are all 1/4″. All went well with assembly but now I find the joints are very fragile & the glue bond breaks free but no wood damage.
It appears that the epoxy may have been absorbed into the wood & not left enough to form a good bond between surfaces. Should I assume all surfaces are now primed & redo the glue job with more epoxy or could I leave the drawers intact, jar them just enough to break the bond & reglue them with cyanoacrylate(sp?) (crazy glue)? This is a contract job.
I have all kinds of speculation; hopefully someone who has experienced this sort of problem can give me an idea that will work
Paul
Replies
Paul,
I've glued up over a thousand finger (or box) jointed drawer boxes - some very big and complicated, and I've always used Titebond II glue. You do have to work fast, but I've never had a problem with strength or glue absorption. Although I'm a proponent of epoxy, I think it's overkill for drawer boxes, and it must be a pain to clean up. I use a small brush to apply the glue and work fast.
Baltic birch is great stuff for lots of applications. However, maybe finger joints isn't its best use. Basically, wood glues only on facegrain to facegrain contacts. If you consider one glue face in your finger joint, half of one side is end grain, and half of the other side is also end grain. When you glue them together, you really only have 25% of the bonding face that you'd have if you used solid lumber.
Over 90% of the drawer boxes I've assembled are of 11-ply Russian birch, all without a failure. Its stable, strong, and makes for very good finger joints.
You mixed the epoxy too hot. Could have been ambient air temperature or it could be that your just had too much catalyst. You could try super glue but I sure as heck wouldn't tell the customer. And, I'd almost be willing to bet that you would be back in six months or less.
The sad part is that they are finger joints. I would assume that you built them proud and sanded them. If so, they are now unique so if you try to clean them with a scraper or chisel, its never going to fit right again. You certainly cant use any type of solvent that I know of. I think if you found something it would still require some type of scraping. I'm sorry but I just cant see any way to fix it now. You might be able to save yourself half the work by changing half of the pieces to 3/8 joints then remaking the remaining half at 3/8. I cant see the pieces so I dont know if that would work or not.
The box joint is just one step below the Dovetail in strength. You only need white carpenters glue to make a good solid joint. If working time is your problem then either wipe or dip the jointed surfaces in water before you apply the glue to extend the set time.
Dang, I wish I had a better response to this. I know you've done a lot of work. I just cant think of any other way to fix it. Maybe there's a miracle worker out there that can help. Don't take my response as the only possibility, wait and see what this thread turns up.
Steve - in Northern California
Another possibility is that the glue lines were just too thin. If I remember correctly, the West System instructions specify not clamping too tightly because it is possible to starve an epoxy glue joint. That would also apply to the surfaces that slide past each other when you assemble the joint, if too much glue gets scraped off before the joint bottoms out.
Hi Paul,
I have used epoxy by the gallon in boatbuilding. When I use it as a glue (as opposed to a surface coating, typically with fiberglass cloth), I always add a thickener to minimize absorption in the wood. Otherwise you get glue-starved joints that won't hold. This is what happened in your box joints. As someone else pointed out, most of your gluing surface in plywood finger joints is end grain, and that makes the glue starvation problem even worse. Even with a thickener (silica, micro balloons or wood flour), I normally apply the thickened epoxy and let it soak in, then apply more of it before putting the joint together.
As for re-gluing with more epoxy, it may work, but the glue bond won't be very strong. When I re-coat an epoxied surface, it needs to be done within about 12 hours of the previous coat, so that the next coat will form a chemical bond with the previous coat. Otherwise the previous coat will have to be sanded, in which case all you can hope for is a mechanical bond, which is not as strong. Then there's this thing called amine blush. It's a waxy film that floats to the surface after epoxy cures, and subsequent applications of epoxy won't stick to it.
I know none of this sounds good, but the up side is that finger joints are inherently very strong and you don't need perfectly strong glue joints to make it stay together. I would take some epoxy-coated scrap and see how well the CA holds it together. Since the wood is already primed, the thinner CA as opposed to epoxy may just be your best option. If that looks promising, I would add reinforcement by doweling the finger joint together with a 1/8" hardwood dowel (by this I mean drilling through all the fingers after the joint is glued together). The hole could be drilled from the bottom and stopped short of the top if you don't want it to be noticed.
Rick
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