Thanks for the helpful advice. I inspected the contact between the face frame and the unit with the clamps on (dry) as shown in the photos I posted. I could see a gap in one spot and made a mental note to add a clamp there as per your suggestion.
When I removed the clamps and the face frame to prepare for the actual gluing, I noticed that there was a very slight "lump" of glue near where I had seen the gap; it must have squeezed out of the end of the dado when I glued in the shelves. A few passes with a block plane evened it out nicely, there, and in another location. After I applied the glue, face frame and clamps, I inspected that area again: No gap.
At this point it really was more curiosity than worry. I'm always up for learning something more. In any case, the gluing was done yesterday evening. :)
I can't speak to your experience or process, but I glue thick, solid edge banding/reinforcement to plywood all the time and get very strong results. I routinely test small sections of the joint from where I've cut a shelf to length and end up with a cut-off piece of shelf that is
1/4" to 1" wide. It is very difficult to break this joint and it rarely fails at the glue line. I stopped using fasteners (screws or nails) for this joint, several projects ago, as they proved to be unnecessary overkill.
As to strong.... well, strong is relative, isn't it. In the case of the OP's bookcase, the shelves look to be about 18" wide in my estimation. Not only does he not need any reinforcement on those shelves, he could probably store electric motors on them with no deflection. :-)
The face frames in the OP's bookshelf are just that, face frames. Face frames in cabinetry *do* add rigidity and strength, but in modern cabinetry are much more cosmetic/esthetic. I know of designs in which the face frames of a cabinet is intended to provide critical strength to the construction. This is certainly not the case in the OP's bookcase. The OP's face frame, IMO, is purely cosmetic and could be attached with
18ga trim nails and it would be stronger than needed for the intended purpose. Gluing it on now means it would likely hold up in a circus elephant act. :-)
Moving on to a broader discussion of solid edge support.... If I get to the point where I want the edge banding on a plywood shelf to act as reinforcement against deflection, I will often cut a rabbet in the solid wood banding to add strength, like this...
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This is generally for shelves that are very wide, like 3feet and more. This adds a great deal of strength and gives the shelves a thinker front profile, which I think looks better. So, it serves a dual purpose. I would never think (any longer) to have any fasteners in this joint. But I can assure you, even without the rabbet, I would use only glue.
I addressed this in my previous post, but from the OP's pictures, that face frame could be more than adequately attached with trim nails. Those shelves are very narrow and are glued/dadoed in as integral segments of the case. IMO, they need no reinforcement at all. The frame certainly will add some strength, especially if glued. But glue AND fasteners is beyond overkill and simply a waste.
I don't know about him but I have *NEVER* had a glued joint fail. One of mine, that is.
A while back I had to make a couple of glued up arched jambs. I drew my arc on a piece of ply, put short pieces of 2x4 on edge at a few tangents. I attached them by squirting some yellow glue on them and pressing in place (no clamps). When I finished with the jig I reclaimed the plywood by knocking off the 2x4 pieces with a hammer. Generally took more than one hard blow and each one took plywood with it. NP, other side is still good.
Initially, I glued a 1" thick strip of pine to a plywood veneered table edge that I built. It started coming off about a month after I built the table.
I removed all the pine edging and then shaved about 1/4" off the plywood table edge to remove the remnants of soaked in hardened glue. Then I tried gluing again with a different brand of yellow carpenter's glue. Same problem happened again about two months later.
All of this seems really strange because after the second try, I glued on a roll of veneer stripping and that's stayed on quite well ever since then.
I can only surmise, that pressure (such as elbows) put downwards force on the table edge. Other than that, to be honest, I'm not sure where the problem lay. Maybe it was me and my technique, the type of glue I used or something else.
That's my limited experience with it. I've never tried again.
Possibly. Much of what we build is dependent on how we've built things through the years. For quite a few years, I used a blind nailer on my face frames, something I bought a long, long time ago from Lee Valley Tools.
Essentially, it's a mini-plane that raises a thin shaving of wood. I'd then drill a slightly undersized hole in that space and drive in a countersunk finishing nail. The raised shaving would then be glued back down and clamped in place for about ten minutes. I produced an invisible method of joining my face frames.
That method worked really well for a long time. Then I bought a Domino and just like the biscuit joiner, I haven't used the blind nailer since.
I've glued hardwood to hardwood, pine to pine and a combination of both and they've stood up well. It's just the gluing of solid wood to plywood edging that I've had this problem. Never could figure out why.
I wish you had pictures so we could help you out better. My first instinct is not tight enough clamping. Long shot, though, since it doesn't take much pressure at all. As another poster stated, just enough to close the gap.
My second is wet wood-- the pine, maybe. Silly question, but was either product pressure treated in any way? Was the pine recycled from another project and treated with any kind of finish or solvent?
I love the blind nailing technique. I don't know who invented it or when, but I think it's brilliant.
In the case of gluing *and* finish-nailing a face frame, I still contend that the purpose of the nails is to act as clamps until the glue dries. Norm used to mention this a lot on his show.
So enlighten me here. I've seen cauls (pictures of them anyway) that have a very slight curve on the surface that will touch the work. Your picture has a much sharper curve at each end than I would have expected, and I can't tell if the middle is curved or not.
My understanding is that the curve on the business edge is to provide clamping pressure in the middle even though the clamps are only applied to the ends. What is the pronounced curvature near the ends of your cauls for?
I don't want to answer for him, but... well, here I go. :-)
You are right about long cauls having a slight curve on the clamping side, and you're correct on the reason for that curve. It would nice if there was a formula for that curve in relation to the length of the caul. Maybe the same guy who did the on-line shelf "sagulator" will do one for cauls.
However, in the case of woodchucker's photo, in that application, the curve is acting like a truss (think steel arch bridge) that keeps the caul straight and able to clamp that distance without bending.
The difference between the two applications is in the former, you want the caul to bend until it's touching all the boards, applying (hopefully) equal pressure. In the latter, you don't want it to bend so it keeps touching all the board(s) allowing it to apply equal pressure.
Nothing pressure treated or finished in any way ~ at least before the glue dried and then I applied a Minwax stain and finish.
It occurred to me that the glue I applied didn't adhere well to the layers of wood already glued together with the plywood. Or maybe, just really poor quality plywood. In any event, it was a number of years ago that I last worked on this and I haven't tried a similar construction since.
Maybe it's time to try again, if only for information's sake.
I always thought, maybe mistakenly that the glue was just to add some extra holding power. And yes, I've read the articles stating that a properly glued wood connection is superior strength to the wood surrounding the joint.
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