I have read that a well cut and fitted dovetail joint does not need to be clamped — assemble the joint, check for square, and set it aside.
To me, it seems the same could apply to biscuit joints used in plywood cabinets. As I understand it, the real strength of a biscuit joint is derived from the swelling of the biscuit when glue is applied, and therefore should not require clamping.
Has anyone tried this and if so, what were the results?
Replies
This is basically true, once the biscuits swell they'll lock the joint tightly together, but it takes a few minutes for this to happen. Also, in most cases, clamps will be needed to pull the joints together initially.
John w.
I tried it last night on a 36" x 28" x 12" wall cabinet and it worked great! As you mentioned, I used clamps to snug the joints, left them on for about two minutes (I am using Titebond II slow set glue -- I still need a stiff drink after a glue-up, but at least I can hold the glass without spilling anything), removed the clamps, checked for square and called it a night. There was no separation at the joint line. I don't think I'll ever go back to clamping down and leaving the clamps on, unless it the project is more complicated than a box.
Thanks for the input.
"I still need a stiff drink after a glue-up, but at least I can hold the glass without spilling anything)...." Too funny! Glad I'm not the only one, and I've not even done any fancy casework yet.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)Another proud member of the "I Rocked With ToolDoc Club" .... :>)
I've read your posts and re-read them and keep wondering: why the rush to take the glue-up out of the clamps? Biskets primarily aid in alignment, especially on solid-wood panels; in plywood, there may be some justification to say they add strength as well. Biskets don't have little gripping fingers in them that hold the joint together; that's the job of the clamps. When I have a glue-up like that to do, I plan my day and do that first thing, then move on to other parts of the project; other times, I might do a panel glue-up at the end of the day and leave it overnight. You can't rush a good glue-up or good bourbon!Bill Arnold - Custom Woodcrafting
Food for Thought: The Ark was built by amateurs; the Titanic by professionals.
Regrettably, I have very poor glue-up technique with plywood boxes. It seems that no matter what I do with the clamps I always pull something out of square and have to correct it. I was looking for a simple way to solve the problem.
Believe it or not, I don't have a glue-up problem with furniture, such as tables or night stands, etc. I suspect that the problem with plywood is the size of the box.
I suspect that the problem with plywood is the size of the box.
What size boxes are you building? I assume the box has a bottom or back (depending on your point of view).
In any case, one way to be prepared for your glue-up is to have a clamp or strip of wood long enough to reach between diagonal corners of your box. If, while clamping during glue-up, the box gets out of square a bit then use a clamp across the diagonal with the greater distance and pull it back until both diagonals are the same. A strip of wood can be used for the same purpose if you can nail it into the edge of the material. When the diagonals match, leave the item alone while the glue cures.Bill Arnold - Custom Woodcrafting
Food for Thought: The Ark was built by amateurs; the Titanic by professionals.
Thanks. It seems that applying a diagonal clamp just makes things worse. I never thought of using a strip of wood. I'll give it a try.
DanT,
I use biscuits for several types of projects and I have had terrific success with them. But I find that biscuits can be a little stiff going in, and need clamping pressure to assure a clean fit.
On needing a drink after glue-ups, I know just how you feel! Recently, I started a discussion on this very topic!
Go here to see it:
http://forums.taunton.com/tp-knots/messages?msg=17103.1
Yes, I read your post when it was first posted. I have switched to slow set glue for the reasons mentioned. So far, I have had good results.
I agree with John. You need something to hold the piece together until the glue dries.
Nails or screws will work, otherwise use clamps.
Thanks. Please see my post to JohnW.
I always clamp my biscuit joint glueups for at least a couple of hours - preferably overnight. I'm not sure that "a couple of minutes" is enough time for the glue to take a good set.
One thing I've found is that the clamping should be just tight enough to hold the joint in place. I go for a small amount of squeeze out over the full joint and wipe it off with a damp rag.
Depending on where the joint is in the structure, it has to withstand either tension or compression and possibly torsion (twisting). With a butt joint in compression, all the biscuits do is aid assembly alignment because the wood properties provide all the strength. If the joint is under tension, the total bond strength of the entire glue area keeps the joint in tact. If you don't glue the two faces of the butt joint as well as the biscuits or don't apply appropriate clamping force, the glue won't penetrate the wood well enough to form the best possible bond for the area of the butt joint. This area is typically much greater than the glue area around the biscuit itself so you can end up with a much weaker joint. In a torsional situation, the strength of the glue area of the butt joint as well as the shear strength of the biscuit itself keep the joint together. Again, not having a good bond between the two pieces of the butt joint really weaken the joint.
This is all fancy engineering talk for saying that even though biscuits do add strength to a joint, clamp the joint as if they never existed.
Dear Dan,
Many good replies supporting clamping.
Yes, to all. When the buiscuits expand, they will do that going back to their nature. They are compressed when built. When they expand, they will move whatever they touch and can be moved due to expansion, even if minutely. The buiscuits fibers go at 45 degrees from their longer axis in order to counter best shearing forces and the wood for that is weaker along the fibers, which means the joint-line too. So, when they expand, if they are not clamped, they could and would minutely separate the joint and spoil it. Of course there are many other factors such as size and shape of work-piece, wood or material type, joint-quality and matching of the wood or material, and material perfections or imperfections.
The other thing would be to put benefitial presure for the glue to go into the fibers of the wood as soon as possible, favoring absortion by osmosis. If one waits too long to clamp, the glue may not absorb as well, with factors also as temperature, humidiy of day, and of wood having to do with absorption, but pressure is always pro-absorption, provided it wouldn't be excessive.
The glue by itself is not really 'stronger than wood' but it is the combination of glue dried on wood-fibers which is stronger. A tite bond (not meaning the brand) favors that.
Also, it is not quite true that the buiscuits are limitted to alignment function. Since their fibers are at 45 degrees, they do provide more counter to shearing at the joint, as said above. If they were good enough only for alignment, then why put glue on them?
All above is on yellow or white glue basis, which are considered not to have much gap-filling capability.
Good luck on all.
-mbl-
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