Hello all,
I am making a simple set of shelves out of 3/4" plywood with the shelves attached to the sides with biscuits. My question is: Do I need to put glue on the ends of the shelves in addition to the biscuits, or will just the glue in the slots work good enough?
Thanks in advance,
Ronnie Aldrich B'ham, AL
With most any joint of this type, glue on all mating surfaces is stronger than not.
With plywood, glue _both_ the edges, and the biscuits, before clamping.
I have made joints with glue only on the biscuits just for fun and they have been plenty strong. (In fact I have used just water and they have been pretty good.) Since you will have mainly shear stress, it ought to be fine if you don't want to glue the ends for some reason; especially since end grain gluing isn't worth much anyhow.
Is there a reason you don't want glue on the ends?
Ronnie Aldrich asks:
Biscuits are primarily alignment devices, adding very little extra strength in most cases. Add glue to the end of the wood, too, as well as to the slots and the biscuits.
Charlie Self "Half of the American people have never read a newspaper. Half never voted for President. One hopes it is the same half." Gore Vidal
It's actually more important that glue be spread across the mating surfaces than in the slots. Biscuits will aid in alignment but add little strength. mahalo, jo4hn
Hum...I would use polyurethane glue (gorilla glue, etc), and, would glue the end of the shelves as well as the biscuits. However, since I am distrustful of shelves...I would also put a slight dado (1/8" or 1/4") into the sides and inset the shelves into them, and, skip the biscuits entirely. If you put a back on the shelves, your plan will work ok. However, if no back, then the shelves may rack a bit, and break the shelf to side joints loose...dropping the shelves out. Actually, I also just think that butt joints like that are kind of ugly, and I prefer the dado look...and it IS a lot stronger and stiffer. Regards Dave Mundt
Mix of answers, what? The biscuits resist shear - the downward weight of the books, in this case, very well. They don't do as well against racking - the bump on the top corner or the attempt by someone to drag the case on one end while partially unloaded. That is best served by a full back, fastened to both sides and shelves.
The glue on the shelf ends would help a bit in keeping the joint butted square and tight, aiding in both shear and rack. Probably won't be much, but wouldn't hurt, certainly.
snipped-for-privacy@aol.comnotforme (Charlie Self) wrote in news: snipped-for-privacy@mb-m11.aol.com:
Can I disagree here, Charley, without starting a religious war?
In this case, I believe these are much more analogous to a floating tenon, and that what is being made here is much closer to a housed joint. The added shear strength is important.
If we were discussing edge gluing, we would agree.
Patriarch
patriarch responds:
I'd like to test that some day when I have time. Not this year. But three or so biscuits in the end of a 12" wide shelf do not seem to me to add anything much to overall strength, though they do add a little. That doesn't reduce the need for glue on the end of the board where it meets the vertical side of the shelf carcase.
Charlie Self "Half of the American people have never read a newspaper. Half never voted for President. One hopes it is the same half." Gore Vidal
Wow, did you get some replies that hit most of the possible range! Maybe we can look into this a bit more. Now, gluing end grain to face will be a very weak glue joint. And if the end grain is plywood, it'll tend to be even lower density and even weaker (depending on the plywood being lumber core, hardwood ply, or mdf core). Also, any even small racking in the frame will likely break that glue joint.
While biscuits are primarily used for alignment when edge gluing, that's not the only way they can be used. Adjustable shelves, for instance, can hold quite a bit of weight with even a 1/4" dowel used in four holes at or below the ends. That's because you're relying on the shear strength, which is pretty high. If your shelves are fairly tight fitting, I would suspect a biscuit would have about the same shear strength, and that the shelves would hold up with nothing but dry biscuits in them (assuming the frame prevented racking).
Gluing the biscuits adds little to the shear strength, but holds the edge of the shelf against the face of the side, helping to stabilize the frame against racking. I suspect the strength of this joint is such that gluing the sides won't help significantly. Of course, it really won't hurt, either.
For more information on this subject, try it at home. Prototype a shelf with dry biscuits and load on alot of weight. If the shelf's a couple of feet long, I'll bet it bends first. Then take two plywood scraps and glue one to a face with biscuits, and the other just with glue on the edge. Let dry overnight, then break each to see the difference, and conclude for yourself if it's worth gluing the edge.
BTW, remember that you are free to use as many biscuits as will fit, and four on an edge are much stronger than two, of course.
GerryG
Not without a dado/groove, eh? It appears he was talking butt joint to me.
Dang, I better change professions.......all of my work is about to fall apart...
snipped-for-privacy@aol.comnotforme (Charlie Self) wrote in news: snipped-for-privacy@mb-m26.aol.com:
That's true.
I'll admit also that my tendency is to find a means of hiding some of McFeeley's best in there as well. Over-engineered, since these things tend to get overloaded. And somewhat abused, when moved around, during the course of life.
The last set has pocket screws, biscuits, glue, and "brads 'til the glue dries." Won't likely end up in a museum. Might not even sell in a yard sale. But it's holding up 6 cases of engineering texts right now in my office, and is 'seismically stable'.;-) I needed it quick, since one of the kids needed to move back home 'for a while'.
What's Brother Roy say? 'Twill do. 'Twill serve.
Patriarch
"Swingman" wrote in news: snipped-for-privacy@giganews.com:
What I was thinking was a constructed mortise and tenon. Perhaps I used the wrong term. Wouldn't be the first time.
Well, you surely won't be alone. All the people who've driven a nail or screw into the edge of a shelf will be right behind you.
Actually, just happened to be read>>
Hello Ron,
Are the shelves for Video Casettes for your business or something heavier? Providing additional glue to the edge and face of a 90' plywood joint without a dado or T&G joint will fail over time. Using Lamellos with glue may be sufficient ( and probably will be). Please note...the potential of glue "squeeze-out" may compromise your possible intentions of staining the shelving unit(s) Clean up that excess glue.
BTW...Opps. I just read through my post prior to sending and saw that I used the word Lamello. It's a brand name from the Swiss who developed the first biscuit joiner machine I think. Most folks look at me funny in the shop when I ask them to fetch the #20 Lamellos...LOL Good Luck Ron.
The only reason I have for not wanting to glue the ends is so I would not have to deal with glue squeeze out.
Thanks for all you help.
Got a table saw and dado set, or a router with a guide? It's pretty hard to beat a dado/groove for non-adjustable shelves in bookcases and cabinets. ("housed" joint, patriarch ;>) )
A simple blind dado/groove is hell-for-stout, will hide the joint, and it'll last until your grandkid's grandkid's cows come home.
I can believe that! I was looking at some of the practice joints in the scrap/firewood box that I did while learning to use the biscuit jointer and they will NOT break loose as my old "screw & glue" or "dowel & glue" joints do...
A problem with biscuit joints at my current skill level is that the mistakes and rejects could out live me...
Mac
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