Plywood shelves

Re: Plywood shelves

Larry verhff

I would put biscuits in them, because I just do not trust glueing plywood together. I thing putting biscuits or something like them would help hold it. Good luck Larry in north west Ohio

Re: Plywood shelves

al morgan

I would think finish nails would too.

Re: Plywood shelves

Barry Irby

Are you gluing the pieces on to make the shelves wider or thicker?

Not that it really matters. Many years ago I built a storage cabinet in my kitchen that has plywood shelves about 12" wide and close to 40" long. The shelves were salvaged plywood and had delaminated in some cases. I glued them back together with yellow glue and glued a thin strip on the front edges to hide the plies. They have been loaded with groceries for thirty years. What ever flexing has occurred has not been a problem.

Edge gluing to plywood, you really only count the plies that are parallel to the banding, but, if you soak the end grain plies with glue you get some additional benefit.

OTOH, if you add spline or biscuits or Dominoes you will have possibly wasted a little time and effort, but if it never fails you will never know whether that was the saving grace.

Re: Plywood shelves

Yonak

Joe, I'm partial to splines. There's no strength in biscuits.

Re: Plywood shelves

Stuart Hough

Joe,

About 15 years ago I built a short bookcase out of Birch plywood, 3/4" thick. It is 48 inches wide by about 12" deep. What I did was use finishing nails through the back, into the shelves, and poplar strips bout 1 1/4" x 3/4" x 48" long, with a rabbet 3/4" deep along the tall edge. I then glued this to each of the shelves, nestling the front edges of the shelves into the rabbet on each strip. After 15 years, there is still no discernible sag to the shelves, which seem to be loaded with every cookbook known to man. I also use poplar edging along the case edges, to hide the plywood edge. This was my first project, and am happy to admit...I screwed up just right!

Re: Plywood shelves

Dick Coers

When I edge band plywood shelves, I make the 2" the vertical dimension. I cut an 1/8" rabbet in the back of the hardwood, just a bit over the thickness of the plywood. That acts like a ledge to pull the plywood flat if necessary, and helps locate the two parts together for the glue up. A card scraper brings the two top surfaces flush.

Re: Plywood shelves

Jim Dillon

Joe, I favor some type of "support" in your case if for nothing more than help in alignment of your edge with the shelf. Be it a spline, biscuit, domino etc., any help during glue-up is beneficial IMHO. I agree with Dick that a scraper is very useful in fine-tuning the edge/plywood junction. Jim

Re: Plywood shelves

AZ in Colorado Springs

Biscuits may help with alignment when gluing, but won't add any useful strength. With a 2" hardwood banding, those shelves won't sag. As Barry suggested, size the plywood since about half of it will be end grain. It'll be plenty strong.

Re: Plywood shelves

John McGaw

I've done similar things, attaching wider strips to add stiffness and cover the plies, and have taken to using biscuits. They may only add a bit of strength over what you might achieve if the glue coverage was perfect but they do make the glue-up and alignment and clamping way easier. The last ones I did I wound up clamping two shelf assemblies strip-to-strip which cut down the number of clamps needed since the shelves act as cauls for each other.

Re: Plywood shelves

Dave Bair

If anyone has access to the March/April 2001 issue of FWW, I believe biscuits were determined to be the strongest joint over mortise and tenon and dowels in an objective test of joint strength.

Stronger than M/T? I'm skeptical

Dick Coers

Edit; Can't find an easy access to the article, but did read this response on a forum.

I believe you guys are talking about two different articles. In an article in FWW issue #111, pp. 58-61, biscuit joints fared well in stress tests. In another article in FWW issue #148, in a whole different set of tests, biscuit joints didn't do so well.

Joe's application

Bill Tindall, E.Tn.

Joe's engineering need is not like for a leg fastened to a rail. He just needs to keep a solid piece of wood fastened to a plywood edge, which does not provide the most favorable gluing surface. Depending how it is sawed it may provide a crappy mating surface. A spline or biscuits will provide some enhanced long grain glue surface as well as remove flex stress by shelf load from the joint.

Re: Plywood shelves

William Duffield

I just reread that article, "Testing Joints to the Breaking Point" by Bruce Gray, starting on Page 74 of Issue 148. It doesn't at all agree with your interpretation. In their tests, biscuits were substantially weaker than either traditional or loose tenons.

Re: Plywood shelves

Dave Bair

FWW biscuits tests: Thanks for looking it up. I guess what I remembered from 18 years ago was backwards.

Re: Plywood shelves

William Duffield

That's OK. It happens to all of us, in this case especially with the barrage of advertising from the biscuit joiner manufacturers. Note though, that the FWW test put very different types of loads on the test joints than what we are discussing in this thread. Unless you are building shelves to hold your collection of cast iron V-12 engine blocks, biscuit joinery is probably sufficient for this application.

The one time I had a failure trying to stiffen the front of some shelves, it was due to insufficiently glue sizing the front edge of the composite shelf, and not due to choosing an inappropriate fastener.

Re: Plywood shelves

AZ in Colorado Springs

I haven't seen that article, but Wood magazine did a similar type of test, I think about 2007. Prepared several types of joints in several copies of each, then took them to University of Iowa for testing -- compression tests and pulling the joints apart using a hydraulic press. The M&T was the granddaddy of all joints. Biscuits added maybe 15% to the strength of a butt joint or an edge joint.