Can anyone help me to solve a problem in protecting the edge of veneer? I have searched through a half-dozen books and can’t find a solution to this problem.
I am designing some casework with plywood body and veneer facing. Where two panels meet, the outside veneer edge of both panels will be exposed to damage. I would like to have a thin, narrow strip of hardwood protect the veneer edges. However, the thickness and width of the hardwood strip reduces the amount of overlap of the panels themselves. So I am concerned about the strength of the glue joint there.
Perhaps this diagram will help explain. If the panels are 1/2″ thick and the hardwood trim strip is 1/4″ wide and 1/4″ thick, then the gluing surface for the panels is only 1/4″ wide. I am concerned that this will not be strong enough. I don’t want to go to a thicker plywood because the finished piece would be too heavy.
Can I count on the 1/4″ gluing surface of the hardwood trim to add strength? Would it be stronger if I glue the hardwood first on one panel and then rabbet the edge to mate with the other panel? Or is there a better method to protect the veneer edge?
Edited 2/11/2006 10:44 am by JohnH
Replies
Similar to cockbeading a drawer which was often done to protect a veneer face as well as add a decorative touch.
A glued butt joint between two pieces of plywood isn't going to be satisfactory, with or without the facing strip, I don't think. There needs to be a mechanical fastening of some kind, whether biscuits or dovetails, or even my least favorite Kreg screws.
Perhaps you should give a few more details on the project and what kind of plywood you have in mind so the forum members can chime in concerning the joinery and protecting the veneer edges. Lots of knowledgeable people here and no flames either.
Hello Steve,
I would appreciate your opinion on the solution that I proposed to JohnWW, above.
I'm still troubled by this joint. The blue board has only plywood ends in its glue surfaces, either on itself, or on the mate. Those are inherently weak since a half of the joint is end grain, which should count very little. And half inch ply is quite thin for what seems to be a large box. You say 3/4" would be too heavy, which implies the box is destined to be moved around. That calls for strong joinery. Why not consider JohnWW's proposals. They seem pretty much like a minimum to me, though I still don't quite understand the big picture of what the purpose of the box is, and what the rest of the box will be.
Steve, Please see my apology to you and JohnWW and a better description of my question, above.
My suggestion is to do the mitered joint reinforced with biscuits. This will provide adequate strength, will protect the corner, will give you a new skill, and is relatively easy.See attached.
Hello Sapwood,
Thanks for the suggestion and the diagram. I will be fun to learn something new.
Hello sapwood,
You are right! Mitered joints in 1/2" plywood are strong. Actually, instead of reinforcing with biscuits, I used splines as in Lon Schleining's article in FWW #181 Winter 2005/2006. First, I made a test piece. For a one foot long joint, it withstood 200 pounds of axial load in the plane of one panel and 200 foot-pounds of torque in the direction of opening the joint. I expect the strength in closing the joint to be greater.
Hi JohnH & JohnWW,
I must confess. I was helping another poster (plywood cubes, hiding edges) and I recalled Lon Schleining's article in FWW #181 and thought it would solve his problem. Little did I know that you were needing a similar solution!
I have every issue of Fine Woodworking and remembered reading the article, as I am outfitting my bench with storage cabinets using the same process that Mr. Schleining used.
Best of luck,
Bob @ Kidderville Acres
Kidderville, NH
Use whatever tool needed to Git 'r Done!
Steve, You might be interested in the actual strength of a splined miter joint in 1/2" plywood posted above. Many thanks for your thoughtful suggestions.
Reinforce this joint with biscuits and it will be fine. Remember, the edge lipping is held on with glue so it also contributes to the joints strength.
When working with plywood the whole shebang is about a reliance on glue, so go for it. Trust the glue.....
Have you considered using a miter joint here? It could be unreinforced or reinforced with biscuits, a spline or glue blocks depending on what you are making. Make a test piece and then break it apart after the glue has dried to see if it will be strong enough for your application. I have made large cabinets with unreinforced miter joints and have found them to be quite strong when done properly. I would protect the outside corner with a strip of hardwood 1/8" X 1/8"
As suggested, here is more detailed information. The plywood is Baltic/Russian/Finnish birch at 1/2" thick. The joint is 32" long and joins two panels of 18" and 33" width respectively.
Regarding biscuits, is there enough room in the 1/4" deep rabbet? Or am I not understanding the suggestion?
A miter joint is interesting, even if I can't hold the cuts true over the 32" length within 1/32", sawing off the point to accommodate the hardwood trim could cover up my less-than-perfect craftsmanship.
I'd suggest going back to rethink the design, there is very little strength available in a long 1/2" plywood to 1/2" plywood joint no matter how it is built.
At a minimum, you need a wood strip inside of the joint that the two pieces of plywood can attach to for additional strength, or perhaps something like a corner post with rabbets down two sides to set the edges of the plywood into, which would also protect and hide the edges of the plywood.
John White, Shop Manager, Fine Woodworking Magazine
Hello John,
Thank you for your advice about rethinking the design. I would appreciate your opinion on the joint in the diagram. My thinking is to rabbet both plywood panels about half their thickness, glue them together, then glue a 1/4" x 1/2" hardwood strip into the exposed rabbet. The resultant joint is a dado-and-rabbet as described by Doug Stowe on p. 33 in Box Making from Taunton Press. At the same time, the hardwood strip protects the edge of the veneer face on the plywood.
To add strength against the tongue pulling out of the dado (left-to-right in the diagram), I may cross-fasten it with the small ends of Miller mini-dowels, excess cut off flush before applying the hardwood strip.
John, Steve answered ahead of me and I can only echo his opinion. The new joint has very little surface and some of it will be end grain which will create a weak glue joint. A more basic problem is that there just isn't enough material in the plywood alone to create a sturdy joint. No matter how you glued the two pieces of 1/2 inch plywood together, the joint would still be weak in an assembly this large. Cutting into the joint to add a trim strip makes the joint even weaker.If there is no strain, or flexing, and no load on the joint you might be able to use it but the connection will be relatively fragile. John
John and Steve,
Many thanks for your replies. In my thirty years of experience in new product development I was always frustrated by the inadequate description of the customer's problem. And now I am guilty of the same thing!
The joint in question is that between the back and side(s) of a cabinet/chest of drawers that holds the accessories for my table saw. Because of my particular situation, it must roll up and down a small ramp, hence the concern about weight.
The key factor that I am ashamed to admit that I left out is that there is a top and a bottom to the chest/cabinet. These will be attached to the back and sides with glue and dowels. So there won't be any significant stress to swing the joint open about an axis along the joint.
The stress that I am concerned about is the back and/or sides flexing like a billowing sail and pulling the joint apart near the middle of the seam.
Again, I apologize for an inadequate description and would appreciate your opinion about this joint with this new information.
JohnWW, You might be interested in the actual strength of a splined miter joint in 1/2" plywood posted above. Many thanks for your thoughtful comments and suggestions.
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