Question on Plywood Rabbet Joints

[kwc]

Hello,

I'm building a small bookcase (my first "large" project) out of 3/4" cherry plywood. I've rabbetted the tops of the side panels (3/8" depth, flush to top) and intend to sit the top into that panel.

My original intent was to only use glue in the joints without any fasteners. Is this a bad idea? If not, which would be the better option -- finishing nails or screws, and should they go into the side or approach from the top? Recognize that I'd be inserting into the grain of the plywood in both cases.

Thanks!
kwc

[LarryG]

Glue alone will be sufficient. I built some bookcase-like CD and DVD storage units out of oak plywood in which the only mechanical fasteners were some 1/4" narrow-crown staples to hold the back panels in place. Everything else was rabbets, dadoes, and glue.

Just remember that plywood end grain will really soak up the glue, so be sure to use plenty and not starve the joints. I recommend lightly sizing the joints first and then applying the actual glue that will hold everything together.

[LCHIEN]

Glue alone will be sufficient. I built some bookcase-like CD and DVD storage units out of oak plywood in which the only mechanical fasteners were some 1/4" narrow-crown staples to hold the back panels in place. Everything else was rabbets, dadoes, and glue.

Just remember that plywood end grain will really soak up the glue, so be sure to use plenty and not starve the joints. I recommend lightly sizing the joints first and then applying the actual glue that will hold everything together.

if you're not familiar with the terminology, sizing the joints means applying a thin film of glue to the surface of the joints and allowing to dry thus priming the joint for better adhesion (because so much glue won't be soaked up by the wood).

[cabinetman]

Hello,

I'm building a small bookcase (my first "large" project) out of 3/4" cherry plywood. I've rabbetted the tops of the side panels (3/8" depth, flush to top) and intend to sit the top into that panel.

My original intent was to only use glue in the joints without any fasteners. Is this a bad idea? If not, which would be the better option -- finishing nails or screws, and should they go into the side or approach from the top? Recognize that I'd be inserting into the grain of the plywood in both cases.

Thanks!
kwc

I'm trying to visualize what you are doing. If the rabbet is 3/8" deep into the side panel, and it's 3/4" down from the top to accept the top plywood, you will see the top edge (3/8") of the end panels, yes/no?

Yellow type glue works very good on porous surfaces. If you get enough glue into the joint , clamp up the joint, and get some squeeze out, that would be sufficient. I'm not an advocate of "sizing" because it lessens the porosity of the plywood joint, IMO.

Of course some type of fastener would always help, but a good glue up and clamping is sufficient. On finished surfaces where a finish nail is necessary you could "blind nail". That is a procedure where you use a sharp knife, and lift a section of the wood very carefully, then put in the nail, set the nail, and then replace the wood section with glue for an "invisible" type of fastening.

[Larryl]

All replys have been absolutely correct, and I may be stating the obvious... be sure to attach a back to prevent "racking".

[drumpriest]

One point is that plywood is about 1/2 long grain and 1/2 end grain regardless of edge direction, due to the plys being laid in opposing grain directions to ensure a stable piece of wood.

Another is that if you are really worried about the strength, you can do a "reenforced rabbet". Basically glue it up as you say, then drill a dowel hole through the joint, and glue in a dowel, flush trim and sand. I have done many of these, with an opposing wood tone, decorative and strong.

[kwc]

Thanks to all for the recommendations. I think I'll stick with just glue for this project--sounds like the consensus is that this should work fine.

Cabinetman: The rabbet depth is 3/8", but cut 3/4" down into the top edge of each side so the top is flush. My description wasn't very clear.

Thanks again,
kwc