Joinery Question - Mixing Plywood to Solid Wood Panels

[Brad Pearce]

Fellow Creekers -
I am designing an entertainment center and am having difficulty in deciding on all solid cherry or a mix of solid cherry and cherry plywood. I would prefer this to be as authentic as possible so I am leaning towards solid wood. The conundrum comes from potential wood movement. A series of SketchUp screenshots below provide the general picture. There are raised panel pocket doors with a removable "box in a box" to access the hardware. Dimensions 61" long x 22 deep x 32" tall. Issues:

1. My concerns are the side raised panels where the wood grain is in mixed directions versus the interior panels where wood grain is vertical. Would this cause humidity related stresses beween the two types of panels? I guess that an externally hung side panel is a possibility to complete the look.
2. Is a single top panel adequate [1" thick] or should I go with a 3/4" top to finish the case then a final slightly larger 3/4" top?
3. For joinery I was thinking case dados, face frame splines & pocket screws [where appropriate] and a couple of dovetail joints in the front apron. Should I being doing this differently?
4. It is tempting to use cherry plywood for the interior case sections but the joinery would have to allow for differing wood movements. Probably a bad idea?

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[Jamie Buxton]

My concerns are the side raised panels where the wood grain is in mixed directions. Is this possible using all solid wood construction? I guess that an externally hung side panel is a possibility to complete the look.

Yes, frame and panel construction evolved to deal with solid wood movement. The panel floats inside the frame, captured in dadoes, so it can expand and contract.

Is a single top panel adequate [1" thick] or should I go with a 3/4" top to finish the case then a final slightly larger 3/4" top?

1" is structurally sound. However your case construction may be easier with a subtop.

It is tempting to use cherry plywood for the interior case sections but the joinery would have to allow for differing wood movements.

Here is the deal... Plywood does not expand and contract in either direction. Wood expands and contracts across the width, but not the length. It does this in response to changes in atmopheric humidity.

By making the end panels frame and panel, you've established that the ends of the casework are not going to expand and contract. This means that all the other major panels in the case must also not move. You could make them all (bottom, top, interior walls) frame and panel, but an easier way to do it is to make them all plywood. The on the top you make the subtop plywood, and tie it tightly to all the vertical panels. The real top could be solid lumber, for good looks. It would be tied to the subtop in a way that allows some expansion and contraction.

[Sam Murdoch]

If I were doing this - unless I truly intended a solid wood cabinet - I would build 2 interior boxes with 3/4" plywood sides, bottom and shelves, out of cherry or a prefinished maple.

The sub top would be 2 rips of 3/4" ply x 3" wide in each of the 2 sections to support the solid wood top.

The back would be 1 full 1/2" ply that would span both interior boxes.

The exterior sides would be the 5 piece frame and panel that you show, using either solid wood for the panels or plywood.

The top would be the solid wood top as you suggest.

The doors would be set into a wood face frame that can be biscuited or pocket screwed to your plywood parts and incorporated to your 5 piece finished ends with a simple miter (glue and fold with tape).

All would be set on a base with perimeter trim and detailing as you show in your last drawing. The two exterior sides would overlay the ends of your plywood back.

All wood movement issues would be accommodated if you secure the solid top to the interior stretchers through elongated holes.
All the interior parts create no problems in this regard. The shelving holes are all in plywood sides, not mixed and matched plywood to frame and panel as you show in your sketches.

The ventilation through the back would be much less elaborate - merely a wood louvre or some store bought louvres intended for such cabinets available from Lee Valley, Woodcraft, Doug Mockett etc. Wire management too from these sources.

If you want a solid wood cabinet, please disregard the above . New post required. Meanwhile, hope that this offers a workable process for you.

Sam