Bench apron/rail question

[Bob Grier]

I am about to build an 18" high by 5-foot long solid wood entryway bench that will have top storage accessed through the hinged top/seat/lid panels, similar to a piano bench. Storage under the seat will be about 8" deep. The front and back top rails/aprons will need to support the lid without much deflection when 2 people sit on it. I would really like to use solid 3/4" or 7/8" thick apron full 8" wide to reduce deflection to the minimum.

However, I am aware that just gluing the solid apron into the legs with mortise and tenon joints would likely be a problem due to moisture expansion. The way around moisture expansion/contraction would be to use narrow maybe 2 1/4" wide rails with floating solid wood panel or glued plywood panel. I don't think floating panel would be appropriate here because the top rail would probably deflect more than I would like when people sat on it. I am thinking of using plywood panel glued to the rails or just using plywood for the aprons but would prefer solid wood.

Another thought is to use a solid wood apron connected to the legs with tenon only at top 2 1/4" and let the remaining apron below that just float up and down against the leg or inside a shallow mortise in the leg. I think 2 1/4" tenon would be adequate for the shear but I expect there would be a problem with racking. It would be nice to connect the bottom of the aprons to the legs in a way that allows the bottom of the apron to float up and down on the legs but held tight against the legs to counteract the racking forces. I hope there is a simple solution to that detail. I am often amazed at how there are simple solutions to things I can't figure out.

I used on-line calculator to estimate moisture movement in 8" cherry and came up with about 1/16" for my location. I think that is enough to cause something to break but maybe the wood would compress and stretch to accommodate it. I don't think so though.

I can't make a decision on what to do.

[David Utterback]

About 15 years ago, I made a cherry version of the G&G Blacker House entry hall bench which has a similar storage compartment. The double tenons on the aprons have held up well. IIRC, they were about 2" wide and 1 1/4" long. Let me know if you need further info.

David

[Jerry Miner]

In an 8" apron, your expansion/ shrinkage issues likely will be minimal, but to be safe, you have options:

If you use plywood for your aprons, the expansion issue disappears, of course.

A frame-and-panel apron (as in your drawing) will essentially eliminate the expansion issue also, but may not be the look you want.

If you want to use a single solid cherry board for the apron, you can cut a double tenon, glue the top tenon, and use a peg in an elongated slot in the lower, unglued tenon (in an oversized mortise)---like a breadboard end on a table (you will want to offset the holes for the end aprons):

8 inch apron 10-22-16.jpg

[Bob Grier]

Thanks David and Jerry,

David - In your bench, did you pin one or more apron tenons to accommodate movement? I am thinking about glue one tenon and pin the others

Thanks,

Bob

[Wayne Lomman]

Just do it with the double tenons and glue. I make doors all the time with 300mm wide bottom rails and there is no problem. They have way more variations in environment. Cheers

[David Utterback]

The tenons were glued without pins. A pin would not hurt but may be unnecessary as Wayne says.