Hello everyone, and thanks in advance for any advice you may have to offer a newcomer like myself.
I’m attempting to design two identical 4′ x 4′ Walnut tables. The design would be similar to a casino table with an armrest and a lowered area in the center. The goal is to have the ability to remove one edge from each table and put them side-by-side into a larger 8′ x 4′ configuration.
I have a plan, but am concerned about the strength of a joint between the horizontal armrest (~4-5 inches wide) and the vertical side of the table. It’s shaped like this:
===== 1″ Horizontal Armrest
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|| 1″ Vertical Table edge
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Problem #1: If I’m understanding correctly, it seems impossible to align the grain directions at the joint (due to it being 4′ long and joined at 90 degrees). How much should I be concerned about that?
Problem #2: Assuming the armrest and table edge are joined using a full-blind dovetail (~1/2″ width/depth) and that there are some 3/4″ thick triangular supports underneath (crudely shown below), does it seem like it would be sturdy enough to support an adult (or 2) leaning on the armrest?
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Please let me know if I’ve omitted any details that would be helpful.
Thanks again!
Replies
I don't understand the grain matching problem. If the table is square, just rotate the tops until you find an aesthetically pleasing match.
To the second point, I think it will work if you have several (I would go with at least 4 placed at 6, 18, 30 & 36 inches) on each side. I would also be sure the joinery is solid connecting the brace to the rail and edge. Barring crazy abuse of the rails, they should be solid enough. Just let people know if there is any dancing on the tables, stay off the rails.
Ha! I'll make sure to keep the dancers off!
Thanks for your thoughts.
For the braces, I was thinking about a stopped sliding dovetail to connect them to the edge.
Regarding the grain -- it's an area that I am thoroughly confused about and may be overthinking. I figured there would be no way around the grain causing expansion/contraction of the armrest in the horizontal direction, while expansion/contraction of the table edge would be in the vertical direction. I'll keep studying!
As to problem #1, you have no issue to be concerned with. Both boards have the grain running in the four foot direction. The fact that they are at 90 degrees to each other is irrelevant. Perhaps you are thinking about cross grain construction issues, but that's not what you have.
How are you going to join the sides and top at the corners?
Also, I don't understand how to use blind dovetails to join the sides to the top. Use a spline or biscuits instead.
Sorry, I misunderstood the grain question. I would definitely make the screw holes over sized to allow for movement. Not sure which direction your screws will go, but you can use slots or just oversized holes. With a 4 foot wide slab, you may need to account for a fair amount of movement based on where you live. A good rule of thumb is 1/8th inch per foot across the grain.
Looks more than strong enough to me.
If you think about it, you might use 3/4 inch material as flooring. Provided it is supported at 18 inch centres, it will survive being used for that dance...
TBH, the dovetail idea is probably overkill, but would work well. If you are clever, you will not get wood movement issues. I am assuming you want a solid side for the table. In this case, just put an additional rail across where you want the arm rest to be and attach it to that - the grain direction on the rail is the same that way. It means you have two panels to make, which sucks, but it would be much more solid construction.
By the time you have engineered for wood movement, it would be quicker to do the extra panel anyway...
Thanks again!
I hadn't seen/heard the rule of thumb for movement. I'm in the Midwest, so, theoretically, if the armrest is 4-5" wide, I'd want to allow about 1/16" of play in the joint if I do this in the winter, but something less if I do it in the spring/summer. Does that seem about right?
Rob, I'm interested in what you were saying about an additional rail, but am having trouble picturing it in my mind. What did you have in mind for where the rail would be placed, and how would it be oriented?
If you go with your sliding dovetail (a favored joint by me) you can deal with movement by only gluing the first inch or so on the vertical and horizontal where the edges meet. The balance of the length is left free to expand and contract as required.
Thanks Gee -- that makes sense. Based on the responses, I'm thinking the full-blind dovetail would be a mistake in that joint, and that I need to allow those two boards to "float" more. I'm also thinking that the braces underneath (sliding dovetails), will provide all of the weight bearing support necessary.
Would a rabbet be a more appropriate joint between the horizontal and vertical boards to allow freedom of movement?
Thank you.
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