Alternate to a mitered corner on table top?

[FS7]

What you described initially is something I did and is still holding up well. Seven years ago, when my skills were considerably less (like a 5 instead of a 10 on a 0-100) scale I made a coffee table top like this.

I found a really, really nice figured maple board at Home Depot and made a mitered frame out of it. It was a 1x6 and the coffee table was about 2'x4'. The miters were attached with pocket screws. This gave me a frame of sorts. I filled the inside of the frame with a walnut/figured maple/walnut orientation, also of solid 1x lumber and also pocket-screwed together. Wood movement says this should not work well at all.

The way I generally attach tops is to attach them through 1x2 (or 1x3) that are attached to the legs with pocket screws. So if you envision four legs that are about 1.5" square, there is a 1x2 running in a square pattern from each leg to each adjacent leg. The pocket screws holes face the table top, so all you would see is the screws holding the table top in from beneath. It's a clean-ish look. Because of all the pocket holes underneath, I screwed a piece of 5mm plywood to the underside of the table top (inside the 1x2 mounting frame). This may help.

It's been seven years and two homes, and it's holding up very well. The miter is as tight today as it was back then, and the only discernable change might be a very slight bulge on the middle panel. I do not know for certain that it wasn't there when I made it. I sealed all sides and I keep my home relatively constant in terms of humidity - whatever the AC does in the summer, which is about 50%, and then a whole-house humidifier set to 45%+ in the winter. I do not have any major problems with humidity swings, which is probably why it's held up.

I am not sure what this really means. It shouldn't work as well as it does, and I can speculate as to why. Perhaps that board is exceptionally stable, maybe it's the humidity being relatively constant, maybe it's the plywood, and maybe it's all three. It *can* work but that doesn't mean that it will.

[jteneyck]

What it means is exactly what you said; the RH has remained pretty constant.  Wood doesn't move when the RH stays constant.  But the table would likely not look so good with no AC or humidifier which would let the RH go from probably 30% in the winter to 75% in the summer.  If you expect the RH to be equally constant in the future, go ahead and make those big mitered corners you asked about.  Most of us aren't that brave, however, and I suspect you might not be anymore either or you wouldn't have started this thread.  The two best approaches I've seen so far are:  1) to use veneered plywood or MDF with solid edge banding so you can make 45 deg. corners, or 2) to make a butt jointed frame wrapped with a narrow mitered frame around that.  

John

[Willyou]

I agree with the above in that the mitered frame is not the problem. Having said that, I think I would narrow it down as much as you can while maintaining your aesthetic preferences. I agree that the interior panel is where the potential problems are. You will need to make that panel float within the outer frame. Or, make it with MDF and 1/8" veneer. Also, as mentioned above, I think the best approach is to make the whole top of MDF and 1/8" veneer with a narrow full thickness mitered frame. A top made this way should be very durable and much more stable. Veneers are usually most vulnerable at the edges. This would be mostly overcome with the solid edging.

Be sure to put and equal thickness veneer on the bottom as well. It can be all the same species like poplar or oak.

[jgourlay]

Question is, how is the centre of the table going to attach? That's where the movement will occur, and the solid wood panel (glued up chess board?) can certainly move seasonally. And if it expands too much, it will bust ANY mitred corner open, no matter how it's constructed. 

Only way I can see this working is if you "float" the middle panel in the frame. Then the central panel is free to do it's own thing, and there will need to be a small gap around it to allow the movement. The outside frame wont change in the 3ft dimensions, only the 7" ones, which will be small, and both sides of the mitre will move about the same. So at that point how you join the mitre isn't so critical. Splice, tenons, biscuits, T&G etc.

The center panel won't be a problem.  It's a 24" square, 2+" thick piece of MDF veneered over.  It's held up fine for about 5 years.  I'll sink it ~ 1/4" below the table top, and put a 1/4" glass insert on top. The board will be held up by some separate structure that will allow me to level it, and transitioned with little pieces of moulding:  it won't move and will accomodate all kinds of frame movement.

[jgourlay]

https://www.woodcraft.com/blog_entries/breadboard-ends


There is nothing particularly "rustic" about this table with bread board ends:

https://www.1stdibs.com/furniture/tables...lsrc=aw.ds

True, and they look great on rectangles.  This table, however, is a square--I think it would look funny.  But maybe not.  I need to lie back, shut my eyes, and really visualize it.

[jgourlay]

The issue with your original design was that 7" wide boards were approaching the widths where seasonal movement may be an issue for mitered joints.

The simple solution, then, is don't use 7" boards.  
Rip the boards, then reattach them with a joint that will accommodate some movement.  
Something like a shiplap or tongue-and-groove, pegged, in slightly elongated holes.
Then your outside boards will only be a couple inches wide and expansion and contraction will be minimal.

So, you will actually have two frames around your playing board.
The first, either mitered or butt, and the outside frame mitered.
Maybe a strip of inlay to highlight the joint, since it may be noticed anyway, and the inlay will draw attention the the inlay itself and not to any gap in the joint if it moves.

The total movement over the 14" width of those boards will be the same, but the bulk will be absorbed by your transitional joints.  Your miters will stay tight.

I like this idea.  I need to really think about what kind of inlay would make that expansion joint a decorative element in the context of the whole design.  I'll post a picture and get your ideas.

[Willyou]

The center panel won't be a problem.  It's a 24" square, 2+" thick piece of MDF veneered over.  It's held up fine for about 5 years.  I'll sink it ~ 1/4" below the table top, and put a 1/4" glass insert on top. The board will be held up by some separate structure that will allow me to level it, and transitioned with little pieces of moulding:  it won't move and will accomodate all kinds of frame movement.

I don't think I'm alone in seriously misunderstanding your OP. I thought you said that you were not going to use veneer. If the quoted statement above is correct, then you don't have a serious problem. I would make the frame members somewhat less than 7", but other than that, if the center is going to float, you are good to go. Use what ever corner joints you like. If it helps, there are tables you can search that provide the amount of movement that can be expected by species. So, you can find the species for your frame that will have the least movement.