Joining Two Plywood Semi-Circles (temporary tabletop)?

A friend has a small circular table with a glass top. It now seats about five people. She wants it to seat perhaps ten people and is considering getting a sheet of 3/4 inch plywood and cutting out two semi-circular pieces which, when joined together will have a diameter of 68u inches. When she needs to seat ten people she will place these two semi-circular pieces together on top of the table. What she is wondering about is how to join the two pieces whkile they are in use. She doesn't want anything protruding underneath, otherwise I would have suggested a piano hinge.
Any ideas?
Thanks.
John
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I'm thinking about a catch on either end of the semicircle that would draw the two sides together. Here's an example from Rockler. http://www.rockler.com/ecom7/product_details.cfm?&offerings_idw7 I think it's going to be pretty hard to get something that doesn't protrude. Perhaps it will be enough if it doesn't protrude against the table.
todd
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I'd make it either tongue and groove at the mating sides or biscuits glued into one side only. Then I'd put some sort of clips on either the ends or on the ends on the underside. They would not have to be on the glass top that way. Even a hook and eye could hold them in place but I'm sure there is some better hardware if you look around.
Alternatively, you could cut mortises near the end, insert a square pieced of wood and peg it from the top to be sure it is secure. Ed
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John wrote:

I think I'd still use a piano hinge on the underside of the temporary top. I'd cut a rebate along the abutting edges before installing it so it didn't protrude.
-- Jack Novak Buffalo, NY - USA (Remove "SPAM" from email address to reply)
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Sat, May 29, 2004, 11:23am snipped-for-privacy@adelphia.net (Nova) says: I think I'd still use a piano hinge on the underside of the temporary top. I'd cut a rebate along the abutting edges before installing it so it didn't protrude.
Nah. Hinge on top. LMAO
JOAT If you're offered free wood, take it, period; figure out what to use it for later. - JOAT
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You just *think* you're kidding.
A recessed, flush, hinge, such as Woodworker's Hardware sewing machine hinge (SYH 116 P) or, even better, Whitechapel Ltd's 'counter' hinge (244H36), is *ideal* for this kind of application.
It has the advantage that you can take the thing out, lay it on the table, _still_folded_in_half_, and just 'unfold' it into place.
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Mon, May 31, 2004, 6:08am (EDT+4) snipped-for-privacy@host122.r-bonomi.com (RobertBonomi) says: You just *think* you're kidding. <snip>
Nope, I flatout know I wasn't.
It has the advantage that you can take the thing out, lay it on the table, _still_folded_in_half_, and just 'unfold' it into place.
That's maybe the funniest part, noybody thinking about that.
Any woman I've ever heard of would put some kind of tablecloth over the top anyway, so wouldn't need to get too fancy, because nobody could see it anyway.
I was waiting for this one too, but nobody came up it. Just cut an interlock in each piece, about like a gigsaw puzzle, then wouldn't need any hardware at all. The two individual pieces would be lighter, and easier, to handle too. Of course, if you got some clod who leaned their elbows on the table, that might tend to pop it up at the joint. But, that's easy to fix; you either tell everybody no elbows on the table, put something heavy on the joint, or start hanging out with a better class of people. LOL.
Actually, if I was going to do something as gimmicky as a top like that sounds, I'd probably do it different. Well, first off, I'd get a bigger table probably, or make one. Or, a chunk of plywood over a couple of sawhorses, whatever. Because, this sound' prerry temporary to me. Best would probably be a table, with folding legs.
But, if something like this was really felt necessary (my personal thought is, that storing a top like that day-to-day, taking up space, would be more of a PITA then it's worth), it would need something to prevent it from being bumped out of place on the top. Because you're bound to have someone bump it. (That's another concern, small table, big heavy top, not real stable.) So, a plwood ring just big enough to fit over the present top. I would think about 6" rim, minimum, better a bit more. Then the two piece top. T-nuts in the ring, and screws thru the top, which would only take a minute to fasten. Actually, I would have the ring, then a piece of plywood just going to the outer edge of that, and fastened, then the T-nuts in that. Slip that over the original top, then set one piece of big top on, and fasten down. Much easier than trying to hold the ring in place, and fasten a piece of top to it. A hand waves from the audience, and a voice wails, "But, how do I keep track of the screws, so they don't get lost, when the top isn't being used?". Keep track of the screws? No. You screw them back in the T-nuts, so they don't get lost. And, I would use at least 3 for each side, so even if one or two did get lost, you could still hold the tops in place.
Actually, I would think the ring on the bottom, but cut and fastened to each top piece, then a hing on top, would probably be the second best bet all around. Best bet would be a totally dtifferent table, as long as you're having to store something anyway. Now, if you had a big top that was kept on day-to-day, and only taken off for a smaller top on special occassions, that'd be different.
Rube Goldberg is a hero to me, and it's always fun to emulate him. But, it never fails to fascinate me, how people cam complicate simple things. Anything that will be used time after time, is better left basic.
Hmm, now that I think about it, just using rubber cement to hold the pieces in place would probably work too. That's pretty basic. LMAO
I say make it, then an update posted, after it's been used a time or two. My thought is, the owner won't be a cheerful person in a tent.
JOAT If you're offered free wood, take it, period; figure out what to use it for later. - JOAT
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Tite Joints http://www.rockler.com/findit.cfm?page49&sid 998
ModEez http://www.mod-eez.com /
Southco http://www.southcoipsg.com/prd/lst_main.listscreen?NodeID !37&Criteria=&RecCount=6&Lang_ID=0&StartingRow=0
And there are others.
UA100
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Thanks for all the good suggestions. I was leaning towards the Adapt-N-Lock until I saw the suggestion about rebating the two pieces where a Piano hinge could then be installed. Now if I can only figure out how to rebate the plywood.
My thanks to all. There are a lot of genius's out there!
John
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John wrote:

John...
How about joining the two halves with a pair of hourglass shaped connectors? It's the easiest solution I could think of - and provides interest if the table is used without a cover. (Sketch on ABPW)
--
Morris Dovey
DeSoto, Iowa USA
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