MDF or ply - best for table-tennis table top?

It's been suggested that a (small) ping-pong table would be a good idea for the kids; due to space constraints the proposal is to make a table-top version which will sit on top of our (very sturdy) 6'x3' dining table; the add-on will actually be 1880 x 1046 mm, ie slightly overlap the underlying dining table in the same proportions as a regulation table-tennis table.
The idea is to make this in two halves (ie cut along the net) which can be removed easily to recreate a dining room at will; I was going to attach lipping underneath around the edge to bear against the edge of the dining table, to hold it in place. Top will be in 12mm thick board I think (compromise between weight/durability/ball bounceability).
So, the question: what sort of board would I be best using? In real money, we're talking two sheets approx 4'x3'. I'm thinking ply or MDF: which would be best in terms of resistance to warping, given that it will be used in a CH house and probably stored vertically in a garage when not in use?
Thanks David
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Lobster wrote:

I'd go with ply, but I'd personally want to use 3/4". The reason I'd choose ply is that biggish bits of mdf have a tendency to sag when stored leaning against a wall, e.g. in the garage.
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On Sun, 03 Apr 2005 13:18:17 GMT, Lobster

I would use 18mm ply for this, because for the thickness it is quite a bit lighter than MDF and will not tend to warp unless you lean things against it.
I'd also suggest going to a timber merchant rather than DIY store and get a better grade than the rough stuff that DIY places have. Quite often the rough grades have blemishes and filled holes which obviously you don't want.
In addition to the lipping to locate it on the table, I would also put some around the edges of the ply to protect it a bit.
Where does the regulation size come from? It's an odd number even in deprecated imperial units.
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.andy

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On Sun, 03 Apr 2005 13:18:17 GMT, Lobster
Birch ply - 15mm
MDF is heavy and has a tendency to sag. Although the board is cheaper, you'd have to egg-crate support in underneath at about 9" spacings. You'd probably get to 6mm by doing this, but that's starting to be risky for damage when stored vertically. MDF is probably cheapest, but a properly supported table would be twice the work.
Tropical plywoods are cheaper than birch, but the surface texture is coarser. You'd have to do a lot more surface prep to make the playing surface.
Birch ply (of good quality) is made from thinner veneers and more of them, for a given thickness. Mechanically it's a superior board, enough so to be worth paying for.
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Andy Dingley wrote:

Thanks for the replies, all.

Looks like ply then, thanks. Everyone's saying I need more than the 12mm thickness that I'd envisaged; Andy you mention achieving thinner board using egg-crate support, but why would that be needed given the fact that, in use, the entire surface will be supported from below by the dining table (1" solid timber)?
One tweak I thought of overnight, having slept on it!, would be to fit small door bolts to the lipping under the table all round, with the smaller female component attached to the bottom of the dining table - then when I put down the table-tennis top, by sliding the bolts home, it would hold it down rigidly, correcting any slight warp. Which would enable thinner board to be used?
David
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On Mon, 04 Apr 2005 09:04:28 GMT, Lobster

I'm not convinced it will always be used on the dining room table. Also I don't know how big your table is, and how wide a support it will provide.
I'd probably still eggcrate it though. I can't see a way that the table can support the top, both directly above it and cantilevered out to the sides, without some sort of intervening frame. If you do even a bit of this, you need to support the whole top on it. . If the dining table does give good support though, 12mm ply should be adequate with just an edge frame to stop the corners drooping (stops it sliding off sideways too).
Glue some rubber mousemat underneath as anti-slip strips.
--
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Lobster wrote:

I have played on both ply and hard chipboard. In many ways I preferred the chipboard. Edges do decay a bit leading to fluke shots.
Never tried MDF, but it should be OK, but dion't discount chibboard.
Pretty sure our table was 8x4 and 9x5 is the 'correct' size..
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The Natural Philosopher wrote:

Can you get a good smooth and reasonably resilient playing surface with chipboard?
David
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Lobster wrote:

A few coats of matt PU, with sanding between coats, will make just about anything smooth and resilient. Don't know if/how it will affect how the surface plays though.
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On Mon, 04 Apr 2005 09:05:55 GMT, Lobster

Probably, if you soak it with paint or varnish.
However, like MDF it's heavy for a given size.
Regarding Andy's comment about eggcrating with ply, I tend to agree.
This is quite a common method with workshop tables etc. to achieve rigidity without adding weight. Again thinking about your wanting to stand the pieces in the garage, this would be a way to reduce the risk of bending.
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.andy

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wrote:

I've got, from childhood, a quarter size snooker table that stood on the parental dining table. This is chipboard stood on little rubber grommet feet.
As long as the table was flat, it stayed flat, but did tend to sag when one of the leaves beneath it drooped.
I worry that your orignal plan might be prone to damaging the table when being slid on and off.
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