Thread: Will 38mm plywood bow as a dining table?

If it was solid 38mm it should be fine, but 19mm with a built up edge might not stay flat.
It also depends on what type of ply you use, the more expensive grades (interior or marine) tend to be more stable.

Originally Posted by Gingerbread Man

I plan to make a plywood table top. I was to use 19mm ply cut to 1500x900 for the top. Then to rip the rest of the sheet up to run supports underneath and around the edge so that it looks like a 38mm table from the edge.

I have two sets of sawhorse brackets to make the legs. The idea being that the legs fold together and can be stored, and the table top can slide behind a sofa or similar.

Will a 38mm table (2x19mm sheets glued and screwed) bow in no time at all? I ideally wanted to keep the structure as thin and as light as possible so didn't want to build a frame as such.

But if it'll bow easily, I best rethink my design.

Make sure the 19 mm sheet you purchase is FLAT, when you get home store it on edge so air circulates on both sides. Make your table with built up edges,
what ever you treat the top with do the bottom at the same time, also the same amount of coats of what you use. It should stay flat. NF.

Originally Posted by Gingerbread Man

I plan to make a plywood table top. I was to use 19mm ply cut to 1500x900 for the top. Then to rip the rest of the sheet up to run supports underneath and around the edge so that it looks like a 38mm table from the edge.

I have two sets of sawhorse brackets to make the legs. The idea being that the legs fold together and can be stored, and the table top can slide behind a sofa or similar.

Will a 38mm table (2x19mm sheets glued and screwed) bow in no time at all? I ideally wanted to keep the structure as thin and as light as possible so didn't want to build a frame as such.

But if it'll bow easily, I best rethink my design.

The strips of ply along the edge won't do much to prevent warping. You will need solid timber to achieve this.

To guarantee flatness, you need to insert at least a single cross beam under the top along the longest dimension. I've used 35 x 35mm tassie oak for this in the past and it works a treat.

I've attached a photo of a table I made recently using this method with 24mm AA ply - to date it has been continuously used and it is still flat. Without the beam the 24mm ply did flex under its own weight.

The support struct it sits about 30cm from the back - the tabletop here is 1600mm wide by 800mm deep. I also painted the beam the same colour as the legs, to make the whole thing a bit more integrated.

Hope this helps,

Steven.


whole_table_4.jpgtable_underneath.jpg

Thanks for the advice guys. I could add a 4th element to the table (legs x2 and top) as a removal brace bar. A straight bit of timber should be able to find a home.
There's no room for it to permanently be assembled, so that's the brief for a collapsible/ dismantable table.

If the brace bar braced between the two horizontals of the saw horse legs, how would be best to create this removable joint? I'm picturing a joint not to dissimilar to a dovetail joint where one end of the middle brace would interact with the horizontal of the legs. Not sure how I would create this other than a saw and careful measuring though.

Ideally the assembly will require no tools.

Originally Posted by Gingerbread Man

I plan to make a plywood table top. I was to use 19mm ply cut to 1500x900 for the top. Then to rip the rest of the sheet up to run supports underneath and around the edge so that it looks like a 38mm table from the edge.

I have two sets of sawhorse brackets to make the legs. The idea being that the legs fold together and can be stored, and the table top can slide behind a sofa or similar.

Will a 38mm table (2x19mm sheets glued and screwed) bow in no time at all? I ideally wanted to keep the structure as thin and as light as possible so didn't want to build a frame as such.

But if it'll bow easily, I best rethink my design.

if you can rip consistent width strips, build yourself a torsion box top with solid wood edges.
6mm ply would do, but might sound too hollow.
a stapler is real handy when it comes to assembling the frame. and a brad nailer for the top and bottom.

also a torsion box will be much lighter than a 19mm ply top

Originally Posted by ian

if you can rip consistent width strips, build yourself a torsion box top with solid wood edges.
6mm ply would do, but might sound too hollow.
a stapler is real handy when it comes to assembling the frame. and a brad nailer for the top and bottom.

also a torsion box will be much lighter than a 19mm ply top

A torsion box was an idea. Setting the frame slightly in from the extremities, and then cutting plywood down to create the plywood effect down the side. 6mm ply would sound hollow you are correct. I don't want it heavy heavy, but I think if it was too light it might be a bit flimsy, pivot when lent on?

Originally Posted by Gingerbread Man

A torsion box was an idea. Setting the frame slightly in from the extremities, and then cutting plywood down to create the plywood effect down the side. 6mm ply would sound hollow you are correct. I don't want it heavy heavy, but I think if it was too light it might be a bit flimsy, pivot when lent on?

probably not

when I was a kid, dad made a base board for my train set. From memory it was 1/8 or maybe 3/16 ply nailed to a square grid made out of 1" Tassie oak. Effectively he build a torsion box with a top skin only. The train set base board rigid enough to allow a 14 year old kid to walk on it.
I don't think a 38mm deep torsion box skinned in 5mm ply would be too flimsy to use as a table top. At a minimun it will be no more flimsy than two layers of 18mm ply that are not attached to the supports. The key is how the top when in use is attached to the supports.

If you must go the torsion box route, then thats pretty much the size of the largest-size hollow-core door available - cut to length. TB already made.