How to build a removable dining table extension?

Question

I'm looking for advice on whether my idea for a cheap, removable dining-table extension is sound, particularly around stability and how best to secure everything.

My existing dining table is 1000mm wide. I want to temporarily extend it when I have extra guests, but I don't have space to store another full-size dining table. I want the extension to match the width or the existing table which is 1m wide.

My current plan is to buy a second-hand 1200 × 600mm folding/trestle table for around $30 and use that as the supporting base.

I want the finished extension to be 1500mm long × 1000mm wide. It will connect to the end of my existing 1000mm-wide dining table and should give me room for five additional diners – two on each long side and one at the outer end.

Rather than using one large 1500 × 1000mm sheet, I want to make the top in two pieces because they'll be much easier to handle and store vertically beside my fridge.

I'm thinking of buying 17–18mm plywood or formply and having it cut into two pieces measuring 1500 × 500mm each.

The two pieces would sit side-by-side, with the join running lengthways down the middle:

1500mm
       ┌──────────────────────┐
       │                      │
500mm  │   1500 × 500 panel   │
       │                      │
       ├──────────────────────┤
       │                      │
500mm  │   1500 × 500 panel   │
       │                      │
       └──────────────────────┘
                 1000mm

The 1200 × 600mm folding table would be centred underneath. This would give the plywood top a 200mm overhang on each side and a 150mm overhang at each end.

The two plywood panels would need to be securely connected together while the table is being used, but I want to be able to separate them afterwards for easy storage.

My initial thought was removable timber battens underneath spanning the join, but I'm completely open to a better or simpler method.

I'm also happy to screw into or permanently attach brackets, blocks or other hardware to the folding table if that's the best solution. As it's only a $30 second-hand table and will be dedicated to this purpose, modifying it isn't an issue. I'm just not sure whether attaching the top to the folding table is actually necessary.

Ideally, I want the two plywood panels to lock together securely and the completed top to be unable to slide or tip, while still being quick to dismantle after use.

I could also use non-slip rubber matting between the folding table and plywood if useful.

A tablecloth will cover the entire thing, so the appearance of the plywood and centre join doesn't matter.

Does this sound like a safe and stable design for normal dining use?

I'd particularly appreciate advice on whether 17–18mm plywood/formply is the right material and thickness, whether the 200mm side overhang is reasonable, the simplest removable way to join the two plywood panels, and whether/how you would secure the completed top to the folding table to eliminate the risk of sliding or tipping.

I'm trying to keep the whole thing cheap, simple, stable and easy to dismantle and store.

EricL · Answer

Hello @Kingleviathan

Just to add to the excellent suggestions made by Jacob. I propose building sawhorses to support the table instead of getting a trestle table. The sawhorses would provide a much sturdier base and will not wobble even with heavy items on top of it. I've placed some sample sketches below to give you an idea of how they can be linked together. The tables can be joined together using a timber frame as a guide and the other side can be fixed in place using a bolt with a butterfly nut at the bottom.

If you need further assistance, please let us know.

Eric

pete_brig · Answer

@Kingleviathan

Some quick thoughts in response to Jacob's tagging:

* consider something like a piano hinge to join the 2 plywood sheets. Without looking I'm guessing there are fixings you could use to lock the 2 sheets when they're open, or use some type of quick release in conjunction with the battens you mentioned—the battens are a good idea to add rigidity.
* rather than the 2nd hand table, consider some foldable trestles for the base. They'd make the whole package more easily stored rather than just the table top. Custom built so you can ensure the extension aligns with the existing table. and there are vaious fixings that could be used to lock the trestle legs to avoid collapsing. 
* Maybe consider some sort of fixing to attach the extension to the existing table to avoid any separation/gap & further enhance stability.
* As an aside, looks like your drawing might've been created in Excel. If you've got it, PowerPoint(*) is handy to use to create plans—not as good as Visio bcos you'll have to do your own scaling in your head (e.g. 1 cm in drawing = 10 cm in the real world). I've used it to room layouts, house layouts, plans for pot plant stands

(*) No, I'm not affiliated with Micro$oft but I use what's practical & available (=cheap 😁)

Cheers, Peter

JacobZ · Answer

Hi @Kingleviathan ,

I think your idea is certainly workable, but I'd want to mechanically connect the two plywood sheets together and secure the completed top to the folding table rather than relying on non-slip matting alone.

For joining the two sheets, I'd look at installing several flat steel plate brackets across the join on the underside. Instead of screwing and unscrewing these directly into the plywood each time, you could install threaded inserts into the underside of each plywood panel. You could then bolt the flat plates across the join when assembling the table and simply remove the bolts and plates when you want to store it.

I'd use at least a few plates along the 1500mm join rather than relying on one at either end. This should help keep the two sheets aligned and stop one panel moving independently of the other. Just make sure your bolts are appropriately sized so they can't come anywhere near breaking through the top surface.

I'd use a similar principle to secure the plywood top to the folding table. Once you have the second-hand table, have a look at its frame and see where you could position some additional brackets along the edge of the table. You could permanently attach the brackets to the folding-table frame, then use threaded inserts and removable bolts to connect them to the plywood top. That way, once everything is bolted together, the folding table and two plywood panels effectively become one unit.

The 200mm overhang down each side and 150mm at the ends doesn't sound excessive to me for normal dining use, provided the folding table itself is sturdy and the plywood top is securely attached. I'd still test the assembled table carefully before use, particularly by applying downward pressure around the perimeter and corners to make sure there is no tendency for it to tip or flex excessively.

I'd probably lean towards 18mm plywood rather than going thinner. With the two panels securely joined and fixed to the supporting table, I think you could end up with a fairly simple setup that can still be dismantled into three manageable pieces when you're finished with it.

Allow me to tag some helpful members to see if they have any ideas @WoodenGregsWood, @Alicia_Woodwork, @TedBear @pete_brig.

Let me know what you think.

Jacob