Any MechEs handy?

[groza528]

I have decided that I would like to try my hand at building some of my own furniture.

The kitchen table I want to build will have a spring-loaded leaf. The basic gist is the table will be roughly 4'x5.5' with a 2'x4' leaf in the middle. What I'd like to do if have the two halves of the table slide out on basic drawer tracks, and have the leaf held down by push latches and spring into place when you press down to release.

The tabletop itself I'm planning to make from 3/4" plywood with white panelboard (maybe 1/4"? estimating) laminated to it. The big questions I have are:
1. What type and strength of compression spring do I need to use here? Are arched strip metal springs a better choice than coil? How strong does it need to be in order for a normal person to press down enough to latch (~1.5" displacement) but to still hold normal dinner table weight? The weight of the leaf itself is ~20lb.
2. Do I need to worry about the balance or strength of the table if the legs don't translate with the tabletop? Will the drawer mechanism hold the 1' cantilever and normal dinnertable weight?
3. Will the force of the springs cause the depressed leaf to buckle or distort?
4. Should I be worried about the tabletop itself not having enough mechanical support due to the necessity to leave clearance for the leaf?
5. Are there any other factors I'm not considering that could be obvious design flaws?

If this goes well I have a coffee table planned also, though that probably won't have *as much* room for mechanical failure.

[The Potter]

Coil springs work pretty well when there is space for them.

...

So you slide open the normal table and see a middle panel. Somehow you press it to make it rise up an inch. My feeling-- you are going to have a very difficult time making it fit let alone fuss with spring loaded mechanisms.

So how about this instead-- a table that opens up along a track and the outside parts fall an inch to make a larger level table. That way you only have to worry about some moving supports and spacers.

[groza528]

Hmm... that definitely seems like it would have more mechanical strength as a table and be easier to fit.
How would you go about designing the mechanism where it slides out and then drops? Or rather, I guess that's the easy part, how do you make it so it's not too difficult to lift and replace?

[Buzzsaw]

Am trying to get a visual of exactly what you're doing and what you'd like to do. Am thinking though from your description you're already beyond my skill level.

[Nsof]

Trying to find a design I had in mind I found this. http://www.finewoodworking.com/item/45716/extension-dining-table
Unlike this one, in all extension tables i have seen and used the legs were static and only the table top moved.

I have seen some form of drawer type slides but mostly these:
http://www.tablelegs.com/Parts/TableSlides.aspx
http://www.rockler.com/product.cfm?page=765

Also the extension in the designs I have seen is usually placed/"hidden" in a compartment under the table right below where it would be placed but perpendicular in direction).

None of these designs requires vertical alignment of the tabletop pieces

IANAME
_________________
Will sell this place for beer

[The Potter]

Quite simply, I have never liked any table that could be two different sizes. It seems like a good idea but losing the rigidity never makes it worthwhile.

If the table is against a wall normally, a traditional drop-leaf design would be better.