More fun with plywood

[Viva]

That's basically how cored fiberglass boat decks work (if I'm reading you correctly). They are a glued tension "sandwich" make-up of thin fiberglass skins (usually one of them is thicker, e.g. the top of the deck; and one thinner, e.g. underside of deck) bonded to a foam or balsa wood core. These end up much stronger than a cabinet door needs to be, but with wood skins instead of fiberglass, they should be lighter.

A friend's RV dinette table is thin skins, a wooden internal border frame (maybe 2 x 2?) and then foam interior. I don't think it's even really bonded, but it is thicker at around 1-1/2".

[witoke]

Originally Posted by Viva

That's basically how cored fiberglass boat decks work (if I'm reading you correctly).

A friend's RV dinette table is thin skins, a wooden internal border frame (maybe 2 x 2?) and then foam interior. I don't think it's even really bonded, but it is thicker at around 1-1/2".

Yup, that's it. And the technique is not limited to things that float: Cored materials are pretty common everywhere nowadays really. A lot of the panels in modern passenger aircraft are built the same way, as have th though they use slightly more exotic materials like aluminum and nomex sandwich, carbon fiber and so on. Hell, the British WWII Mosquito airplane was built mostly with a ply/balsa sandwich though balsa is quite heavy compared to some of the modern core materials. It was a devastatingly successful plane. Most European campers have used this technique for decades for the interior construction, weight being an issue when you can't afford to run a vehicle that gets 10 or 15 mpg. Even cheap interior house doors are cored, usually with luann skins and paper honeycomb.

You can build a very stiff and very lightweight panel and can 'tune' the end product's characteristics by choosing different core and skins. Ply and foam core makes a nice combo for light cabinetry. Glass the top for a surface you can use as a counter.

[boywonder]

Originally Posted by witoke

If you really are trying to get light sheets, you could try making the middle strips really small, just trim pieces around the edges basically, then use a foam core. That way you'll be able to use the lightest material for skins while still having stiffness and better puncture resistance.

Interesting idea.....and foam is readily available at the local lumberyard/home center.

A few practical issues with really thin perimeter strips (at least for me) are that I make the panel slightly oversized then trim to size in the table saw. Too thin to start with=start over. In the van we also need places to screw into, so that requires some additional strips especially if using 1/8" skins....and some planning ahead.

The foam is a very interesting and do-able idea that should slightly increase stiffness when glued in but I can't imagine that it would do much for puncture resistance. The foam would also provide some damping which would potentially quiet thin hollow panels. I'm also assuming gluing on my vinyl covering would also sufficiently damp panel vibration.

The local metal supply house sells honeycomb cores made from something exotic, but they are $$$.

[boywonder]

Originally Posted by larrie

What size, LxW, test panels did you make? I did not see where you said.

13 1/2" x 7 3/4".....all ended up 3/4" thick.

[dhally]

Our Itasca motorhome had some lightweight panels like that. They used pine lumber for the inner members.

I wonder how much total weight would be saved in a typical camper van? I like full 3/4" plywood because I can screw into it or drill holes wherever I want to.

[boywonder]

Originally Posted by dhally

I wonder how much total weight would be saved in a typical camper van? I like full 3/4" plywood because I can screw into it or drill holes wherever I want to.

True....with the sandwiched panel construction you need to plan for where you want screws....not always easy.

[Pntyrmvr]

Hi,

I agree with the need for planning on where to screw or drill, but one could always add a glue-in block or strip as backing if the need arose in the future.

Carbon fiber cabinets anyone?

Regards,

Gavin

[boywonder]

Originally Posted by Pntyrmvr

Hi,

I agree with the need for planning on where to screw or drill, but one could always add a glue-in block or strip as backing if the need arose in the future.

That would be tough with the method in this thread......

[Pntyrmvr]

Hi,

I meant on the inside of the cabinet. A washer or nut made of BB so to speak.

Regards,

Gavin

[boywonder]

Originally Posted by Pntyrmvr

Hi,

I meant on the inside of the cabinet. A washer or nut made of BB so to speak.

Regards,

Gavin

With 1/8" skins, it would probably crush....would probably work with 1/4" skins....