Plywood cut out/frameing for lighter weight?

[Bigblock352]

So I am in the this is really going to happen, start making drawings, ask everyone until no one wants to talk to me anymore phase.

What issues will I find with this or is this completely fine. I was thinking of using 3/4 and cutting out sections to save weight and then frame with pine or whatever for strength in the needed areas like the door frame.
The pic... Everything in Orangey Red is plywood. the zigzag areas are cut out. For reference the smaller grid squares are 2 inches, make every 3 larger squares 1 foot.

[Shadow Catcher]

You are building an airplane not a tank
Ours has 1 X 1.5 X .060 aluminum with 1/8" Filon outer skin and 1/8" luan interior and I can stand on it, so Yes you can ditch a lot of wood.

[Bigblock352]

Thanks. I keep seeing builds where people are using a full sheet of plywood and frame on top of that. I didn't think that much support would be needed, but I know enough to know I don't know. So I ask.
Thanks again.

[aggie79]

I used the method you suggested but without the additional framing. It is more than strong enough.

This is a picture of my "shell" completed minus the outside 1/8" plywood skin.

[Bigblock352]

Awesome! Glad to know and see its been done this way. I will move on with my plans then.

[grant whipp]

Hey Bigblock!

I'm one of the pioneers and huge advocates of building like this ... some folks call it "cookie cutter" ... ...! Over the years I have found that starting with a core of 1/2" plywood (cut out as needed) with a 1/8" or 1/4" interior paneling and a 1/4" exterior sheathing is way more than strong enough! I fill the voids with foamboard insulation to get a little bit of extra R-value in the walls. It's not as light as stick-framing, but it is stronger, and way lighter than solid plywood walls ... and way easier than cutting all those little sticks of wood ... ...! Lots of folks, here, have used this method, and they (as well as me) are more than happy to advise & consult.

Good luck, and as always ...

CHEERS!

[IslandStorm62]

Gentlemen,
Can you you tell me how this wall was secured to the floor?

I was thinking that the outside skin "1/4" would touch the trailer frame. The 3/4" cutout frame and the interior 1/8" skin would rest on the floor. This is causing my brother and I to consider how the wall will be secured to the floor?

[bobhenry]

Here is enough to keep you entertained for an hour or so..........

viewtopic.php?f=21&t=19442&hilit=wall+to+floor

[Oldragbaggers]

I too used this method with no additional framing. Interior and exterior skins are only 1/8" marine grade okoume ply. The exterior is covered with fiberglass. As everyone else said....plenty strong!!!



With one side skinned



And the insulation in it.

[RogHodge]

If light weight is the goal there are even easier ways. The whole foam thing could be considered. But something that you may consider is to use the"interior" skin and glue lightweight framing to that. It is incredibly easy, then you glue the outer skin to the framing ribs. There would be a LOT less waste.
You can see a partial example in my door frame. I used my patented gravity clamps (bricks) for mid-spam clamping. Other fasteners such as nails are there to hold stuff together until the glue sets, therefore not really necessary.

And for what it's worth, you are at a fun stage and with a very gracious group.

[IslandStorm62]

Build Update -
Floor board is about 75% completed. I went with a 1/2" base, 1x2 frames, insulation and 1/4" floor. The base (undercarriage) will be protected with the Water Proof Self Adhesive Flashing (it can be found in one of the threads). We will be closing up the floor and treating the undercarriage this morning and then bolting it on. Updated pics in the gallery.

Moving on...

I am planning on using the cutout method. However, we decided on a 1/2" Birch cutout sandwiched between a 1/8" internal skin and a 1/2" Birch exterior skin. This may be overkill, but I did not feel comfortable with the external skin being 1/4".

The external skin (1/2" Birch) will rest on the trailer (1/2" ledge) and screwed into the floor board framing which are 1x2s. The cutout (1/2" Birch) and the internal skin will rest on the floorboard.

Now my question - What method would be best when installing the spars for the roof?

1 - Have the spars resting on the cutout and butted up against the external skin; this means the cutout would be 1" smaller than the external skin, creating a ledge for the spars to rest on.

or

2 - Have the spars butted right up against the internal skin. This means that the external skin, cutout and internal skin are all have the same height. This means the spars are kept in place with screws and glue, no supporting ledge.

I am leaning towards #1, but have not made my final decision, would like consider other members input, comments or advice. Thanks.

[ajliquidation]

I too am getting ready for my first build and have wondered this same question many times, please help and thanks! @dam

[tony.latham]

I went with 1/4" skins in and out and 3/4" pine for framing inside. This is before the interior was bonded:


With the exception of the doorways, the vertical pine ends up routed and holds my bulkheads in place. The rear horizontal pine piece is to support the hatch counter top and interior fist shelf (a single piece of 1/2" birch ply). My fenders are welded to the frame, so I have no blocking for them in the walls.

Here's a wall ready to attach to the floor, you can see the mortises routed in for the bulkheads:


You can see the shelf cut in for the ceiling/roof ala Steve Fredrick's Build Manual. That method rocks in my humble opinion. You can lay your ceiling on the shelf,glue and staple it down, and then attach the spars on top of it.

In hindsight, I think 1/4" is a bit of overkill, at least on the interior (but it did give me a bit more beef to join the plywood for 10' sheets). When it's all bonded up, exterior, interior framing/foam, and interior, it's stiff and strong. Bulkheads and spars glued in, it's a lightweight beast of a box.

Gawd! I do miss building a bit!

Tony

[tony.latham]

By the way; when GRANT speaks, listen. Let his advice seep like a tea bag. Squeeze the bag between your fingers. Let it's aroma permeate your senses. The builders in Tibet that are monks, believe he's the Dalai Lama of Teardrops. They've got their own forum over at http://www.TibetenTeardropBuildingMonks.org Don't expect to be accepted into their forum without burning a lot of incense. Not the cheap sticks you get at Walmart that smells like somebody threw a plastic fork in your cooking fire.

I bought my hinge from him and I'm thinking he blessed it.

Tony

p.s. Some of that is the truth. Some of it may be my imagination. It's cold, snowy, and dark as old motor oil up here in Idaho, so cut me some slack! Maybe I outta fire up the shop heater and finish that DIY router lift I've been working on...

[Glenn Butcher]

Gee, I clicked the link...