3/4 vs 2x4 Skeleton Frame

Anything to do with mechanical, construction etc

Re: 3/4 vs 2x4 Skeleton Frame

Postby Absinthe » Wed Jun 03, 2020 11:51 am

tony.latham wrote:
QQ; the benefits vs a full sheet are mainly for weight and if weight is not a concern it's fine to go with a full 3/4 sheet?

If you are asking about the benefit of a sandwiched wall vs a solid one, here's my opinion:

1. The resulting structure is a torsion box that is stiffer than a single sheet of plywood with close to the same weight.

2. This method makes it easy to "stretch" plywood beyond the normal 8' length using a simple spline joint in the skeleton cut with a router bit. The exterior/interior sheathing that is glued on acts as a gusset and strengthens the joint.

3. Insulation. I purchased my first teardrop in 2004. It had solid plywood walls. On cold mornings we would always get condensation on the walls. We kept a bath towel in the cabin just to wipe them down in the morning. This would happen even with the cabin well ventilated. Condensation doesn't form on insulated walls.

4. A thicker wall allows for deep dados (or slots) to be included in the wall for bulkheads and any other cross members. This joinery makes for a much stronger cabin and is easier to assemble since these parts just slip inside the walls. Think mortise and tenon. (And yes, this is easy to do with a simple router jig.)

5. The thicker wall allows for a lip to be formed on top of the wall so that the headliner can be installed prior to the spars. This creates a perfect interior wall/ceiling joint that doesn't need to be covered by trim. (Having done this a few times, I can't even imagine having to install the headliner after the spars are installed.)

6. The thicker wall allows for a Fredricks style hatch that has a seal system that is water and dustproof.

Sandwiched walls are more labor-intensive but you end up with a stronger cabin that is insulated with a galley that doesn't leak.


Looks like I know how I am building my walls now!

My initial plan was sandwich construction (1/4, 3/4, 1/4) but without area for foam/just solid ply.

Your condensation comment has cemented that including the foam/insulation is a must!

Thanks Tony!
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Re: 3/4 vs 2x4 Skeleton Frame

Postby saywhatthat » Thu Jun 04, 2020 12:12 am

As this to be a food trailer .I ask the powers to be what do they want the inside to be . Sad to build something then have to tear apart ,even the little push carts here . have to have food grad gel-coat / S S / sealed plastic .
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