3/4 vs 2x4 Skeleton Frame

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3/4 vs 2x4 Skeleton Frame

Postby MJWBuffalo » Tue Dec 24, 2019 12:09 pm

I am committed to building with a skeleton frame but am a little confused as to the benefit of doubling up 3/4" plywood strips vs using 2x4's off the shelf for my frame. I have seen some of you do it both ways but I am completely baffled as to the benefit of the double 3/4" plywood. I need to end up at 2" thick so I'll be skinning with 1/4" plywood either way.

Is the 3/4" lighter? Stronger? Cheaper?

Otherwise it seems like a LOT more work to rip down sheets of 3/4" ply into 3.5" strips and glue it all together in order to make basically a perfectly true 2x4.

Color me confused...

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Re: 3/4 vs 2x4 Skeleton Frame

Postby tony.latham » Tue Dec 24, 2019 12:27 pm

a little confused as to the benefit of doubling up 3/4" plywood strips vs ...


Doubling up 3/4" plywood strips? I'm not sure what you are referencing.

Building a skeleton from 3/4" plywood is an easy task. No joinery, other than lengthening which is simple with a 1/4" slot cutting router bit.

Image

I gang cut them. Two at a time. :thumbsup:

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Re: 3/4 vs 2x4 Skeleton Frame

Postby KTM_Guy » Tue Dec 24, 2019 5:23 pm

Tony pointed out his way for the walls. But my question is why would you want 2” walls? I can’t see any advantage over a 3/4” or 1” wall. I went with a 1” wall but that was because I couldn’t find 3/4” rigid insulation in my area and was able to find 1” Baltic Birch.

While building keep in mind you want to build like an air plane not like a tank.

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Re: 3/4 vs 2x4 Skeleton Frame

Postby siena » Wed Dec 25, 2019 9:00 pm

tony.latham wrote:
a little confused as to the benefit of doubling up 3/4" plywood strips vs ...


Doubling up 3/4" plywood strips? I'm not sure what you are referencing.

Building a skeleton from 3/4" plywood is an easy task. No joinery, other than lengthening which is simple with a 1/4" slot cutting router bit.

Image

I gang cut them. Two at a time.

Tony
Tony for the skeleton frame, to insulate that would you just cut foam board to fit in between the skeleton? And then skin in plywood or aluminum?


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Re: 3/4 vs 2x4 Skeleton Frame

Postby tony.latham » Wed Dec 25, 2019 9:16 pm

siena wrote:
tony.latham wrote:
a little confused as to the benefit of doubling up 3/4" plywood strips vs ...


Doubling up 3/4" plywood strips? I'm not sure what you are referencing.

Building a skeleton from 3/4" plywood is an easy task. No joinery, other than lengthening which is simple with a 1/4" slot cutting router bit.

Image

I gang cut them. Two at a time.

Tony
Tony for the skeleton frame, to insulate that would you just cut foam board to fit in between the skeleton? And then skin in plywood or aluminum?


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Yes, 3/4” foam board which can be a challenge to find. Some use 1” and trim it down with a hot wire cutter.

On this last tear, I used 1/8” Baltic on the inside and 1/4” on the exterior. You might want to peruse my recent build log.

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Re: 3/4 vs 2x4 Skeleton Frame

Postby MJWBuffalo » Thu Dec 26, 2019 8:13 am

All:

Thanks for the replies. I always forget that I need to explain my project a little before questions like this as it's a little different....

I am building a standie on a 5x9 trailer that will operate as a food trailer. While the footprint is 5x9, it widens at the top by a food on each side for a total of 11'. Because of all this, I will have a large awning window (around 60"w x 40"h) on one side with pneumatic lift supports. I am concerned that the added stress of that would necessitate the need for a beefier frame.

After reading your replies and doing some more searching, I think I'll stick with the thicker walls just to be safe but I like the idea of doubling up the 3/4" ply instead of 2x4's. I can cut out the middle of the panels like you've shown to cut down on the weight/add the insulation. Since I'll be using 3 sheets of ply per side, I can overlap the seams and glue/screw to make it a stronger more cohesive wall.

I'll cover the outside with 1/4" ply before aluminum and inside will have FRP to make it easy to wipe up.

Thanks again!

Matt
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Re: 3/4 vs 2x4 Skeleton Frame

Postby noseoil » Thu Jan 02, 2020 9:08 am

You really don't need the extra beef of 1 1/2" material for walls. 3/4" plywood with 1/8" skins is plenty of strength. The 3/4" skeleton frame isn't that strong by itself, but once the 1/8" material is added to the inside & glued in place, it's pretty much bullet-proof as far as structural strength. Adding 1 1/2" insulation may be necessary, in which case 2x4 would be ok, but I would use 1x2's for the framing to save weight & cheapen the build cost. 3/4" is plenty strong with skeleton wall construction.

I'm with Tony on this one!

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Re: 3/4 vs 2x4 Skeleton Frame

Postby MJWBuffalo » Thu Jan 02, 2020 11:51 am

Thank you for the reply!

I'm going to take the advice of all your wise tnttt vets and build it with a single layer of 3/4" plywood. I'll cut out the interior spaces and fill with foam to provide some insulation. Then I'll glue RFP on the inside and glue/screw 1/4" plywood on the outside before floating the aluminum skin.

Thanks again for the input. All of your expertise probably helped me shave another 150-200 lbs from the trailer!

If anyone else has input, I'd love to hear it

Matt
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Re: 3/4 vs 2x4 Skeleton Frame

Postby saywhatthat » Thu Jan 02, 2020 6:53 pm

make sure that you seal around foam .Any gaps will let cold/hot air pass
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Re: 3/4 vs 2x4 Skeleton Frame

Postby MJWBuffalo » Thu Feb 06, 2020 4:24 pm

I have seen lots of pics of everyone's skeleton'ized frames but the width of the supports seems to vary. Is there a minimum width each "bone" of the skeleton should be to provide enough structural support? :thinking:

It's a delicate balance between loading it up with insulation and providing enough support so the whole thing doesn't get wobbly :frightened:

Thanks everyone!

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Re: 3/4 vs 2x4 Skeleton Frame

Postby tony.latham » Thu Feb 06, 2020 4:51 pm

Is there a minimum width each "bone"...


I wish I knew that answer, but I have always thought that Tim's skeleton, aka noseoil, is all that is needed. He made a career of designing roof trusses so that should speak for itself.

This may explain my skeleton a bit since some of it is chunky:

Image

The reason for the 4" along the outside edge in the galley is because 2" of it gets cut off for the hatch ends.

I don't know who this guy is but he sure looks cool in this video.



That'll show the hatch ends.

Tony
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Re: 3/4 vs 2x4 Skeleton Frame

Postby saywhatthat » Fri Feb 07, 2020 4:45 am

will operate as a food trailer. Why would you use any wood There a reason food trucks use SS are alum. most food trailers are molded fiberglass Faster to clean . no place for bad bugs to live
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viewtopic.php?f=50&t=66751
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http://tnttt.com/viewtopic.php?f=50&t=70729
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Re: 3/4 vs 2x4 Skeleton Frame

Postby MJWBuffalo » Fri Feb 07, 2020 10:30 am

Thanks for the replies. I'll keep it beefy around the edges but it's good to know I can cut it back to 2" or so in the middle!

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