Possible Honeycomb wall weight saving???

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Possible Honeycomb wall weight saving???

Postby R. W. Alexander » Tue Jun 08, 2010 2:17 pm

I have finally gotten a design for a Tear Drop that we like. But I want to keep the weight down as much as possible. So I am trying out this design idea. I am going to remove part of the 1/2" plywood and make a honeycomb
type of pattern to reduce some of the weight.
This first image is of a 3" x 52" piece of 1/2" plywood, drawn up in my CADCAM program.

Image


I cut 2 identical pieces one was routed and one was not, and then did a break test on them by putting on some weights.

Image


The routed piece failed at 45 lbs. while the one that was not routed went to 60 lbs before cracking.

What I am trying t achieve is a 40% or more weight reduction in the walls. Here is a image of one possible way. I will not be routing anywhere there will be frame members or connections to other areas of the trailer.

Image

Any ideas would be appreciated.
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Postby rainjer » Tue Jun 08, 2010 3:36 pm

Image

Ok, a couple questions.

How thick are the floor in the pockets where you routed?

Are you going to skin the outside with aluminum?

What are you going to use on the inside to cover the honeycomb?

Are you gong to fill the honeycomb voids? If so, with what?

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Postby mikeschn » Tue Jun 08, 2010 3:38 pm

I think it's a good idea, albeit a lot of work.

If you are skinning it with plywood, inside and out, you don't need all that honeycomb stuff in there. Just a few structural members, and some EPS.

like this...

Image

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Postby R. W. Alexander » Tue Jun 08, 2010 4:15 pm

rainjer wrote:Image

Ok, a couple questions.

How thick are the floor in the pockets where you routed?

3/8"

Are you going to skin the outside with aluminum?

Yes

What are you going to use on the inside to cover the honeycomb?

3/4" blue board/foam sheets

Are you gong to fill the honeycomb voids? If so, with what?

blue board, but I will need to figure that one some more.


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Postby planovet » Tue Jun 08, 2010 5:15 pm

mikeschn wrote:I think it's a good idea, albeit a lot of work.


I agree. Too much work for the weight savings. There are easier ways to save weight. Neat idea though.
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Postby rainjer » Tue Jun 08, 2010 6:23 pm

Based on you answers I would bet if you went a 1" X 2" frame and did a sandwich of .040" aluminum + 1/8" plywood (or 1/4") +frame with foam in the voids + 1/8 plywood you would end up with a lighter construction, just as strong and a lot less work.


You could also CNC you frame out of 3/4" plywood ans make the frame in 1 piece.

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Postby asianflava » Tue Jun 08, 2010 7:18 pm

rainjer wrote:Based on you answers I would bet if you went a 1" X 2" frame and did a sandwich of .040" aluminum + 1/8" plywood (or 1/4") +frame with foam in the voids + 1/8 plywood you would end up with a lighter construction, just as strong and a lot less work.


You could also CNC you frame out of 3/4" plywood ans make the frame in 1 piece.

Jeremy


Yep, that's how I built mine, 1X2s with 1/8in luan on both sides, skinned the outside with .040 Aluminum. My cabinetry and shelving is built from the same, except they are 1/8in blatic birch.

You could CNC the 1X2 center frame section, but 3/4in ply isn't 3/4in. The rigid insulation is 3/4in which would make your framing too short to make contact both faces.
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Postby R. W. Alexander » Tue Jun 08, 2010 9:34 pm

Thanks for the help with my wall plan. :? I will study further with the 1/8" luan ply./1"x2"/ 1/8" luan wall. I do have a question about the orientation of the 1"x2"s. Does it make a stronger wall the side of the stud is placed on the plywood?
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Postby Ageless » Tue Jun 08, 2010 10:01 pm

The strength of a honeycomb panel is in the skins. If you only apply a plywood skin on one side; it will still bend; it must have ply on both sides for optimum strength. I would use the 1/8" on both sides and float the aluminum.

Another method would be to use the 1x2 only on the external framing and door framing; fill the remaining area with foam and then bond it all together.
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Vacuum bagging and composite panels

Postby eamarquardt » Tue Jun 08, 2010 11:05 pm

See this string about ply/foam/ply sandwich made by vacuum bagging.

http://tnttt.com/viewto ... sc&start=0

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Vaccume baging

Postby R. W. Alexander » Wed Jun 09, 2010 9:11 am

I think you are right on about the vacuum bagging the Foam core/Luan ply.
I have a vacuum set up here in my shop that I use to hold down parts when cutting on the C.N.C router. I will drawing out my walls, and top with this type on construction. It should be possible to get close to the1.00 to .75 lbs. per square foot weight, that the foam core manufactured panels are.
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Postby aggie79 » Fri Jun 25, 2010 6:38 pm

I don't know what the capabilities of your CNC is, but if it can handle 4' x 10' sheet goods (or whatever size profile you're using), I'd be tempted to use 3/4" plywood "framing" instead of stick framing.

I did it the manual way with a template, jig saw and router. Here is a picture of my framing with the interior wood applied:

Image

(By the way, I left about 3" minimum width of plywood for framing. Half that width would still be plenty strong enough.)

Cut the framing, apply the skin, and you're done.
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Postby Shadow Catcher » Fri Jun 25, 2010 8:58 pm

I was just sorting through radiographs (industrial X-Ray) that were left by my father in-law. He was in aerospace through most of his nondestructive testing career and I learned radiography from him. Included in this were radiographs from Gemini and Apollo space craft. I have a couple of radiographs I took of welds on the space shuttle main engine cooling coils. Included were radiographs of wing section honeycomb with some internal failures during construction 40+ years ago. You have an inner and outer skin and paper thin honeycomb.

Folks when you build it like a battle ship you are more likely to fail, not less, because it will be more likely to try and shake itself apart.

Construction is a synergy with inner and outer skin doing most of the work. The skin on the Mega-Mini is Filon outer skin .12" (3/25ths) 1x1.5" aluminum tube that is .040 (1/25th) of an inch thick. there are a couple of sections where .060 (3/50ths) tubing is used. The trailer is strong enough to stand on.

So lighten up! :thumbsup:
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Postby katbut » Sun Sep 05, 2010 5:05 am

mikeschn wrote:I think it's a good idea, albeit a lot of work.

If you are skinning it with plywood, inside and out, you don't need all that honeycomb stuff in there. Just a few structural members, and some EPS.

like this...

Image

Mike...


Mike, when building the frame, do you build the frame first and lay it on the panels or build the frame on the panels as you go, and are you using biscuits or just gluing the frame pieces to the panels?? Thanx.
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Postby katbut » Sun Sep 05, 2010 5:07 am

mikeschn wrote:I think it's a good idea, albeit a lot of work.

If you are skinning it with plywood, inside and out, you don't need all that honeycomb stuff in there. Just a few structural members, and some EPS.

like this...

Image

Mike...


Mike, when building the frame, do you build the frame first and lay it on the panels or build the frame on the panels as you go, and are you using biscuits or just gluing the frame pieces to the panels?? Thanx.
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