Skeletonizing: How much is too much?

[Kampereen]

My third motorcycle tent trailer build is beginning to take shape and I'd like to subtract some weight. I've read some of the threads here on skeletonizing plywood which I plan to try. I don't want to be greedy -- I'm hoping for a 25% to 33% weight reduction on the vertical panels. I don't plan to cut all the way through, but rather route out enough to leave 2 ply for the exterior skin. In this pic, the triangles on the exterior are for illustration, I will be removing inside material. I'm wondering...

Has there been any discussion in the forum on the *amount* of material that can be removed?
Are there preferred shapes for creating voids?
Are there any critical "do's" or "don'ts"?
Can this be done to a lesser extent on horizontal surfaces? I'm not taking anything out of the cargo box base where the half axles are mounted. However, the panel in the upper left is the cargo box top/upper bed panel. That panel seems like it might be a candidate. It will only bear about 100 lbs, on average (half body weight) and it will have support underneath

I am excited to try this technique. This is really going to help me cut a lot of weight. Appreciate any feedback, tips, thoughts.

Kampereen 3 Prototype.jpg (62.5 KiB) Viewed 1202 times

[tony.latham]

I don't know of a definitive formula. Generally, I think most builders leave too much wood. I also think Tim Curry, aka Noiseoil nailed it with his build. You can find a photo of his skeleton somewhere in his build log:

http://www.tnttt.com/viewtopic.php?f=50&t=60248&start=15

He's a retired roof truss designer so knows stuff the rest of us peons don't.

Tony

[noseoil]

If you "skeletonize" the plywood, it needs to be skinned on at least one side. That being said, triangles are probably better than rectangles, but it's a moot point if both sides are skinned with 1/8" Baltic birch or the equivalent in an underlayment grade of plywood (Lowes or Home Delay). You need to leave enough material behind, but remember that any "hard points" need to be in place for fastenings, lights, cargo hooks, etc. Here's our 5x9 Benroy side whittled out & set in place to show what was done for structural strength.

[Kampereen]

I don't know of a definitive formula. Generally, I think most builders leave too much wood. I also think Tim Curry, aka Noiseoil nailed it with his build. You can find a photo of his skeleton somewhere in his build log:
http://www.tnttt.com/viewtopic.php?f=50&t=60248&start=15

Thanks Tony, that build is a useful reference. Appreciate it.

[Kampereen]

If you "skeletonize" the plywood, it needs to be skinned on at least one side.

Thanks Tim, I will be leaving 2 ply to the outside, so I'll basically be scooping out material on the inside. Those pics from your build are very helpful. It's really surprising how much material can be removed.

[swoody126]

somewhere in the back of my feeble remembery i'm hearing a little birdie saying NO SHARP CORNERS

sharp corners are where cracks emanate frum

drilling a decent sized hole at the end of each straight cut is what i think i'm rememberizing

if you cut your straight runs w/ a circular saw stop cutting away frum the corners and finish them out w/ a saber saw

i do like the swiss cheezy looking framing filled w/ foam

sw

[eLink]

somewhere in the back of my feeble remembery i'm hearing a little birdie saying NO SHARP CORNERS
sw

I think the rounded corners may provide some stability during construction. But, it seems to me, once the skins are on the rounded corners serve no purpose.

[saltydawg]

What curves do is spread the load over a larger area to prevent cracks.

As for how much you need to leave, the answer is none. My build is foam core panels with fiberglass skins, I only reason i did anything in panel because of the pop top. I can stand on my trailer panels with no issue, as long as you get good glue bonds between the foam and skins.

The build I am doing next for a friend will be foam cored panels with 1/2 mdo ply on the out side and luan on the inside, no framing except around doors/windows ( I may not even do that ) and where needed to join panels.

[Kampereen]

My first attempts at skeletonizing turned out okay. Of course the first one took me an afternoon, the second, an hour, the third, about twenty minutes. I have had prettier results with a router, but this was my first experience with removing this much material. I'll get better results next time. After reassembling the box I also found that I should have more carefully considered component placement, e.g. rear lights, mounting points for tent poles, etc. There are no dealbreakers in what I've done but for the next build I will sketch out the components and design the voids around those.

I took out roughly 30% of the weight from the three panels that make up the fixed sides of the lower box. That gave me a savings of approximately 10 lbs. That doesn't sound like much, but cutting 10 lbs from an estimated finished weight of 250 is a really nice savings. If nothing else, it adds 10 lbs to the budget I can use elsewhere if needed. It was messy, and I made a couple of mistakes I'll have to fix, but the panels are still strong enough to suit their purpose. I would definitely do it again.

IMG_1769.jpg (327.13 KiB) Viewed 985 times

[QueticoBill]

What curves do is spread the load over a larger area to prevent cracks.

As for how much you need to leave, the answer is none. My build is foam core panels with fiberglass skins, I only reason i did anything in panel because of the pop top. I can stand on my trailer panels with no issue, as long as you get good glue bonds between the foam and skins.

The build I am doing next for a friend will be foam cored panels with 1/2 mdo ply on the out side and luan on the inside, no framing except around doors/windows ( I may not even do that ) and where needed to join panels.

Excellent. I'm planning on going this way - 1" xps core and 1/4" ply both sides of walls, 2" xps core and 1/8" on both sides roof/ends.

[noseoil]

"Next time" use a template & start in the center & work out to the edges, that way the router base is always supported & can't drop on you. Leaving the thin amount of wood on one side helps with support of the panel to distribute the loads through that skin & back into the rest of the structure. 10# saved is 10# spent elsewhere for the good!

[tony.latham]

There are no dealbreakers in what I've done but for the next build I will sketch out the components and design the voids around those.

Once you have one skin on, you can glue back hardpoints for whatever you need to support.

Tony