Sandwich Skeleton Questions aka Getting Meat Off the Bones.

Anything to do with mechanical, construction etc

Sandwich Skeleton Questions aka Getting Meat Off the Bones.

Postby eodmike » Sun Mar 04, 2018 9:10 am

So I'm starting the planning phase of my teardrop. I'm hoping to have it constructed for a late August early September trip. My current tow vehicle is a Nissan Altima. So weight is a concern.

I'm currently working on converting the Generic Benroy Plan into Solidworks. Long story short I'm a Controls Engineer at my place of employment and they have a need for me to understand at least basic Solidworks. So as a learning exercise they are allowing me a few hours a week to work on this on company time. Yea me.

I work for a machine builder and we have lots of fancy tools like CNCs and Waterjets. My friend happens to be the boss of those machines so I get access. I tell you all this to explain where I am.

I think I need the loaded weight of the trailer under 1,000lbs. I looked at foamies and love the idea but want the classic look of aluminum. So I'm trying to build as light as I can using sandwich walls. The decision was made based off of a desire to go light so no full plywood walls. And wanting aluminum exterior so no foamies. Plus the advantages I have of having a waterjet and cnc to use means I can build the skeleton quicker than most could do a frame.

I'm thinking .04 aluminum for the exterior skin and 1/8" luan for the interior. I think 3/4" plywood for the cabinets and skeleton. I could be talked down if people think I could go skinnier. My plan for the skeleton is to leave 3/4" of material around the entire outside and the door area then leave the same where my cabinets are. Is 3/4" enough? Can I go thinner? I plan on rounding the inside corners of my cutouts to a .5" fillet. If I downsize the cabinets to 1/2" plywood then my plan is to downsize the ribs as well while leaving the outside 3/4". Would that be ok? I will fill the cutouts with foam board. I do need to route some wiring but my hopes are to run the wires through the ceiling area and drop into a raceway between my galley and my inside cupboards.

I also will need to run some stabalizing ribs to the door frame area because obviously it can't float in space. The cabinets I'm not sure I need to run support ribs. If I do it might be stronger but my understaing is most of us are making the skeleton stronger than needed. If I don't then well less weight. I guess I need some amount of area for glue to hold the skins in place so maybe I'll need to run a few ribs for that?

Am I headed down a decent path? Any feed back? Thanks!
eodmike
Teardrop Inspector
 
Posts: 11
Joined: Tue Feb 27, 2018 5:35 pm

Re: Sandwich Skeleton Questions aka Getting Meat Off the Bon

Postby tony.latham » Sun Mar 04, 2018 11:23 am

I suspect anyone that's built a sandwiched wall has had the same thoughts.

Here's the last skeleton I built and I think it's a bit overdone but not much. (It's 10' long joined by a spline joint just forward of the door opening. The joint relies on the plywood sheathing for strength and thus the extra wood for a glueing surface.) And there's extra wood in the galley since it'll be sheathed with 8' long 1/4' plywood that's butt joined back there.

The rear of the skeleton edge is 4" since I use Fredrick's method that utilizes the outside of the wall as the sides of the hatch. (Is this getting confusing?)

Image

Plan A on for that 'drop was to attach the fenders to the walls –-thus the hardpoints. In the end, I deferred to attach them to the chassis. This teardrop was built to boondock and I just don't think wall-mounted fenders are a good idea in the sticks. A damaged fender may mean a damaged wall.

You'll also note a horizontal piece above the fender points. The galley counter protrudes inside the cabin to form the lower shelf and thus it needed hard points on the wall. The stub just above it is for the upper shelf. And that little chunk above it is a hard point for a hook to hang clothes. So anywhere you are going to attach something you'll need a hard point.

"I think 3/4" plywood for the cabinets and skeleton." I built a little 4x8 and used 1/2" ply for the skeleton. Attaching the ceiling on that narrow lip was a challenge but it worked. It's my opinion after that build that it is better to stick with a 3/4" skeleton but skinny it down.

Here's the ledge on that little drop:

Image

"My plan for the skeleton is to leave 3/4" of material around the entire outside and the door area then leave the same where my cabinets are. Is 3/4" enough?" It depends on the location. Assuming you are going to build a ledge to attach your ceiling and spars, I would feel more comfortable with at least 1 & 1/2" to avoid splitting. And again I'd want more meat to attach the wall to the floor. I join my walls to the floor using pocket holes on the side, screws from the bottom, and of course glue.

Image


"...but my understaing is most of us are making the skeleton stronger than needed..."
I'm sure we do. But cutting a skeleton edge from (let's say) 2" down to 3/4" isn't saving much weight. (Think for a moment what that piece would weigh.)

If you want to reduce weight, take a hard look at the steel in your chassis.

:thinking:

Tony :beer:

Epilogue: Take another look at that skeleton of mine. Mentally remove an inch or so of wood around it and then weigh that piece in your mind. :thinking:
Image
User avatar
tony.latham
Gold Donating Member
 
Posts: 2830
Images: 17
Joined: Mon Jul 08, 2013 4:03 pm
Location: Middle of Idaho on the edge of nowhere

Re: Sandwich Skeleton Questions aka Getting Meat Off the Bon

Postby Esteban » Sun Mar 04, 2018 4:46 pm

I favor fiberglassing the exterior skin instead of using aluminum sheets and trim pieces. I've estimated a fiberglass skin weighs 1/10th as much as an aluminum skin, providing considerable weight savings. Fiberglass adds structural strength, which may allow you to build a lighter weight inner framework and/or use thinner/lighter plywood on the inside and outside. Fiberglassing is very cost competitive with aluminum. Fiberglassing provide superior water/weather proofing. Fiberglassing provides more freedom to build a teardrop trailer with what ever dimensions you prefer.

Some suppliers:
https://www.saf.com/aluminum-sheet/
http://www.raka.com/
http://www.uscomposites.com/

I think 1/2" plywood is fine for cabinets. Especially if you use 1/2" Baltic birch where appropriate.
Steve - SLO, CA
Esteban
Donating Member
 
Posts: 1636
Images: 15
Joined: Fri Jul 28, 2006 4:39 pm
Location: California, San Luis Obispo
Top

Re: Sandwich Skeleton Questions aka Getting Meat Off the Bon

Postby eodmike » Sun Mar 04, 2018 5:48 pm

I am just afraid of fiberglassing. I've never done it and don't know anyone who has so there is that.

0.04 aluminum is pretty light and I love the look of the old airstreams.

I'll look at thickening up the skeleton per your suggestion. The cutting for me will be minimal. Where did you find the build taking the longest? I have plans on cutting the skeleton and skins with the water jet and maybe the cabinet area too. Meaning I'll only have to Ikea build it. How long do you figure that takes?
eodmike
Teardrop Inspector
 
Posts: 11
Joined: Tue Feb 27, 2018 5:35 pm
Top

Re: Sandwich Skeleton Questions aka Getting Meat Off the Bon

Postby tony.latham » Sun Mar 04, 2018 6:12 pm

Where did you find the build taking the longest? ... How long do you figure that takes?


It all takes time... and for me ––and I'm a retired old goat, I can see the end of the road after two months. But I plod. And I get distracted and need to fish or take a nap.

Image

Tony
Image
User avatar
tony.latham
Gold Donating Member
 
Posts: 2830
Images: 17
Joined: Mon Jul 08, 2013 4:03 pm
Location: Middle of Idaho on the edge of nowhere
Top

Re: Sandwich Skeleton Questions aka Getting Meat Off the Bon

Postby eodmike » Mon Mar 05, 2018 7:33 am

I've got fingers crossed that I'll be able to do it a bit faster with the cutting being done by waterjet. Who knows. I'll bust my ass and I have the added benefit of all weekends being 3 day weekends so that should help.

I've been reading a lot about weight and with my trailer being built 5x8 if I'm reading right I shouldn't struggle too much keeping it under 1,000. The graph I saw suggest that an average build will be 1,000 at that size and a light weight can be 600. I am also thinking of getting the aluminum trailer instead of the steel. Then if I do a bit of water jetting on the skeleton that should shave a few pounds. Only planning on putting in a 12v system. No big appliances.

I'm going to go ahead and buy the book you suggested. I'll do the spars the way you mentioned so I'll stick with 3/4" plywood for the skeleton. How about the cabinets? 1/2" ok there?
eodmike
Teardrop Inspector
 
Posts: 11
Joined: Tue Feb 27, 2018 5:35 pm
Top

Re: Sandwich Skeleton Questions aka Getting Meat Off the Bon

Postby earl84 » Mon Mar 05, 2018 8:29 am

Are you asking about 3/4” for face frames on your cabinets? I built my cabinets in place, essentially using the teardrop walls as the cabinet walls, then small 1 x 2 cleats all around to support the shelves, and 1/8” ply for the shelves and dividers between cabinets. Pretty light. I used screws to hold them in place while the glue dried, then was going to remove them for weight savings, but didn’t in the end. I wasn’t overly concerned about weight. TB2 is very strong on a wood to wood joint, so you could consider only using glue versus screws. It doesn’t save much weight, but ounces here and there start adding up to pounds.
Another thing to consider is not having interior cabinet doors. I started using my teardrop before it was totally complete, and found that we really liked not having doors on the interior cabinets. It made accessing our bags super easy. Not ever going to have doors in the interior. Do as Tony said and install hardpoints for coat hooks. They are invaluable and worth whatever small weight penalty you might pay.
User avatar
earl84
Donating Member
 
Posts: 36
Images: 23
Joined: Sun Jan 31, 2016 2:15 pm
Location: Denver, CO
Top

Re: Sandwich Skeleton Questions aka Getting Meat Off the Bon

Postby eodmike » Mon Mar 05, 2018 8:58 am

In the generic benroy plan on this site it uses 3/4 ply for everything in the galley. The shelfs, faceboards, doors, ect. The outside walls are used so by default those are 3/4" since that's what my wall is but does the faceboard, shelf, and doors need to be that. I know the doors don't. I would assume the face board wouldn't. I would guess the shelf would be nice if 3/4". The drawers and the dividers that help support the weight of the shelfs??? The bulkhead itself???

Here is a link to the plans it might clear things up a bit. http://www.mikenchell.com/images/GenericBenroyPlans.pdf
eodmike
Teardrop Inspector
 
Posts: 11
Joined: Tue Feb 27, 2018 5:35 pm
Top

Re: Sandwich Skeleton Questions aka Getting Meat Off the Bon

Postby earl84 » Tue Mar 06, 2018 8:55 am

I think the main thing about construction of a teardrop, especially skeletonized walls, is to think airplane, not tank. If you’ve ever seen how thin the stringers are on an actual wing and how light and strong it is, you’ll be convinced. The combination of parts fitting together and being glued creates an amazingly strong structure. The key is to have solid wood anywhere that you will be screwing a shelf, a countertop cleat, a coat hook, whatever, into so that you aren’t asking 1/8” plywood to hold weight.
Want a demonstration that exists in every house? Go look at your kitchen cupboards. How much weight is that super thin sheet of plywood on the lower shelves holding. The structure, and strength, and stiffness is from the smart construction, not the thin wood holding 50 pounds of stoneware plates. Convince yourself. Build a small scale skeletonized wall with nothing but 1/8” plywood skins on both sides, 1x2 skeleton, and TB2 only holding it together. Let it cure, then try to take it apart or bend it. Good luck. Now imagine that test piece glued to other equally strong pieces, and it just keeps getting stronger and stronger.
I think the plans call for 3/4” everywhere is because it makes sourcing wood super easy, it makes construction easier, it’s undoubtedly strong, but probably way overkill.
User avatar
earl84
Donating Member
 
Posts: 36
Images: 23
Joined: Sun Jan 31, 2016 2:15 pm
Location: Denver, CO
Top

Re: Sandwich Skeleton Questions aka Getting Meat Off the Bon

Postby tony.latham » Tue Mar 06, 2018 11:35 am

But here's the deal... you HAVE to video the waterjet cutter cutting your skeleton and share it with us.

It's forum rule #37b3. ;)

Tony
Image
User avatar
tony.latham
Gold Donating Member
 
Posts: 2830
Images: 17
Joined: Mon Jul 08, 2013 4:03 pm
Location: Middle of Idaho on the edge of nowhere
Top

Re: Sandwich Skeleton Questions aka Getting Meat Off the Bon

Postby eodmike » Tue Mar 06, 2018 2:31 pm

No problem. I can't do it to the end of April or beginning of May. You see the water jet is a little fussy with the glue that is in plywood. So the issue we'll have is it'll cause the water to foam. The good news is at that time period we have a routine pump out of the water. So I'm going to jump in just before that and cut my plywood and skins. The skins shouldn't matter and could be done at anytime since they are aluminum.

I'm really hoping if I design enough of it that this will go together super quick since I can't start assembly with the walls until beginning of May worse case.

I'm thinking with my models and what not that I can order the trailer soon (looking at aluminum NothernTool 5x8 https://www.northerntool.com/shop/tools/product_200660344_200660344). However I'm not sure if the 90lb difference is worth the $200 difference? Then I'll build the floor (all straight cuts don't see the point of water jetting that). I'm wondering if I can actually build my lower bulkhead up to the counter top and get that taken care of? Thoughts. I mean I can do my counter top or upper bulkhead because I'll need the walls to support that. But I guess I don't see reason I cant do the lower stuff. I'm also considering doing a head board so I could probably do that as well? So when I get my walls I can throw them on and be a good way done?
eodmike
Teardrop Inspector
 
Posts: 11
Joined: Tue Feb 27, 2018 5:35 pm
Top

Re: Sandwich Skeleton Questions aka Getting Meat Off the Bon

Postby mikeschn » Tue Mar 06, 2018 5:24 pm

I've tried the plywood route a number of times... it was never light enough... Until I finally did the MadDash! This is something you can tow with your Nissan. And it looks like aluminum!!!

Image

Here's the build thread...

viewtopic.php?p=1110105#p1110105

Oh yea, don't forget some nice wheels!

Image

Mike...
The quality is remembered long after the price is forgotten, so build your teardrop with the best materials...
User avatar
mikeschn
Site Admin
 
Posts: 19185
Images: 479
Joined: Tue Apr 13, 2004 11:01 am
Location: MI
Top

Re: Sandwich Skeleton Questions aka Getting Meat Off the Bon

Postby friz » Tue Mar 06, 2018 7:24 pm

If you can get curves in most of the surfaces, the shell gets real stiff with minimal thickness. This is the CLC kit. Queen size bed, 500 lbs empty. My car doesn't have a tow rating.Image

Sent from my SM-G930V using Tapatalk
The "Sin Bin"
150133
User avatar
friz
The 300 Club
 
Posts: 417
Images: 2
Joined: Mon Jan 03, 2011 10:01 pm
Top

Re: Sandwich Skeleton Questions aka Getting Meat Off the Bon

Postby eodmike » Wed Mar 07, 2018 2:21 am

Friz I just read through your build this weekend. I looked long and hard at the kit. I really like it. With that said the fiberglass freaks me out. I think I'm worried it would be tedious for me and I'd lose interest in it. It looks soo hard. LOL. But lovely craft and so light.

Mike I hadn't seen your build thread. I just finished it. Impressive. I had looked at foamies but hadn't seen any with a galley. Now that I've seen yours maybe it is worth doing. I know the waterjet cuts foam like butter and no foaming issues so I could start with foam sooner. The plywood pieces I could cut later and fit. I would really like to find a way to sandwich the foam in a hard skin inside and out. Any builds that do that? I know the foam is strong enough. I'm just stubborn I guess.
eodmike
Teardrop Inspector
 
Posts: 11
Joined: Tue Feb 27, 2018 5:35 pm
Top

Re: Sandwich Skeleton Questions aka Getting Meat Off the Bon

Postby tony.latham » Wed Mar 07, 2018 10:24 am

With that said the fiberglass freaks me out.


It shouldn't. I've been using fiberglass off and on for forty years. Watch some Youtube videos on it. It's no big deal.

Here's a primer:



Just mix your epoxy in small doses –- a big pot gives off heat and causes it to "go off."

Tony
Image
User avatar
tony.latham
Gold Donating Member
 
Posts: 2830
Images: 17
Joined: Mon Jul 08, 2013 4:03 pm
Location: Middle of Idaho on the edge of nowhere
Top

Next

Return to Teardrop Construction Tips & Techniques

Who is online

Users browsing this forum: No registered users and 1 guest