Need Fiberglass Foam Core Panel Recommendation
- Thread starter bapple
- Start date
Angles glued to edges/corners is the common joining and reinforcing method, but if you look at the Styromax videos linked earlier, they don't even do that. They just glue the edges...
Was the Defender camper all hand layup or just the edges?
I’ve actually messaged Styromax and I’m fairly certain they actually bond aluminum edging on their panel build up’s. If you look through their website you will see all the extrusions that they sell and their build methods.
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turbothrush
Member
About 10 years ago, in response to questions from a friend, I put together a Powerpoint to answer some sandwich panel construction methods that I used, but this site won't let me attach it
It includes making doors which was something that I did not want to do at all. Clearly not the only way, but the way I used.
I guess I could post the dozen pics involved if anyone wants to see them.
Cheers,
Peter OKA196 motorhome
I for one would love to see the dozen or so pics you mention. Very little on the web about this type of construction that I could find
Peter_n_Margaret
Adventurer
The flat panels wer made individually on his shed floor, laid up wet on wet and vacuum bagged, all by hand.
NOTE some lesser quality panels are made by gluing pre made skins to the foam. BEST quality is made wet on wet in a single operation that gives better adhesion and lighter skins.
This also allowed him to custom make each panel specifically for the application - vis - thicker or thinner foam and thicker or thinner skins.
The corners were all made by hand - glue in a block of foam, carve it to shape inside and out and then lay up the glass inside and out, again, all by hand.
Note that the finish on the glass is two pack paint, not gel coat. I think gel coat is superior. Mine is high quality, high gloss white gel coat one side and 2 pack paint on the other (rough) side.
Cheers,
Peter
OKA196 motorhome
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rruff
Explorer
The great majority use the glued on skins. I'm doing wet layup epoxy over XPS, but no vacuum bagging. My reasoning was that I wanted an aero nose above the cab, plus rounded corners, and the glued on skins make this difficult. Also, joining and sealing all the edges is easy with wet FG. I'm going to gelcoat the exterior also.
It's hard to get perfectly flat surface though, when you have overlapping rolls of FG cloth! I decided not to worry about it...
This is all quite timely, I'm about to pull the trigger on some Carbon Core honeycomb panels for a small hard-sided pop-up camper built on top of an M101A military trailer to pull behind my HDJ81 Landcruiser. This is my first post here, great community, tons of quality info about these camper shell builds!
I never thought of FRP profiles vs. aluminum profiles for attaching the edges prior to coming across this thread but it's genius. I was worried about thermal expansion differences between the AL and fiberglass. Peter's comments about the size of his glue joints confirmed my concerns. So, I'm going with FRP profiles instead. And they're much cheaper!
For those who might find this later, I've found a few suppliers of FPR profiles (there are many others, Grainger for example):
https://www.eplastics.com/fiberglass/profiles
https://bedfordreinforced.com/products/proforms-structural-shapes/
That said, it seems like most folks are going with 3x3 angle on the exterior so I suppose that's what I'll use. If I use FPR profiles then would I still want to use Sika for the glue or would I just epoxy it all together since the whole structure should behave the same?
I never thought of FRP profiles vs. aluminum profiles for attaching the edges prior to coming across this thread but it's genius. I was worried about thermal expansion differences between the AL and fiberglass. Peter's comments about the size of his glue joints confirmed my concerns. So, I'm going with FRP profiles instead. And they're much cheaper!
For those who might find this later, I've found a few suppliers of FPR profiles (there are many others, Grainger for example):
https://www.eplastics.com/fiberglass/profiles
https://bedfordreinforced.com/products/proforms-structural-shapes/
That said, it seems like most folks are going with 3x3 angle on the exterior so I suppose that's what I'll use. If I use FPR profiles then would I still want to use Sika for the glue or would I just epoxy it all together since the whole structure should behave the same?
The Artisan
Adventurer
I used 14 guage broke steel on my prototype. Next build I will be using 16 guage.
Kevin
https://www.expeditionportal.com/forum/threads/fuso-composite-camper-under-construction.163571/
Kevin
https://www.expeditionportal.com/forum/threads/fuso-composite-camper-under-construction.163571/
Well, hell, not sure why I didn't think of that. I've got some 16g structural members from an old steel building sitting on my property and, while they are not nearly as strong as 3x3x1/8" AL, they are probably more than adequate especially considering that there will be reinforcement on the inside as well. I think I'll give this a shot, the price is certainly right! Thanks for the tip!
Steel has perhaps a quarter the thermal expansion of fiberglass, so definitely need Sika for the joints.
Edit to add comparative weights of identical lengths (specific to one half of my popup build) of various materials, all 3x3 angles at thicknesses specified below:
AL 3/16: 16.66lbs
FRP 1/4: 15.08lbs
Steel 16g: 16.52lbs
Steel 14g: 20.27lbs
As you can see, they're all very similar. Switching from 3/16 AL to 14g steel would add ~8lbs overall to my build but save me thousands of dollars. Not as bomb-proof but for the cost savings I could nearly rebuild the damn thing if it breaks so it's worth the risk IMO.
Steel has perhaps a quarter the thermal expansion of fiberglass, so definitely need Sika for the joints.
Edit to add comparative weights of identical lengths (specific to one half of my popup build) of various materials, all 3x3 angles at thicknesses specified below:
AL 3/16: 16.66lbs
FRP 1/4: 15.08lbs
Steel 16g: 16.52lbs
Steel 14g: 20.27lbs
As you can see, they're all very similar. Switching from 3/16 AL to 14g steel would add ~8lbs overall to my build but save me thousands of dollars. Not as bomb-proof but for the cost savings I could nearly rebuild the damn thing if it breaks so it's worth the risk IMO.
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The Artisan
Adventurer
I was going to use alum but as you have shown strength to weight ratio, is about the same. I am using 16 guage on my clients 18 footer. From my buddies calc in strength and weight is 1/4" alum is same as 16 guage steel.
Kevin
Kevin
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Well, not exactly. I've shown that the WEIGHTS are the same but I didn't speak to strength.
Geek out moment:
A simple bending analysis of 3x3 16g angle steel vs. 1/4" AL over a 6' span with a 100lb load centered shows that the aluminum has 3,450psi of bending stress while the steel has 13,145psi of bending stress. This is 10% the yield strength of AL while it's 33% the yield strength of A36 steel. Using a typical Factory of Safety of 3 (i.e., we want our material to be 3X stronger than our worst-case loading condition) this is as much as you'd ever want to load a 16g 3x3 angle profile. That said, given an identical profile size, 16g steel isn't remotely close to 1/4" AL--basically the AL could take 3X more weight (300lbs) before you hit a Factory of Safety of 3 on its yield strength.
Sometimes we care about deflection too. At this load, the 16g also has 33% more deflection than the AL (0.08" vs. 0.06"). The deflection is inversely related to the modulus of elasticity for the material. Since the modulus of elasticity of steel is 3X that of AL, you can use 1/3rd the thickness of steel and get the same deflection as AL. In this case 0.083" steel gives the same deflection as 0.25" AL.
The deflection is also inversely related to the moment of inertia of the profile's cross-section, I. So deflection depends upon the profile shape AND the material's properties. The stress is only dependent on I (shape) and not at all on the modulus of elasticity (material properties). Even at 0.083" thickness the steel still sees significantly higher stress than 0.25" AL because the difference in thickness makes the profile property I much larger in the AL.
Anyway, this doesn't really matter because who said 1/4" AL was necessary to begin with? The real strength of the structure comes from the panels, not the metal. All the metal is really doing is holding the panels together. I'm going with 16g based upon your recommendation and I'm planning on welding the perimeter together for S&Gs so it should be strong as hell!
Geek out moment:
A simple bending analysis of 3x3 16g angle steel vs. 1/4" AL over a 6' span with a 100lb load centered shows that the aluminum has 3,450psi of bending stress while the steel has 13,145psi of bending stress. This is 10% the yield strength of AL while it's 33% the yield strength of A36 steel. Using a typical Factory of Safety of 3 (i.e., we want our material to be 3X stronger than our worst-case loading condition) this is as much as you'd ever want to load a 16g 3x3 angle profile. That said, given an identical profile size, 16g steel isn't remotely close to 1/4" AL--basically the AL could take 3X more weight (300lbs) before you hit a Factory of Safety of 3 on its yield strength.
Sometimes we care about deflection too. At this load, the 16g also has 33% more deflection than the AL (0.08" vs. 0.06"). The deflection is inversely related to the modulus of elasticity for the material. Since the modulus of elasticity of steel is 3X that of AL, you can use 1/3rd the thickness of steel and get the same deflection as AL. In this case 0.083" steel gives the same deflection as 0.25" AL.
The deflection is also inversely related to the moment of inertia of the profile's cross-section, I. So deflection depends upon the profile shape AND the material's properties. The stress is only dependent on I (shape) and not at all on the modulus of elasticity (material properties). Even at 0.083" thickness the steel still sees significantly higher stress than 0.25" AL because the difference in thickness makes the profile property I much larger in the AL.
Anyway, this doesn't really matter because who said 1/4" AL was necessary to begin with? The real strength of the structure comes from the panels, not the metal. All the metal is really doing is holding the panels together. I'm going with 16g based upon your recommendation and I'm planning on welding the perimeter together for S&Gs so it should be strong as hell!
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The Artisan
Adventurer
sorry 3/16. You have to keep in mind this is just reinforcing and protecting your edges. The strength in the box is in the panels.
Kevin
Kevin
rruff
Explorer
Practically speaking you'd want the material you bond on the edges and corners to be a bit stronger than the skins, but not too much. 2x would be plenty.
Another consideration is protection from tree branches. They can exert a lot of force on a sharp edge.
Peter_n_Margaret
Adventurer
The aluminium angles I used on the corners of the OKA body are all 1.6mm, except where they might get scrub impact and they are 3mm. The highest impact zone (the 45 degree bits on the outer front edges of the bed-over-cab) are 3mm steel.
Cheers,
Peter
OKA196 motorhome
Cheers,
Peter
OKA196 motorhome