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PostPosted: March 9, 2018, 8:52 am 
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I have a project coming up that will require kind of a rounded boat tail rear body section.

My thought were to make something from foam and then glass over, but with all of the research I've done, there really is not a clear method of going this.

I was wondering if anyone here has fabricated body panels with a foam core?

In most of the cases I've seen they do the shell and then dissolve the foam leaving just the shell.

I can see having a mold and laying it inside to get a smooth surface, but when overlaying foam, getting a smooth outer surface has some challenges.

Any tips, suggests, or leads to some "how to" videos would be greatly appreciated.

Thanks and have a great day.

Dan

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PostPosted: March 9, 2018, 9:46 am 
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Dan, the reason that you have not found a clear method is that there is no one way. There are many ways to accomplish your goal. Making a mold 1st is just a lot of extra work for a one-off project IMO. I am definitely in the buck vs mold camp.

There are many different materials and prcesses to make the fiberglass parts. I created a way to use inexpensive polystyrene foam and polyester resin using common household materials. These are normally thought of as being incompatible materials. I used that process to make my half-doors (never finished the doors though). You can fide that discussion here: viewtopic.php?f=35&t=4145&start=553 and the next few pages.

Whether you decide to use a buck or a mold process, there will be sanding and filling, and sanding and filling and sanding......

We are an eclectic bunch here and each of us have our own skills and preferences. Do some searching here and you will find other methods.

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PostPosted: March 9, 2018, 10:06 am 
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Check out Zac88GT's thread. It has some great stuff in there. viewtopic.php?f=36&t=12106&start=90

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PostPosted: March 9, 2018, 11:15 am 
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Thanks guys for the links.

I was thinking of forming an inner pattern and then laying the glass over for a finished outside finish. Then either snap it loose or hack out the majority of the foam then acetone the rest away. I had thought that I might use like 1/4" plywood to make some of the major form. If careful, I could cut down the plywood later and leave reinforcement ribs. Or as shown in the link, maybe lay in some foam and laminate it to the inside for added strength.

Here's about what I'm looking to make for the trunk area, or boot in the UK...

Image

It will be an undertaking I'm sure. But it will be fun.

Thanks again to booth of you for the links.

Have a great day.

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PostPosted: March 9, 2018, 11:36 am 
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Take some lessons from the cedar strip canoe folks. You can build anything with wood strips and fiberglass.

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PostPosted: March 9, 2018, 12:37 pm 
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A good write-up is here: http://locostusa.com/forums/viewtopic.php?f=23&t=8113

And you can get a few pointers from https://www.rqriley.com/frp-foam.htm

The basic element is that you have to fiberglass BOTH sides of the foam to give it any strength. Be sure to use epoxy resin, not the poly stuff. (Unless you want to melt your work-of-art sculptured bodywork into a big glob of gooey ice cream...) You knew all that already, right?
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The front and rear bodywork on my car is all foam/fiberglass composite work. I'm no expert, but I'll be glad to answer questions if I can.

:cheers:
JDK

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PostPosted: March 9, 2018, 12:49 pm 
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I knew as soon as I posted that I would remember another link... A series of videos on moldless composite stuff:
https://www.youtube.com/watch?v=JJax6pqlEoI

And, since I like showing off, another picture. The rear deck is foam/fiberglass as are the rear fenders.


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PostPosted: March 9, 2018, 5:27 pm 
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Here are links (this site) to some pictures of my fenders and hood under construction. I used foam finished with drywall putty for the front of the nose and a cardboard planked skeleton for the fenders.

viewtopic.php?f=23&t=2292&hilit=nose+hood

viewtopic.php?f=23&t=17716&hilit=foam&start=15

Getting a smooth surface using a male buck as the form means a lot of grinding and sanding. I used a belt sander with a coarse grit to get most of the pattern off, smoothed that a bit with hand sanding and then used layers of high build primer. It was my first experience with painting so there are some imperfections, but I was quite happy with the result.

John


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PostPosted: March 9, 2018, 6:50 pm 
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Thanks again everyone.

I'll take some time this weekend and go over the links and videos.

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PostPosted: March 9, 2018, 11:33 pm 
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Thanks and have a great day.

Dan[/quote]

As my build involves a compound curve roof and nose I had to face the problem you are describing. I chose to read about dinghy hull building and learned what I needed. My approach was balsa wood panels (they are light and scored) over a frame also called plug. The balsa follows any curve and what you have to do is brush two part resin, sand it until you get the shape you want and then start layering glass fiber. A lot of sanding is involved. I have talked about this on another thread:

viewtopic.php?f=18&t=18940


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PostPosted: March 9, 2018, 11:43 pm 
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http://locostusa.com/forums/viewtopic.p ... ilit=resin

That's my sole foray into the world of fibreglass over foam. It worked well, and could have worked even better if I already had some experience. One thing to keep in mind is that your foam needs to be smaller than the finished part by the exact thickness of the fiberglass: Might be tough to gauge that on a complex panel.

Cheers.

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PostPosted: March 18, 2018, 12:41 pm 
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C10CoryM wrote:
One thing to keep in mind is that your foam needs to be smaller than the finished part by the exact thickness of the fiberglass: Might be tough to gauge that on a complex panel.


If you're willing to spend the time, its a good reason to use the foam as a buck to make a mold then pull the part from the mold. The mold will also leave a nicer outer surface so the finished part will ultimately be lighter without all of the filler.

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PostPosted: March 18, 2018, 1:41 pm 
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a.moore wrote:
C10CoryM wrote:
One thing to keep in mind is that your foam needs to be smaller than the finished part by the exact thickness of the fiberglass: Might be tough to gauge that on a complex panel.


If you're willing to spend the time, its a good reason to use the foam as a buck to make a mold then pull the part from the mold. The mold will also leave a nicer outer surface so the finished part will ultimately be lighter without all of the filler.


You nailed it. Including the "If you're willing to spend the time" part; which I wasn't :mrgreen: That being said, the finish really wasn't that bad on a simple part like a scuttle.

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